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Christophe Ampe - One of the best experts on this subject based on the ideXlab platform.
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On the origin and evolution of vertebrate and viral Profilins.
FEBS letters, 2006Co-Authors: Debby Polet, Anja Lambrechts, Klaas Vandepoele, Joël Vandekerckhove, Christophe AmpeAbstract:The three dimensional structures of Profilins from invertebrates and vertebrates are remarkably similar despite low sequence similarity. Their evolutionary relationship remains thus enigmatic. A phylogenetic analysis of Profilins from Deuterostoma indicates that Profilin III and IV isoforms each form distinct groups. Profilin IV is most related to invertebrate Profilins and originated prior to vertebrate evolution whereas separation of Profilin I, II and III isoforms occurred early in vertebrate evolution. Viral Profilins are most similar to Profilin III. In silico analysis of representative Profilin gene structures corroborates the phylogenetic result and we discuss this in terms of biochemical differences.
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a role for complexes of survival of motor neurons smn protein with gemins and Profilin in neurite like cytoplasmic extensions of cultured nerve cells
Experimental Cell Research, 2005Co-Authors: Aarti Sharma, Anja Lambrechts, Christophe Ampe, Le Thi Hao, Caroline Sewry, Arthur H M Burghes, Glenn E MorrisAbstract:Abstract Spinal muscular atrophy (SMA) is caused by reduced levels of SMN (survival of motor neurons protein) and consequent loss of motor neurons. SMN is involved in snRNP transport and nuclear RNA splicing, but axonal transport of SMN has also been shown to occur in motor neurons. SMN also binds to the small actin-binding protein, Profilin. We now show that SMN and Profilin II co-localise in the cytoplasm of differentiating rat PC12 cells and in neurite-like extensions, especially at their growth cones. Many components of known SMN complexes were also found in these extensions, including gemin2 (SIP-1), gemin6, gemin7 and unrip (unr-interacting protein). Coilin p80 and Sm core protein immunoreactivity, however, were seen only in the nucleus. SMN is known to associate with β-actin mRNA and specific hnRNPs in axons and in neurite extensions of cultured nerve cells, and SMN also stimulates neurite outgrowth in cultures. Our results are therefore consistent with SMN complexes, rather than SMN alone, being involved in the transport of actin mRNPs along the axon as in the transport of snRNPs into the nucleus by similar SMN complexes. Antisense knockdown of Profilin I and II isoforms inhibited neurite outgrowth of PC12 cells and caused accumulation of SMN and its associated proteins in cytoplasmic aggregates. BIAcore studies demonstrated a high affinity interaction of SMN with Profilin IIa, the isoform present in developing neurons. Pathogenic missense mutations in SMN, or deletion of exons 5 and 7, prevented this interaction. The interaction is functional in that SMN can modulate actin polymerisation in vitro by reducing the inhibitory effect of Profilin IIa. This suggests that reduced SMN in SMA might cause axonal pathfinding defects by disturbing the normal regulation of microfilament growth by Profilins.
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Profilin II is alternatively spliced, resulting in Profilin isoforms that are differentially expressed and have distinct biochemical properties.
Molecular and cellular biology, 2000Co-Authors: Anja Lambrechts, Attila Braun, Attila Aszódi, Joël Vandekerckhove, Veronique Jonckheere, Lorene M. Lanier, Johan Robbens, Inge Van Colen, Reinhard Fässler, Christophe AmpeAbstract:We deduced the structure of the mouse Profilin II gene. It contains five exons that can generate four different transcripts by alternative splicing. Two transcripts encode different Profilin II isoforms (designated IIa and IIb) that have similar affinities for actin but different affinities for polyphosphoinositides and proline-rich sequences. Profilins IIa and IIb are also present in humans, suggesting that all mammals have three Profilin isoforms. Profilin I is the major form in all tissues, except in the brain, where Profilin IIa is most abundant. Profilin IIb appears to be a minor form, and its expression is restricted to a limited number of tissues, indicating that the alternative splicing is tightly regulated. Western blotting and whole-mount in situ hybridization show that, in contrast to the expression of Profilin I, the expression level of Profilin IIa is developmentally regulated. In situ hybridization of adult brain sections reveals overlapping expression patterns of Profilins I and IIa.
Rudolf Valenta - One of the best experts on this subject based on the ideXlab platform.
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Oligomerization of Profilins from birch, man and yeast. Profilin, a ligand for itself?
Sexual Plant Reproduction, 1998Co-Authors: Irene Mittermann, Jacquelyn S. Fetrow, Diana L. Schaak, Steven C. Almo, Dietrich Kraft, Erwin Heberle-bors, Rudolf ValentaAbstract:Profilins are structurally well conserved low molecular weight (12–15 kDa) eukaryotic proteins which interact with a variety of physiological ligands: (1) cytoskeletal components, e.g., actin; (2) polyphosphoinositides, e.g., phosphatidylinositol-4,5-bisphosphate; (3) proline-rich proteins, e.g., formin homology proteins and vasodilatator-stimulated phosphoprotein. Profilins may thus link the microfilament system with signal transduction pathways. Plant Profilins have recently been shown to be highly crossreactive allergens which bind to IgE antibodies of allergic patients and thus cause symptoms of type I allergy. We expressed and purified from Escherichia coli Profilins from birch pollen (Betula verrucosa), humans (Homo sapiens) and yeast (Schizosaccharomyces pombe) and demonstrated that each of these Profilins is able to form stable homo- and heteropolymers via disulphide bonds in vitro. Circular dichroism analysis of oxidized (polymeric) and reduced (monomeric) birch pollen Profilin indicates that the two states have similar secondary structures. Using 125I-labeled birch pollen, yeast and human Profilin in overlay experiments, we showed that disulphide bond formation between Profilins can be disrupted under reducing conditions, while reduced as well as oxidized Profilin states bind to actin and Profilin-specific antibodies. Exposure of Profilin to oxidizing conditions, such as when pollen Profilins are liberated on the surface of the mucosa of atopic patients, may lead to Profilin polymerization and thus contribute to the sensitization capacity of Profilin as an allergen.
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the molecular basis for allergen cross reactivity crystal structure and ige epitope mapping of birch pollen Profilin
Structure, 1997Co-Authors: Alexander Fedorov, Rudolf Valenta, Tanja Ball, Nicole M Mahoney, S C AlmoAbstract:Abstract Background: The Profilins are a group of ubiquitous actin monomer binding proteins that are responsible for regulating the normal distribution of filamentous actin networks in eukaryotic cells. Profilins also bind polyphosphoinositides, which can disrupt the Profilin–action complex, and proline-rich ligands which localize Profilin to sites requiring extensive actin filament accumulation. Profilins represent cross-reactive allergens for almost 20 % of all pollen allergic patients. Results: We report the X-ray crystal structure of birch pollen Profilin (BPP) at 2.4 A resolution. The major IgE-reactive epitopes have been mapped and were found to cluster on the N- and C-terminal α helices and a segment of the protein containing two strands of the β sheet. The overall fold of this protein is similar to that of the mammalian and amoeba Profilins, however, there is a significant change in the orientation of the N-terminal α helix in BPP. This change in orientation alters the topography of a hydrophobic patch on the surface of the molecule, which is thought to be involved in the binding of proline-rich ligands. Conclusions: Profilin has been identified as an important cross-reactive allergen for patients suffering from multivalent type I allergy. The prevalent epitopic areas are located in regions with conserved sequence and secondary structure and overlap the binding sites for natural Profilin ligands, indicating that the native ligand-free Profilin acts as the original cross-sensitizing agent. Structural homology indicates that the basic features of the G actin–Profilin interaction are conserved in all eukaryotic organisms, but suggests that mechanistic differences in the binding of proline-rich ligands may exist. The structure of BPP provides a molecular basis for understanding allergen cross-reactivity.
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Molecular cloning and characterization of Profilin from tobacco (Nicotiana tabacum): increased Profilin expression during pollen maturation.
Plant molecular biology, 1995Co-Authors: Irene Mittermann, Rudolf Valenta, Dietrich Kraft, Ines Swoboda, Elisabeth S. Pierson, Norbert Eller, Erwin Heberle-borsAbstract:Profilin has recently been identified as an actin-binding protein in higher plants. A cDNA coding for tobacco Profilin, which shared an average sequence identity of 75% with other plant Profilins, was isolated from a tobacco pollen cDNA library by antibody screening. Tobacco Profilin was expressed in Escherichia coli and purified by affinity to poly-(L-proline) Sepharose. A rabbit antiserum was raised against recombinant tobacco Profilin and used to estimate the amount of Profilin expressed in different tobacco tissues. Profilin can be detected in different somatic tissues, but the expression is 50–100 fold higher in mature pollen. Immunofluorescence and confocal laser scanning microscopy showed a homogeneous distribution of Profilin in the cytoplasm of in vitro cultured pollen grains and pollen tubes of tobacco whereas some growing pollen tubes were stained more intensively a their tip. A possible role of pollen Profilin as a developmentally upregulated microfilament precursor in mature pollen is discussed.
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INTERACTION OF PLANT Profilin WITH MAMMALIAN ACTIN
European journal of biochemistry, 1994Co-Authors: Klaudia Giehl, Martin Rothkegel, Rudolf Valenta, Melanie Ronsiek, Hans-georg Mannherz, Brigitte M. JockuschAbstract:The mode of interaction of birch and bovine Profilins with actin was compared using a number of techniques. Birch Profilin was purified from pollen or as a recombinant protein from Escherichia coli, using poly(l-proline) affinity chromatography and a monoclonal antibody for the identification of the isolated product. On two-dimensional gels, the genuine and recombinant proteins were identical in molecular mass and isoelectric point and revealed that birch Profilin, in contrast to the basic Profilins found in mammals, is an acidic protein, analogous to maize Profilins. Bovine Profilin was obtained from calf thymus. In viscometric assays, the birch protein was seen to modulate actin filament formation analogous to animal Profilin. Birch Profilin increased the critical concentration required for muscle and brain actin polymerization in a concentration-dependent manner, supporting the notion of the formation of a heterologous complex between the plant protein and animal actin. The effect was Mg2+-sensitive, as had been described for homologous complexes. The dissociation constants obtained for the plant/vertebrate and the vertebrate/vertebrate system were both in the micromolar range. The affinity of birch Profilin for muscle actin was slightly lower than that for nonmuscle (brain) actin. A binary complex of birch Profilin and skeletal muscle actin could be isolated by gel chromatography. Cross-linking experiments with actin, birch Profilin, the G-actin binding peptide thymosin β4 and gelsolin segment 1, the N-terminal fragment of an actin capping protein, showed that Profilin competed with thymosin β4, but had no effect on segment 1 binding to actin. These data indicate that the actin-binding domains in plant and animal Profilins are functionally highly conserved, although the overall sequence similarity is less than 25%.
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cDNA cloning and expression of timothy grass (Phleum pratense) pollen Profilin in Escherichia coli : comparison with birch pollen Profilin
Biochemical and biophysical research communications, 1994Co-Authors: Rudolf Valenta, Tanja Ball, Susanne Vrtala, Michael Duchêne, D. Kraft, Otto ScheinerAbstract:Abstract Profilin, an actin-binding protein,was previously described as a ubiquitous allergen which is responsible for cross-reactivities in about 20% of pollen and food allergic patients. A complete cDNA clone coding for timothy grass ( Phleum pratense ) pollen Profilin was isolated using allergic patients IgE. The deduced amino acid sequence of timothy grass Profilin shares a sequence identity of 79% with birch Profilin and other plant Profilins and a lower average sequence identity of 35% with other eukaryotic Profilins. The high degree of homology among different plant Profilins at the DNA and protein level explains the extensive cross-reactivities observed in Profilin allergic patients. Recombinant timothy grass pollen Profilin was expressed in Escherichia coli as a β-galactosidase fusion protein and shown to bind IgE from Profilin allergic patients similar to recombinant birch Profilin. Slight differences regarding the IgE-binding capacity of birch and timothy grass Profilin indicate that not all IgE-epitopes of the two Profilins are conserved. It is speculated that Profilin allergic patients were initially sensitized against a certain Profilin and then cross-react with the homologous proteins.
Walter Witke - One of the best experts on this subject based on the ideXlab platform.
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role of the actin binding protein Profilin1 in radial migration and glial cell adhesion of granule neurons in the cerebellum
Cell Adhesion & Migration, 2012Co-Authors: Marco B Rust, Jan A Kullmann, Walter WitkeAbstract:Profilins are small G-actin-binding proteins essential for cytoskeletal dynamics. Of the four mammalian Profilin isoforms, Profilin1 shows a broad expression pattern, Profilin2 is abundant in the brain, and Profilin3 and Profilin4 are restricted to the testis. In vitro studies on cancer and epithelial cell lines suggested a role for Profilins in cell migration and cell-cell adhesion. Genetic studies in mice revealed the importance of Profilin1 in neuronal migration, while Profilin2 has apparently acquired a specific function in synaptic physiology. We recently reported a mouse mutant line lacking Profilin1 in the brain; animals display morphological defects that are typical for impaired neuronal migration. We found that during cerebellar development, Profilin1 is specifically required for radial migration and glial cell adhesion of granule neurons. Profilin1 mutants showed cerebellar hypoplasia and aberrant organization of cerebellar cortex layers, with ectopically arranged granule neurons. In this commentary, we briefly introduce the Profilin family and summarize the current knowledge on Profilin activity in cell migration and adhesion. Employing cerebellar granule cells as a model, we shed some light on the mechanisms by which Profilin1 may control radial migration and glial cell adhesion. Finally, a potential implication of Profilin1 in human developmental neuropathies is discussed.
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high resolution structural analysis of mammalian Profilin 2a complex formation with two physiological ligands the formin homology 1 domain of mdia1 and the proline rich domain of vasp
Journal of Molecular Biology, 2008Co-Authors: Petri Kursula, Walter Witke, Inari Kursula, Marzia Massimi, Younghwa Song, Joshua Downer, Will A Stanley, Matthias WilmannsAbstract:Abstract Profilins are small proteins capable of binding actin, poly- l -proline and other proline-rich sequences, and phosphatidylinositol (4,5)-bisphosphate. A number of proline-rich ligands for Profilin have been characterised, including proteins of the Ena/VASP and formin families. We have determined the high-resolution crystal structures of mouse Profilin 2a in complex with peptides from two functionally important ligands from different families, VASP and mDia1. The structures show that the binding mode of the peptide ligand is strongly affected by the non-proline residues in the sequence, and the peptides from VASP and mDia1 bind to Profilin 2a in distinct modes. The high resolution of the crystallographic data allowed us to detect conserved CH-π hydrogen bonds between the peptide and Profilin in both complexes. Furthermore, both peptides, which are shown to have micromolar affinity, induced the dimerisation of Profilin, potentially leading to functionally different ligand-Profilin–actin complexes. The peptides did not significantly affect actin polymerisation kinetics in the presence or in the absence of Profilin 2a. Mutant Profilins were tested for binding to poly- l -proline and the VASP and mDia1 peptides, and the F139A mutant bound proline-rich ligands with near-native affinity. Peptide blotting using a series of designed peptides with Profilins 1 and 2a indicates differences between the two Profilins towards proline-rich peptides from mDia1 and VASP. Our data provide structural insights into the mechanisms of mDia1 and VASP regulated actin polymerisation.
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mouse Profilin 2 regulates endocytosis and competes with sh3 ligand binding to dynamin 1
Journal of Biological Chemistry, 2006Co-Authors: Ralph Gareus, Alessia Di Nardo, Vladimir Rybin, Walter WitkeAbstract:Mammalian Profilins are abundantly expressed actin monomer-binding proteins, highly conserved with respect to their affinities for G-actin, poly-L-proline, and phosphoinositides. Profilins associate with a large number of proline-rich proteins; the physiological significance and regulation of which is poorly understood. Here we show that Profilin 2 associates with dynamin 1 via the C-terminal proline-rich domain of dynamin and thereby competes with the binding of SH3 ligands such as endophilin, amphiphysin, and Grb2, thus interfering with the assembly of the endocytic machinery. We also present a novel role for the brain-specific mouse Profilin 2 as a regulator of membrane trafficking. Overexpression of Profilin 2 inhibits endocytosis, whereas lack of Profilin 2 in neurons results in an increase in endocytosis and membrane recycling. Phosphatidylinositol 4,5-bisphosphate releases Profilin 2 from the Profilin 2-dynamin 1 complex as well as from the Profilin 2-actin complex, suggesting that Profilin 2 is diverging the phosphoinositide signaling pathway to actin polymerization as well as endocytosis.
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Profilin i is essential for cell survival and cell division in early mouse development
Proceedings of the National Academy of Sciences of the United States of America, 2001Co-Authors: Walter Witke, James D. Sutherland, Arlene H Sharpe, Maya Arai, David J KwiatkowskiAbstract:Profilins are thought to play a central role in the regulation of de novo actin assembly by preventing spontaneous actin polymerization through the binding of actin monomers, and the adding of monomeric actin to the barbed actin-filament ends. Other cellular functions of Profilin in membrane trafficking and lipid based signaling are also likely. Binding of Profilins to signaling molecules such as Arp2/3 complex, Mena, VASP, N-WASP, dynamin I, and others, further implicates Profilin and actin as regulators of diverse motile activities. In mouse, two Profilins are expressed from two distinct genes. Profilin I is expressed at high levels in all tissues and throughout development, whereas Profilin II is expressed in neuronal cells. To examine the function of Profilin I in vivo, we generated a null Profilin I (pfn1(ko)) allele in mice. Homozygous pfn1(ko/ko) mice are not viable. Pfn1(ko/ko) embryos died as early as the two-cell stage, and no pfn1(ko/ko) blastocysts were detectable. Adult pfn1(ko/wt) mice show a 50% reduction in Profilin I expression with no apparent impairment of cell function. However, pfn1(ko/wt) embryos have reduced survival during embryogenesis compared with wild type. Although weakly expressed in early embryos, Profilin II cannot compensate for lack of Profilin I. Our results indicate that mouse Profilin I is an essential protein that has dosage-dependent effects on cell division and survival during embryogenesis.
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Alternative splicing of the mouse Profilin II gene generates functionally different Profilin isoforms.
Journal of Cell Science, 2000Co-Authors: A. Di Nardo, David J Kwiatkowski, R. Gareus, Walter WitkeAbstract:Profilins are a conserved family of proteins participating in actin dynamics and cell motility. In the mouse, two Profilin genes are known. Profilin I is expressed universally at high levels, while Profilin II is expressed mainly in the brain. Here we describe the occurrence of two mouse Profilin II isoforms, A and B, which are derived by alternative splicing. They are identical through residue 107 of the protein, but then have distinct C-terminal sequences. Profilin IIA binds to poly-L-proline and actin with high affinity similar to Profilin I. Profilin IIB on the other hand does not bind to actin and the affinity for poly-L-proline is greatly diminished. However, tubulin was found to bind to GST-Profilin IIB, and in vivo GFP-Profilin IIB was recruited to spindles and asters during mitosis in HeLa cells. Our results indicate unexpected diversity in the functions of the Profilin family of proteins, and suggest that in mouse Profilin IIA is intimately involved in actin dynamics, while Profilin IIB associates with other cytoskeletal components.
Brigitte M. Jockusch - One of the best experts on this subject based on the ideXlab platform.
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fine tuning of neuronal architecture requires two Profilin isoforms
Proceedings of the National Academy of Sciences of the United States of America, 2010Co-Authors: Kristin Michaelsen, Martin Rothkegel, Brigitte M. Jockusch, Kai Murk, Marta Zagrebelsky, Anita Dreznjak, Martin KorteAbstract:Two Profilin isoforms (PFN1 and PFN2a) are expressed in the mammalian brain. Although Profilins are essential for regulating actin dynamics in general, the specific role of these isoforms in neurons has remained elusive. We show that knockdown of the neuron-specific PFN2a results in a significant reduction in dendrite complexity and spine numbers of hippocampal neurons. Overexpression of PFN1 in PFN2a-deficient neurons prevents the loss of spines but does not restore dendritic complexity. Furthermore, we show that Profilins are involved in differentially regulating actin dynamics downstream of the pan-neurotrophin receptor (p75NTR), a receptor engaged in modulating neuronal morphology. Overexpression of PFN2a restores the morphological changes in dendrites caused by p75NTR overexpression, whereas PFN1 restores the normal spine density. Our data assign specific functions to the two PFN isoforms, possibly attributable to different affinities for potent effectors also involved in actin dynamics, and suggest that they are important for the signal-dependent fine-tuning of neuronal architecture.
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The profile of Profilins
Reviews of physiology biochemistry and pharmacology, 2007Co-Authors: Brigitte M. Jockusch, Kai Murk, Martin RothkegelAbstract:Profilins are small proteins involved in actin dynamics. In accordance with this function, they are found in all eukaryotes and are structurally highly conserved. However, their precise role in regulating actin-related functions is just beginning to emerge. This article recapitulates the wealth of information on structure, expression and functions accumulated on Profilins from many different organisms in the 30 years after their discovery as actin-binding proteins. Emphasis is given to their interaction with a plethora of many different ligands in the cytoplasm as well as in the nucleus, which is considered the basis for their various activities and the significance of the tissue-specific expression of Profilin isoforms.
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a role for polyproline motifs in the spinal muscular atrophy protein smn Profilins bind to and colocalize with smn in nuclear gems
Journal of Biological Chemistry, 1999Co-Authors: Torsten Giesemann, Martin Rothkegel, Brigitte M. Jockusch, Silvia Rathkehartlieb, Jorg W Bartsch, Sabine Buchmeier, Harald JockuschAbstract:Next Section Abstract Spinal muscular atrophy (SMA) is an autosomal recessive disorder characterized by the loss of α-motoneurons in the spinal cord followed by atrophy of skeletal muscles. SMA-determining candidate genes, SMN1 and SMN2, have been identified on human chromosome 5q. The corresponding SMN protein is expressed ubiquitously. It is coded by seven exons and contains conspicuous proline-rich motifs in its COOH-terminal third (exons 4, 5, and 6). Such motifs are known to bind to Profilins (PFNs), small proteins engaged in the control of actin dynamics. We tested whether Profilins interact with SMN via its polyproline stretches. Using the yeast two-hybrid system we show that Profilins bind to SMN and that this binding depends on its proline-rich motifs. These results were confirmed by coimmunoprecipitation and by in vitro binding studies. Two PFN isoforms, I and II, are known, of which II is characteristic for central nervous system tissue. We show by in situ hybridization that both PFNs are highly expressed in mouse spinal cord and that PFN II is expressed predominantly in neurons. In motoneurons, the primary target of neurodegeneration in SMA, Profilins are highly concentrated and colocalize with SMN in the cytoplasm of the cell body and in nuclear gems. Likewise, SMN and PFN I colocalize in gems of HeLa cells. Although SMN interacts with both Profilin isoforms, binding of PFN II was stronger than of PFN I in all assays employed. Because the SMN genes are expressed ubiquitously, our findings suggest that the interaction of PFN II with SMN may be involved in neuron-specific effects of SMN mutations.
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Differential colocalization of Profilin with microfilaments in PtK2 cells
Cell motility and the cytoskeleton, 1997Co-Authors: Oleg A. Mayboroda, Kathrin Schluter, Brigitte M. JockuschAbstract:Profilins are thought to be involved in the control of actin dynamics in eukaryotic cells. In accordance with this concept, Profilin was found to be colocalized with the cortical microfilament webs in leading lamellae of locomoting and spreading fibroblasts. However, so far, there is little information on the distribution of Profilin in other cell types. In this study, we report on the colocalization of Profilin with various microfilament suprastructures in the epithelial cell line PtK2. This cell line, which is derived from rat kangaroo, contains a Profilin sharing an N-terminal epitope with bovine and human Profilin I, as seen by immunoblotting with monoclonal antibodies. By using immunofluorescence in conjunction with conventional fluorescence microscopy and confocal laser-scanning microscopy, we found Profilin in ruffling areas of the peripheral lamellae and nascent stress fibers of spreading cells, whereas the peripheral belts of stationary cells growing in epithelioid sheets lacked Profilin staining. In these cells, Profilin was primarily distributed in a fine reticular or vesicular network that was not related to the microfilament system. Conspicuously low levels of Profilins was not related to the contractile ring of mitotic cells. This was found for different fixation protocols and antibodies of the IgG and IgM type, respectively, indicating that lack of staining of the cleavage furrow was not due to antibody penetration problems. Depending on the fixation protocol, the nuclear matrix appeared strongly positive or negative for Profilin. Cells microinjected with birch pollen Profilin and labeled with a birch Profilin-specific monoclonal antibody corroborated the results obtained with the endogeneous protein: The injected Profilin was targeted to the cortical web and to nascent stress fibers of spreading cells but not to the cleavage ring of mitotic cells. These results suggest that high concentrations of a Profilin I homologue are preferentially located with those microfilament suprastructures in PtK2 cells that are subject to rapid modulation by external signals.
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the proline rich focal adhesion and microfilament protein vasp is a ligand for Profilins
The EMBO Journal, 1995Co-Authors: Matthias Reinhard, Brigitte M. Jockusch, K Giehl, K Abel, C Haffner, Thomas Jarchau, V Hoppe, Ulrich WalterAbstract:Profilins are small proteins that form complexes with G-actin and phosphoinositides and are therefore considered to link the microfilament system to signal transduction pathways. In addition, they bind to poly-L-proline, but the biological significance of this interaction is not yet known. The recent molecular cloning of the vasodilator-stimulated phosphoprotein (VASP), an established in vivo substrate of cAMP- and cGMP-dependent protein kinases, revealed the presence of a proline-rich domain which prompted us to investigate a possible interaction with Profilins. VASP is a microfilament and focal adhesion associated protein which is also concentrated in highly dynamic regions of the cell cortex. Here, we demonstrate that VASP is a natural proline-rich Profilin ligand. Human platelet VASP bound directly to purified Profilins from human platelets, calf thymus and birch pollen. Moreover, VASP and a novel protein were specifically extracted from total cell lysates by Profilin affinity chromatography and subsequently eluted either with poly-L-proline or a peptide corresponding to a proline-rich VASP motif. Finally, the subcellular distributions of VASP and Profilin suggest that both proteins also interact within living cells. Our data support the hypothesis that Profilin and VASP act in concert to convey signal transduction to actin filament formation.
Anja Lambrechts - One of the best experts on this subject based on the ideXlab platform.
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On the origin and evolution of vertebrate and viral Profilins.
FEBS letters, 2006Co-Authors: Debby Polet, Anja Lambrechts, Klaas Vandepoele, Joël Vandekerckhove, Christophe AmpeAbstract:The three dimensional structures of Profilins from invertebrates and vertebrates are remarkably similar despite low sequence similarity. Their evolutionary relationship remains thus enigmatic. A phylogenetic analysis of Profilins from Deuterostoma indicates that Profilin III and IV isoforms each form distinct groups. Profilin IV is most related to invertebrate Profilins and originated prior to vertebrate evolution whereas separation of Profilin I, II and III isoforms occurred early in vertebrate evolution. Viral Profilins are most similar to Profilin III. In silico analysis of representative Profilin gene structures corroborates the phylogenetic result and we discuss this in terms of biochemical differences.
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a role for complexes of survival of motor neurons smn protein with gemins and Profilin in neurite like cytoplasmic extensions of cultured nerve cells
Experimental Cell Research, 2005Co-Authors: Aarti Sharma, Anja Lambrechts, Christophe Ampe, Le Thi Hao, Caroline Sewry, Arthur H M Burghes, Glenn E MorrisAbstract:Abstract Spinal muscular atrophy (SMA) is caused by reduced levels of SMN (survival of motor neurons protein) and consequent loss of motor neurons. SMN is involved in snRNP transport and nuclear RNA splicing, but axonal transport of SMN has also been shown to occur in motor neurons. SMN also binds to the small actin-binding protein, Profilin. We now show that SMN and Profilin II co-localise in the cytoplasm of differentiating rat PC12 cells and in neurite-like extensions, especially at their growth cones. Many components of known SMN complexes were also found in these extensions, including gemin2 (SIP-1), gemin6, gemin7 and unrip (unr-interacting protein). Coilin p80 and Sm core protein immunoreactivity, however, were seen only in the nucleus. SMN is known to associate with β-actin mRNA and specific hnRNPs in axons and in neurite extensions of cultured nerve cells, and SMN also stimulates neurite outgrowth in cultures. Our results are therefore consistent with SMN complexes, rather than SMN alone, being involved in the transport of actin mRNPs along the axon as in the transport of snRNPs into the nucleus by similar SMN complexes. Antisense knockdown of Profilin I and II isoforms inhibited neurite outgrowth of PC12 cells and caused accumulation of SMN and its associated proteins in cytoplasmic aggregates. BIAcore studies demonstrated a high affinity interaction of SMN with Profilin IIa, the isoform present in developing neurons. Pathogenic missense mutations in SMN, or deletion of exons 5 and 7, prevented this interaction. The interaction is functional in that SMN can modulate actin polymerisation in vitro by reducing the inhibitory effect of Profilin IIa. This suggests that reduced SMN in SMA might cause axonal pathfinding defects by disturbing the normal regulation of microfilament growth by Profilins.
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Profilin II is alternatively spliced, resulting in Profilin isoforms that are differentially expressed and have distinct biochemical properties.
Molecular and cellular biology, 2000Co-Authors: Anja Lambrechts, Attila Braun, Attila Aszódi, Joël Vandekerckhove, Veronique Jonckheere, Lorene M. Lanier, Johan Robbens, Inge Van Colen, Reinhard Fässler, Christophe AmpeAbstract:We deduced the structure of the mouse Profilin II gene. It contains five exons that can generate four different transcripts by alternative splicing. Two transcripts encode different Profilin II isoforms (designated IIa and IIb) that have similar affinities for actin but different affinities for polyphosphoinositides and proline-rich sequences. Profilins IIa and IIb are also present in humans, suggesting that all mammals have three Profilin isoforms. Profilin I is the major form in all tissues, except in the brain, where Profilin IIa is most abundant. Profilin IIb appears to be a minor form, and its expression is restricted to a limited number of tissues, indicating that the alternative splicing is tightly regulated. Western blotting and whole-mount in situ hybridization show that, in contrast to the expression of Profilin I, the expression level of Profilin IIa is developmentally regulated. In situ hybridization of adult brain sections reveals overlapping expression patterns of Profilins I and IIa.
