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Mark A. Lemmon - One of the best experts on this subject based on the ideXlab platform.
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loss of Pleckstrin defines a novel pathway for pkc mediated exocytosis
Blood, 2009Co-Authors: Lurong Lian, Mark A. Lemmon, Yanfeng Wang, Matthew J Flick, John K Choi, Edward W Scott, Jay L Degen, Charles S AbramsAbstract:Pleckstrin, the platelet and leukocyte C kinase substrate, is a prominent substrate of PKC in platelets, monocytes, macrophages, lymphocytes, and granulocytes. Pleckstrin accounts for 1% of the total protein in these cells, but it is best known for containing the 2 prototypic Pleckstrin homology, or PH, domains. Overexpressed Pleckstrin can affect polyphosphoinositide second messenger–based signaling events; however, its true in vivo role has been unknown. Here, we describe mice containing a null mutation within the Pleckstrin gene. Platelets lacking Pleckstrin exhibit a marked defect in exocytosis of δ and α granules, αIIbβ3 activation, actin assembly, and aggregation after exposure to the PKC stimulant, PMA. Pleckstrin-null platelets aggregate normally in response to thrombin, but they fail to aggregate in response to thrombin in the presence of PI3K inhibitors, suggesting that a PI3K-dependent signaling pathway compensates for the loss of Pleckstrin. Although Pleckstrin-null platelets merged their granules in response to stimulation of PKC, they failed to empty their contents into the open canalicular system. This might be attributable to impaired actin assembly present in cells lacking Pleckstrin. These data show that Pleckstrin regulates the fusion of granules to the cell membrane and is an essential component of PKC-mediated exocytosis.
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membrane recognition by phospholipid binding domains
Nature Reviews Molecular Cell Biology, 2008Co-Authors: Mark A. LemmonAbstract:Many different globular domains bind to the surfaces of cellular membranes, or to specific phospholipid components in these membranes, and this binding is often tightly regulated. Examples include Pleckstrin homology and C2 domains, which are among the largest domain families in the human proteome. Crystal structures, binding studies and analyses of subcellular localization have provided much insight into how members of this diverse group of domains bind to membranes, what features they recognize and how binding is controlled. A full appreciation of these processes is crucial for understanding how protein localization and membrane topography and trafficking are regulated in cells.
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Pleckstrin homology (PH) domains and phosphoinositides.
Biochemical Society symposium, 2007Co-Authors: Mark A. LemmonAbstract:PH (Pleckstrin homology) domains represent the 11th most common domain in the human proteome. They are best known for their ability to bind phosphoinositides with high affinity and specificity, although it is now clear that less than 10% of all PH domains share this property. Cases in which PH domains bind specific phosphoinositides with high affinity are restricted to those phosphoinositides that have a pair of adjacent phosphates in their inositol headgroup. Those that do not [PtdIns3P, PtdIns5P and PtdIns(3,5)P2] are instead recognized by distinct classes of domains including FYVE domains, PX (phox homology) domains, PHD (plant homeodomain) fingers and the recently identified PROPPINs (b-propellers that bind polyphosphoinositides). Of the 90% of PH domains that do not bind strongly and specifically to phosphoinositides, few are well understood. One group of PH domains appears to bind both phosphoinositides (with little specificity) and Arf (ADP-ribosylation factor) family small G-proteins, and are targeted to the Golgi apparatus where both phosphoinositides and the relevant Arfs are both present. Here, the PH domains may function as coincidence detectors. A central challenge in understanding the majority of PH domains is to establish whether the very low affinity phosphoinositide binding reported in many cases has any functional relevance. For PH domains from dynamin and from Dbl family proteins, this weak binding does appear to be functionally important, although its precise mechanistic role is unclear. In many other cases, it is quite likely that alternative binding partners are more relevant, and that the observed PH domain homology represents conservation of structural fold rather than function.
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Pleckstrin homology domains: not just for phosphoinositides
Biochemical Society Transactions, 2004Co-Authors: Mark A. LemmonAbstract:PH domains (Pleckstrin homology domains) are the 11th most common domain in the human genome and are best known for their ability to target cellular membranes by binding specifically to phosphoinositides. Recent studies in yeast have shown that, in fact, this is a property of only a small fraction of the known PH domains. Most PH domains are not capable of independent membrane targeting, and those capable of doing so (approx. 33%) appear, most often, to require both phosphoinositide and non-phosphoinositide determinants for their subcellular localization. Several recent studies have suggested that small GTPases such as ARF family proteins play a role in defining PH domain localization. Some others have described a signalling role for PH domains in regulating small GTPases, although phosphoinositides may also play a role. These findings herald a change in our perspective of PH domain function, which will be significantly more diverse than previously supposed.
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Pleckstrin homology domains and the cytoskeleton
FEBS letters, 2001Co-Authors: Mark A. Lemmon, Kathryn M Ferguson, Charles S AbramsAbstract:Pleckstrin homology (PH) domains are 100–120 amino acid protein modules best known for their ability to bind phosphoinositides. All possess an identical core β-sandwich fold and display marked electrostatic sidedness. The binding site for phosphoinositides lies in the center of the positively charged face. In some cases this binding site is well defined, allowing highly specific and strong ligand binding. In several of these cases the PH domains specifically recognize 3-phosphorylated phosphoinositides, allowing them to drive membrane recruitment in response to phosphatidylinositol 3-kinase activation. Examples of these PH domain-containing proteins include certain Dbl family guanine nucleotide exchange factors, protein kinase B, PhdA, and Pleckstrin-2. PH domain-mediated membrane recruitment of these proteins contributes to regulated actin assembly and cell polarization. Many other PH domain-containing cytoskeletal proteins, such as spectrin, have PH domains that bind weakly, and to all phosphoinositides. In these cases, the individual phosphoinositide interactions may not be sufficient for membrane association, but appear to require self-assembly of their host protein and/or cooperation with other anchoring motifs within the same molecule to drive membrane attachment.
Stephen W Fesik - One of the best experts on this subject based on the ideXlab platform.
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Structure and ligand recognition of the phosphotyrosine binding domain of Shc.
Nature, 1995Co-Authors: Ming-ming Zhou, Kodimangalam S. Ravichandran, Warren S. Wade, John E. Harlan, Edward T Olejniczak, Robert P Meadows, Andrew M. Petros, Michael Sattler, Steven J Burakoff, Stephen W FesikAbstract:The nuclear magnetic resonance structure of the phosphotyrosine binding (PTB) domain of She complexed to a phosphopeptide reveals an alternative means of recognizing tryosine-phosphorylated proteins. Unlike in SH2 domains, the phosphopeptide forms an antiparallel β-strand with a β-sheet of the protein, interacts with a hydrophobic pocket through the (pY–5) residue, and adopts a β-turn. The PTB domain is structurally similar to Pleckstrin homology domains (a β-sandwich capped by an α-helix) and binds to acidic phospholipids, suggesting a possible role in membrane localization.
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Structural characterization of the interaction between a Pleckstrin homology domain and phosphatidylinositol 4,5-bisphosphate.
Biochemistry, 1995Co-Authors: John E. Harlan, Ho Sup Yoon, Philip J. Hajduk, Stephen W FesikAbstract:The Pleckstrin homology (PH) domain is a protein module of approximately 100 amino acids that is found in several proteins involved in signal transduction [for a recent review, see Gibson et al. (1994) Trends Biochem. Sci. 19, 349-353]. Although the specific function of the PH domain has not yet been elucidated, many of the proteins which contain this domain associate with phospholipid membranes, and PH domains have been shown to bind to phosphatidylinositol 4,5-bisphosphate (PIP2) [Harlan et al. (1994) Nature 371, 168-170] and the beta gamma subunits of G-proteins [Touhara et al. (1994) J. Biol. Chem. 269, 10217-10220]. We have postulated that Pleckstrin homology domains may be important for the translocation of proteins to the membrane by an interaction with the negatively charged head group of phospholipids. Here we show the importance of three conserved lysine residues for binding to PIP2 by site-directed mutagenesis. These results should aid future site-directed mutagenesis studies in probing the function of PIP2-PH domain interactions in the various proteins containing this module. In addition, we examine the specificity of this binding and illustrate the importance of charge--charge interactions in PIP2-PH domain complex formation from binding experiments involving PIP2 analogs.
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Pleckstrin homology domains bind to phosphatidylinositol 4 5 bisphosphate
Nature, 1994Co-Authors: John E. Harlan, Ho Sup Yoon, Philip J. Hajduk, Stephen W FesikAbstract:THE Pleckstrin homology (PH) domain is a new protein module of around 100 amino acids found in several proteins involved in signal transduction1–5. Although its specific function has yet to be elucidated, the carboxy-terminal regions of many βγ domains bind to the py subunits of G proteins6,7. On the basis of structural similarities between PH domains and lipid-binding proteins, we have proposed that PH domains may be binding to lipophilic molecules8. Indeed, many of the proteins that contain this domain associate with phospholipid membranes6,9,10, and disruption of this domain can interfere with membrane association6,11. Here we report that PH domains bind to phosphatidylinositol-4,5-bisphosphate and show that the lipid-binding site is located at the lip of the β-barrel. This suggests that PH domains may be important for membrane localization of proteins through interactions with phosphatidylinositol-4,5-bisphosphate.
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Solution structure of a Pleckstrin-homology domain.
Nature, 1994Co-Authors: Ho Sup Yoon, Edward T Olejniczak, Robert P Meadows, Andrew M. Petros, Philip J. Hajduk, Stephen W FesikAbstract:Pleckstrin, the major protein kinase C substrate of platelets, contains domains of about 100 amino acids at the amino and carboxy termini that have been found in a number of proteins, including serine/threonine kinases, GTPase-activating proteins, phospholipases and cytoskeletal proteins. These conserved sequences, termed Pleckstrin-homology (PH) domains, are thought to be involved in signal transduction. But the details of the function and binding partners of the PH domains have not been characterized. Here we report the solution structure of the N-terminal Pleckstrin-homology domain of Pleckstrin determined using heteronuclear three-dimensional nuclear magnetic resonance spectroscopy. The structure consists of an up-and-down beta-barrel of seven antiparallel beta-strands and a C-terminal amphiphilic alpha-helix that caps one end of the barrel. The overall topology of the domain is similar to that of the retinol-binding protein family of structures.
Hartmut Oschkinat - One of the best experts on this subject based on the ideXlab platform.
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automated noesy interpretation with ambiguous distance restraints the refined nmr solution structure of the Pleckstrin homology domain from beta spectrin
Journal of Molecular Biology, 1997Co-Authors: Michael Nilges, Maria J Macias, Sean I Odonoghue, Hartmut OschkinatAbstract:We have used a novel, largely automated, calculation method to refine the NMR solution structure of the Pleckstrin homology domain of β-spectrin. The method is called ARIA for Ambiguous Restraints for Iterative Assignment. The starting point for ARIA is an almost complete assignment of the proton chemical shifts, and a list of partially assigned NOEs, mostly sequential and secondary structure NOEs. The restraint list is then augmented by automatically interpreting peak lists generated by automated peak-picking. The central task of ARIA is the assignment of ambiguous NOEs during the structure calculation using a combination of ambiguous distance restraints and an iterative assignment strategy. In addition, ARIA calibrates ambiguous NOEs to derive distance restraints, merges overlapping data sets to remove duplicate information, and uses empirical rules to identify erroneous peaks. While the distance restraints for the structure calculations were exclusively extracted from homonuclear 2D experiments, ARIA is especially suited for the analysis of multidimensional spectra. Applied to the Pleckstrin homology domain, ARIA generated structures of good quality, and of sufficiently high accuracy to solve the X-ray crystal structure of the same domain by molecular replacement. The comparison of the free NMR solution structure to the X-ray structure, which is complexed to d-myo-inositol-1,4,5-triphosphate, shows that the ligand primarily induces a disorder-order transition in the binding loops, which are disordered in the NMR ensemble but well ordered in the crystal. The structural core of the protein is unaffected, as evidenced by a backbone root-mean-square difference between the average NMR coordinates and the X-ray crystal structure for the secondary structure elements of less than 0.6 A.
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automated noesy interpretation with ambiguous distance restraints the refined nmr solution structure of the Pleckstrin homology domain from beta spectrin
Journal of Molecular Biology, 1997Co-Authors: Michael Nilges, Maria J Macias, Sean I Odonoghue, Hartmut OschkinatAbstract:We have used a novel, largely automated, calculation method to refine the NMR solution structure of the Pleckstrin homology domain of beta-spectrin. The method is called ARIA for Ambiguous Restraints for Iterative Assignment. The starting point for ARIA is an almost complete assignment of the proton chemical shifts, and a list of partially assigned NOEs, mostly sequential and secondary structure NOEs. The restraint list is then augmented by automatically interpreting peak lists generated by automated peak-picking. The central task of ARIA is the assignment of ambiguous NOEs during the structure calculation using a combination of ambiguous distance restraints and an iterative assignment strategy. In addition, ARIA calibrates ambiguous NOEs to derive distance restraints, merges overlapping data sets to remove duplicate information, and uses empirical rules to identify erroneous peaks. While the distance restraints for the structure calculations were exclusively extracted from homonuclear 2D experiments, ARIA is especially suited for the analysis of multidimensional spectra. Applied to the Pleckstrin homology domain, ARIA generated structures of good quality, and of sufficiently high accuracy to solve the X-ray crystal structure of the same domain by molecular replacement. The comparison of the free NMR solution structure to the X-ray structure, which is complexed to D-myo-inositol-1,4,5-triphosphate, shows that the ligand primarily induces a disorder-order transition in the binding loops, which are disordered in the NMR ensemble but well ordered in the crystal. The structural core of the protein is unaffected, as evidenced by a backbone root-mean-square difference between the average NMR coordinates and the X-ray crystal structure for the secondary structure elements of less than 0.6 A.
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structure of the Pleckstrin homology domain from beta spectrin
Nature, 1994Co-Authors: Maria J Macias, Michael Nilges, Andrea Musacchio, Hannes Ponstingl, Matti Saraste, Hartmut OschkinatAbstract:THE ‘Pleckstrin homology’ or PH domain is a 100-residue protein module. It is present in many kinases, different isoforms of phospholipase C, GTPase-activating proteins and nucleotide-exchange factors1–4. Its function is not known, but many proteins that contain a PH domain interact with GTP-binding proteins5. The PH domain in β-adrenergic receptor kinase may be involved in binding to the βγ subunits of a trimeric G-protein3, 4, 6, 7. We report here the three-dimensional structure of the PH domain of the cytoskeletal protein spectrin using homonuclear nuclear magnetic resonance. The core of the molecule is an antiparallel β-sheet consisting of seven strands. The C terminus is folded into a long α-helix, and another helix is present in one of the surface loops. The molecule is electrostatically polarized and contains a pocket which may be involved in the binding of a ligand. There is a distant relationship to the peptidyl-prolyl-cis-trans-isomerase FKBP in which this pocket is involved in the binding of the macrocyclic compound FK506(refs 8–11).
Kathryn M Ferguson - One of the best experts on this subject based on the ideXlab platform.
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Pleckstrin homology domains and the cytoskeleton
FEBS letters, 2001Co-Authors: Mark A. Lemmon, Kathryn M Ferguson, Charles S AbramsAbstract:Pleckstrin homology (PH) domains are 100–120 amino acid protein modules best known for their ability to bind phosphoinositides. All possess an identical core β-sandwich fold and display marked electrostatic sidedness. The binding site for phosphoinositides lies in the center of the positively charged face. In some cases this binding site is well defined, allowing highly specific and strong ligand binding. In several of these cases the PH domains specifically recognize 3-phosphorylated phosphoinositides, allowing them to drive membrane recruitment in response to phosphatidylinositol 3-kinase activation. Examples of these PH domain-containing proteins include certain Dbl family guanine nucleotide exchange factors, protein kinase B, PhdA, and Pleckstrin-2. PH domain-mediated membrane recruitment of these proteins contributes to regulated actin assembly and cell polarization. Many other PH domain-containing cytoskeletal proteins, such as spectrin, have PH domains that bind weakly, and to all phosphoinositides. In these cases, the individual phosphoinositide interactions may not be sufficient for membrane association, but appear to require self-assembly of their host protein and/or cooperation with other anchoring motifs within the same molecule to drive membrane attachment.
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signal dependent membrane targeting by Pleckstrin homology ph domains
Biochemical Journal, 2000Co-Authors: Mark A. Lemmon, Kathryn M FergusonAbstract:Pleckstrin homology (PH) domains are small protein modules of around 120 amino acids found in many proteins involved in cell signalling, cytoskeletal rearrangement and other processes. Although several different protein ligands have been proposed for PH domains, their only clearly demonstrated physiological function to date is to bind membrane phosphoinositides. The PH domain from phospholipase C-δ 1 binds specifically to PtdIns(4,5) P 2 and its headgroup, and has become a valuable tool for studying cellular PtdIns(4,5) P 2 functions. More recent developments have demonstrated that a subset of PH domains recognizes the products of agonist-stimulated phosphoinositide 3-kinases. Fusion of these PH domains to green fluorescent protein has allowed dramatic demonstrations of their independent ability to drive signal-dependent recruitment of their host proteins to the plasma membrane. We discuss the structural basis for this 3-phosphoinoistide recognition and the role that it plays in cellular signalling. PH domains that bind specifically to phosphoinositides comprise only a minority (perhaps 15%) of those known, raising questions as to the physiological role of the remaining 85% of PH domains. Most (if not all) PH domains bind weakly and non-specifically to phosphoinositides. Studies of dynamin-1 have indicated that oligomerization of its PH domain may be important in driving membrane association. We discuss the possibility that membrane targeting by PH domains with low affinity for phosphoinositides could be driven by alteration of their oligomeric state and thus the avidity of their membrane binding.
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Signal-dependent membrane targeting by Pleckstrin homology (PH) domains
Biochemical Journal, 2000Co-Authors: Mark A. Lemmon, Kathryn M FergusonAbstract:Pleckstrin homology (PH) domains are small protein modules of around 120 amino acids found in many proteins involved in cell signalling, cytoskeletal rearrangement and other processes. Although several different protein ligands have been proposed for PH domains, their only clearly demonstrated physiological function to date is to bind membrane phosphoinositides. The PH domain from phospholipase C-delta(1) binds specifically to PtdIns(4,5)P(2) and its headgroup, and has become a valuable tool for studying cellular PtdIns(4,5)P(2) functions. More recent developments have demonstrated that a subset of PH domains recognizes the products of agonist-stimulated phosphoinositide 3-kinases. Fusion of these PH domains to green fluorescent protein has allowed dramatic demonstrations of their independent ability to drive signal-dependent recruitment of their host proteins to the plasma membrane. We discuss the structural basis for this 3-phosphoinoistide recognition and the role that it plays in cellular signalling. PH domains that bind specifically to phosphoinositides comprise only a minority (perhaps 15%) of those known, raising questions as to the physiological role of the remaining 85% of PH domains. Most (if not all) PH domains bind weakly and non-specifically to phosphoinositides. Studies of dynamin-1 have indicated that oligomerization of its PH domain may be important in driving membrane association. We discuss the possibility that membrane targeting by PH domains with low affinity for phosphoinositides could be driven by alteration of their oligomeric state and thus the avidity of their membrane binding.
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structural basis for discrimination of 3 phosphoinositides by Pleckstrin homology domains
Molecular Cell, 2000Co-Authors: Kathryn M Ferguson, Jennifer M Kavran, Steven J Isakoff, Edward Y Skolnik, Vijay G Sankaran, Emmanuel Fournier, Mark A. LemmonAbstract:Pleckstrin homology (PH) domains are protein modules of around 120 amino acids found in many proteins involved in cellular signaling. Certain PH domains drive signal-dependent membrane recruitment of their host proteins by binding strongly and specifically to lipid second messengers produced by agonist-stimulated phosphoinositide 3-kinases (PI 3-Ks). We describe X-ray crystal structures of two different PH domains bound to Ins(1,3,4,5)P4, the head group of the major PI 3-K product PtdIns(3,4,5)P3. One of these PH domains (from Grp1) is PtdIns(3,4,5)P3 specific, while the other (from DAPP1/PHISH) binds strongly to both PtdIns(3,4,5)P3 and its 5'-dephosphorylation product, PtdIns(3,4)P2. Comparison of the two structures provides an explanation for the distinct phosphoinositide specificities of the two PH domains and allows us to predict the 3-phosphoinositide selectivity of uncharacterized PH domains.
Michael Nilges - One of the best experts on this subject based on the ideXlab platform.
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automated noesy interpretation with ambiguous distance restraints the refined nmr solution structure of the Pleckstrin homology domain from beta spectrin
Journal of Molecular Biology, 1997Co-Authors: Michael Nilges, Maria J Macias, Sean I Odonoghue, Hartmut OschkinatAbstract:We have used a novel, largely automated, calculation method to refine the NMR solution structure of the Pleckstrin homology domain of β-spectrin. The method is called ARIA for Ambiguous Restraints for Iterative Assignment. The starting point for ARIA is an almost complete assignment of the proton chemical shifts, and a list of partially assigned NOEs, mostly sequential and secondary structure NOEs. The restraint list is then augmented by automatically interpreting peak lists generated by automated peak-picking. The central task of ARIA is the assignment of ambiguous NOEs during the structure calculation using a combination of ambiguous distance restraints and an iterative assignment strategy. In addition, ARIA calibrates ambiguous NOEs to derive distance restraints, merges overlapping data sets to remove duplicate information, and uses empirical rules to identify erroneous peaks. While the distance restraints for the structure calculations were exclusively extracted from homonuclear 2D experiments, ARIA is especially suited for the analysis of multidimensional spectra. Applied to the Pleckstrin homology domain, ARIA generated structures of good quality, and of sufficiently high accuracy to solve the X-ray crystal structure of the same domain by molecular replacement. The comparison of the free NMR solution structure to the X-ray structure, which is complexed to d-myo-inositol-1,4,5-triphosphate, shows that the ligand primarily induces a disorder-order transition in the binding loops, which are disordered in the NMR ensemble but well ordered in the crystal. The structural core of the protein is unaffected, as evidenced by a backbone root-mean-square difference between the average NMR coordinates and the X-ray crystal structure for the secondary structure elements of less than 0.6 A.
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automated noesy interpretation with ambiguous distance restraints the refined nmr solution structure of the Pleckstrin homology domain from beta spectrin
Journal of Molecular Biology, 1997Co-Authors: Michael Nilges, Maria J Macias, Sean I Odonoghue, Hartmut OschkinatAbstract:We have used a novel, largely automated, calculation method to refine the NMR solution structure of the Pleckstrin homology domain of beta-spectrin. The method is called ARIA for Ambiguous Restraints for Iterative Assignment. The starting point for ARIA is an almost complete assignment of the proton chemical shifts, and a list of partially assigned NOEs, mostly sequential and secondary structure NOEs. The restraint list is then augmented by automatically interpreting peak lists generated by automated peak-picking. The central task of ARIA is the assignment of ambiguous NOEs during the structure calculation using a combination of ambiguous distance restraints and an iterative assignment strategy. In addition, ARIA calibrates ambiguous NOEs to derive distance restraints, merges overlapping data sets to remove duplicate information, and uses empirical rules to identify erroneous peaks. While the distance restraints for the structure calculations were exclusively extracted from homonuclear 2D experiments, ARIA is especially suited for the analysis of multidimensional spectra. Applied to the Pleckstrin homology domain, ARIA generated structures of good quality, and of sufficiently high accuracy to solve the X-ray crystal structure of the same domain by molecular replacement. The comparison of the free NMR solution structure to the X-ray structure, which is complexed to D-myo-inositol-1,4,5-triphosphate, shows that the ligand primarily induces a disorder-order transition in the binding loops, which are disordered in the NMR ensemble but well ordered in the crystal. The structural core of the protein is unaffected, as evidenced by a backbone root-mean-square difference between the average NMR coordinates and the X-ray crystal structure for the secondary structure elements of less than 0.6 A.
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structure of the Pleckstrin homology domain from beta spectrin
Nature, 1994Co-Authors: Maria J Macias, Michael Nilges, Andrea Musacchio, Hannes Ponstingl, Matti Saraste, Hartmut OschkinatAbstract:THE ‘Pleckstrin homology’ or PH domain is a 100-residue protein module. It is present in many kinases, different isoforms of phospholipase C, GTPase-activating proteins and nucleotide-exchange factors1–4. Its function is not known, but many proteins that contain a PH domain interact with GTP-binding proteins5. The PH domain in β-adrenergic receptor kinase may be involved in binding to the βγ subunits of a trimeric G-protein3, 4, 6, 7. We report here the three-dimensional structure of the PH domain of the cytoskeletal protein spectrin using homonuclear nuclear magnetic resonance. The core of the molecule is an antiparallel β-sheet consisting of seven strands. The C terminus is folded into a long α-helix, and another helix is present in one of the surface loops. The molecule is electrostatically polarized and contains a pocket which may be involved in the binding of a ligand. There is a distant relationship to the peptidyl-prolyl-cis-trans-isomerase FKBP in which this pocket is involved in the binding of the macrocyclic compound FK506(refs 8–11).