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Michael G. Rossmann - One of the best experts on this subject based on the ideXlab platform.
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Structure of the 3.3 MDa, in vitro assembled, hubless bacteriophage T4 baseplate
Journal of Structural Biology, 2014Co-Authors: Thomas Klose, Fumio Arisaka, Anastasia A. Aksyuk, Pavel Plevka, Xinzheng Zhang, Michael G. RossmannAbstract:Abstract The bacteriophage T4 baseplate is the control center of the virus, where the recognition of an E scherichia coli host by the long tail fibers is translated into a signal to initiate infection. The short tail fibers unfold from the baseplate for firm attachment to the host, followed by shrinkage of the tail sheath that causes the tail tube to enter and cross the periplasmic space ending with injection of the genome into the host. During this process, the 6.5 MDa baseplate changes its structure from a “dome” shape to a “star” shape. An in vitro assembled hubless baseplate has been crystallized. It consists of six copies of the recombinantly expressed trimeric gene product (gp) 10, monomeric gp7, dimeric gp8, dimeric gp6 and monomeric gp53. The diffraction pattern extends, at most, to 4.0 A resolution. The known partial structures of gp10, gp8, and gp6 and their relative position in the baseplate derived from earlier electron microscopy studies were used for molecular replacement. An electron density map has been calculated based on molecular replacement, single isomorphous replacement with anomalous dispersion data and 2-fold non-crystallographic symmetry averaging between two baseplate wedges in the crystallographic asymmetric unit. The current electron density map indicates that there are structural changes in the gp6, gp8, and gp10 oligomers compared to their structures when separately crystallized. Additional density is also visible corresponding to gp7, gp53 and the unknown parts of gp10 and gp6.
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Structure and function of bacteriophage T4
Future Microbiology, 2014Co-Authors: Moh Lan Yap, Michael G. RossmannAbstract:Bacteriophage T4 is the most well-studied member of Myoviridae, the most complex family of tailed phages. T4 assembly is divided into three independent pathways: the head, the tail and the long tail fibers. The prolate head encapsidates a 172 kbp concatemeric dsDNA genome. The 925 Å-long tail is surrounded by the contractile sheath and ends with a hexagonal baseplate. Six long tail fibers are attached to the baseplate's periphery and are the host cell's recognition sensors. The sheath and the baseplate undergo large conformational changes during infection. X-ray crystallography and cryo-electron microscopy have provided structural information on protein-protein and protein-nucleic acid interactions that regulate conformational changes during assembly and infection of Escherichia coli cells.
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The Structure of Gene Product 6 of Bacteriophage T4, the Hinge-Pin of the Baseplate
Structure, 2009Co-Authors: Anastasia A. Aksyuk, Petr G. Leiman, Vadim V. Mesyanzhinov, Mikhail M. Shneider, Michael G. RossmannAbstract:Summary The baseplate of bacteriophage T4 is a multicomponent protein complex, which controls phage attachment to the host. It assembles from six wedges and a central hub. During infection the baseplate undergoes a large conformational change from a dome-shaped to a flat, star-shaped structure. We report the crystal structure of the C-terminal half of gene product (gp) 6 and investigate its motion with respect to the other proteins during the baseplate rearrangement. Six gp6 dimers interdigitate, forming a ring that maintains the integrity of the baseplate in both conformations. One baseplate wedge contains an N-terminal dimer of gp6, whereas neighboring wedges are tied together through the C-terminal dimer of gp6. The dimeric interactions are preserved throughout the rearrangement of the baseplate. However, the hinge angle between the N- and C-terminal parts of gp6 changes by ∼15°, accounting for a 10 A radial increase in the diameter of the gp6 ring.
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Three-dimensional structure of bacteriophage T4 baseplate
Nature Structural & Molecular Biology, 2003Co-Authors: Victor A Kostyuchenko, Petr G. Leiman, Vadim V. Mesyanzhinov, Shuji Kanamaru, Fumio Arisaka, Paul R. Chipman, Mark J. Van Raaij, Michael G. RossmannAbstract:The baseplate of bacteriophage T4 is a multiprotein molecular machine that controls host cell recognition, attachment, tail sheath contraction and viral DNA ejection. We report here the three-dimensional structure of the baseplate–tail tube complex determined to a resolution of 12 A by cryoelectron microscopy. The baseplate has a six-fold symmetric, dome-like structure ∼520 A in diameter and ∼270 A long, assembled around a central hub. A 940 A–long and 96 A–diameter tail tube, coaxial with the hub, is connected to the top of the baseplate. At the center of the dome is a needle-like structure that was previously identified as a cell puncturing device. We have identified the locations of six proteins with known atomic structures, and established the position and shape of several other baseplate proteins. The baseplate structure suggests a mechanism of baseplate triggering and structural transition during the initial stages of T4 infection.
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Structure and location of gene product 8 in the bacteriophage T4 baseplate.
Journal of Molecular Biology, 2003Co-Authors: Petr G. Leiman, Vadim V. Mesyanzhinov, Victor A Kostyuchenko, Paul R. Chipman, Mikhail M. Shneider, Michael G. RossmannAbstract:Shemyakin-OvchinnikovInstitute of BioorganicChemistry, 16/10Miklukho-Maklaya Street117871 Moscow, RussianFederationMany bacteriophages, such as T4, T7, RB49, and f29, have complex, some-times multilayered, tails that facilitate an almost 100% success rate for theviral particles to infect host cells. In bacteriophage T4, there is a baseplate,which is a multiprotein assembly, at the distal end of the contractile tail.The baseplate communicates to the tail that the phage fibers have attachedto the host cell, thereby initiating the infection process. Gene product 8(gp8), whose amino acid sequence consists of 334 residues, is one of atleast 16 different structural proteins that constitute the T4 baseplate andis the sixth baseplate protein whose structure has been determined. A2.0 A˚ resolution X-ray structure of gp8 shows that the two-domain proteinforms a dimer, in which each monomer consists of a three-layered b-sand-wich with two loops, each containing an a-helix at the opposite sides ofthe sandwich. The crystals of gp8 were produced in the presence ofconcentrated chloride and bromide ions, resulting in at least 11 halide-binding sites per monomer. Five halide sites, situated at the N termini ofa-helices, have a protein environment observed in other halide-containingprotein crystal structures. The computer programs EMfit and SITUS wereused to determine the positions of six gp8 dimers within the 12 A˚ resol-ution cryo-electron microscopy image reconstruction of the baseplate-tailtube complex. The gp8 dimers were found to be located in the upperpart of the baseplate outer rim. About 20% of the gp8 surface is involvedin contacts with other baseplate proteins, presumed to be gp6, gp7, andgp10. With the structure determination of gp8, a total of 53% of thevolume of the baseplate has now been interpreted in terms of its atomicstructure.
Christian Cambillau - One of the best experts on this subject based on the ideXlab platform.
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Structural Insights into Lactococcal Siphophage p2 Baseplate Activation Mechanism
Viruses, 2020Co-Authors: Silvia Spinelli, Christian Cambillau, Sylvain Moineau, Denise M. Tremblay, Adeline GouletAbstract:Virulent phages infecting L. lactis, an industry-relevant bacterium, pose a significant risk to the quality of the fermented milk products. Phages of the Skunavirus genus are by far the most isolated lactococcal phages in the cheese environments and phage p2 is the model siphophage for this viral genus. The baseplate of phage p2, which is used to recognize its host, was previously shown to display two conformations by X-ray crystallography, a rested state and an activated state ready to bind to the host. The baseplate became only activated and opened in the presence of Ca2+. However, such an activated state was not previously observed in the virion. Here, using nanobodies binding to the baseplate, we report on the negative staining electron microscopy structure of the activated form of the baseplate directly observed in the p2 virion, that is compatible with the activated baseplate crystal structure. Analyses of this new structure also established the presence of a second distal tail (Dit) hexamer as a component of the baseplate, the topology of which differs largely from the first one. We also observed an uncoupling between the baseplate activation and the tail tip protein (Tal) opening, suggesting an infection mechanism more complex than previously expected.
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Structure of the type VI secretion system TssK–TssF–TssG baseplate subcomplex revealed by cryo-electron microscopy
Nature Communications, 2018Co-Authors: Young-jun Park, Christian Cambillau, Kaitlyn D. Lacourse, Frank Dimaio, Joseph D. Mougous, David VeeslerAbstract:Type VI secretion systems (T6SSs) translocate effectors into target cells and are made of a contractile sheath and a tube docked onto a multi-protein transmembrane complex via a baseplate. Although some information is available about the mechanisms of tail contraction leading to effector delivery, the detailed architecture and function of the baseplate remain unknown. Here, we report the 3.7 Å resolution cryo-electron microscopy reconstruction of an enteroaggregative Escherichia coli baseplate subcomplex assembled from TssK, TssF and TssG. The structure reveals two TssK trimers interact with a locally pseudo-3-fold symmetrical complex comprising two copies of TssF and one copy of TssG. TssF and TssG are structurally related to each other and to components of the phage T4 baseplate and of the type IV secretion system, strengthening the evolutionary relationships among these macromolecular machines. These results, together with bacterial two-hybrid assays, provide a structural framework to understand the T6SS baseplate architecture. Type VI secretion systems (T6SSs) translocate effector proteins into eukaryotic and bacterial recipient cells and are present in many Gram-negative bacteria. Here the authors present the 3.7 Å cryoEM structure of the E.coli T6SS baseplate wedge comprising TssK–TssF–TssG and propose a model for the T6SS baseplate and needle complex.
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Bacteriophage module reshuffling results in adaptive host range as exemplified by the baseplate model of listerial phage A118.
Virology, 2015Co-Authors: Christian CambillauAbstract:Abstract Each phage infects its specific bacterial host strain through highly specific interactions between the baseplate-associated receptor binding protein (RBP) at the tip of the phage tail and the receptor at the host surface. Baseplates incorporate structural core modules, Dit and Tal, largely conserved among phages, and peripheral modules anchoring the RBPs. Exploiting structural information from the HHpred program and EM data from the Bielmann et al. (2015) paper, a molecular model of the A118 phage baseplate was generated from different building blocks. This model implies the occurrence of baseplate module reshuffling and suggests that listerial phage A118 may have been derived from lactococcal phage TP901-1 through host species exchange. With the increase of available viral module structures, modelling phage Baseplates will become easier and more reliant, and will provide insightful information on the nature of the phage host receptor and its mode of recognition.
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Unraveling Lactococcal Phage Baseplate Assembly by Mass Spectrometry
Molecular & Cellular Proteomics, 2011Co-Authors: Dale A. Shepherd, Julie Lichiere, David Veesler, Alison E. Ashcroft, Christian CambillauAbstract:Bacteriophages belonging to the Caudovirales order possess a tail acting as a molecular machine used during infection to recognize the host and ensure high-efficiency genome delivery to the cell cytoplasm. They bear a large and sophisticated multiprotein organelle at their distal tail end, either a baseplate or a tail-tip, which is the control center for infectivity. We report here insights into the baseplate assembly pathways of two lactoccocal phages (p2 and TP901–1) using electrospray ionization-mass spectrometry. Based on our “block cloning” strategy we have expressed large complexes of their Baseplates as well as several significant structural subcomplexes. Previous biophysical characterization using size-exclusion chromatography coupled with on-line light scattering and refractometry demonstrated that the overproduced recombinant proteins interact with each other to form large (up to 1.9 MDa) and stable assemblies. The structures of several of these complexes have been determined by x-ray diffraction or by electron microscopy. In this contribution, we demonstrate that electrospray ionization-mass spectrometry yields accurate mass measurements for the different baseplate complexes studied from which their stoichiometries can be discerned, and that the subspecies observed in the spectra provide valuable information on the assembly mechanisms of these large organelles.
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solution and electron microscopy characterization of lactococcal phage Baseplates expressed in escherichia coli
Journal of Structural Biology, 2010Co-Authors: Valerie Campanacci, David Veesler, Julie Lichiere, Stephanie Blangy, Giuliano Sciara, Sylvain Moineau, Douwe Van Sinderen, Patrick Bron, Christian CambillauAbstract:Abstract We report here the characterization of several large structural protein complexes forming the Baseplates (or part of them) of Siphoviridae phages infecting Lactococcus lactis: TP901-1, Tuc2009 and p2. We revisited a “block cloning” expression strategy and extended this approach to genomic fragments encoding proteins whose interacting partners have not yet been clearly identified. Biophysical characterization of some of these complexes using circular dichroism and size exclusion chromatography, coupled with on-line light scattering and refractometry, demonstrated that the over-produced recombinant proteins interact with each other to form large (up to 1.9 MDa) and stable baseplate assemblies. Some of these complexes were characterized by electron microscopy confirming their structural homogeneity as well as providing a picture of their overall molecular shapes and symmetry. Finally, using these results, we were able to highlight similarities and differences with the well characterized much larger baseplate of the myophage T4.
Mark A Frankle - One of the best experts on this subject based on the ideXlab platform.
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Influence of reverse total shoulder arthroplasty baseplate design on torque and compression relationship.
JSES international, 2020Co-Authors: Miguel A Diaz, Eric T Ricchetti, Grant E Garrigues, Sergio Gutierrez, Mark A FrankleAbstract:A linear relationship between baseplate insertion torque and compression force in reverse shoulder arthroplasty (RSA) Baseplates with central screw design has been recently established. In this study, we evaluated 3 different baseplate designs and their influence on the torque-compression relationship. Three different RSA baseplate designs were evaluated through biomechanical testing using a glenoid vault, bone surrogate model. A digital torque gauge was used to measure insertion torque applied to the baseplate, whereas compression data were collected continuously from a load cell. Additionally, 2 predictive models were developed to predict the compression forces of each baseplate design at varying levels of torque. A linear relationship was found between baseplate compression and insertion torque for all 3 baseplate designs. Both the monoblock and 2-piece locking designs achieved the goal torque of 6.8 Nm, whereas the 2-piece nonlocking design did not due to material strip-out. No significant difference in maximum compression was found between the monoblock and 2-piece locking designs. However, the 2-piece nonlocking design achieved significantly higher compression. Both predictive models were shown to adequately predict compressive forces at different torque inputs for the monoblock and 2-piece locking designs but not the 2-piece nonlocking design. The torque-compression relationship of a central screw baseplate is significantly affected by baseplate design. A 2-piece nonlocking baseplate reaches higher compression levels and risks material strip-out at lower insertional torques compared with a monoblock and 2-piece locking design. This has implications both on component design and on surgeon tactile feedback during surgery. © 2020 The Authors.
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Influence of reverse total shoulder arthroplasty baseplate design on torque and compression relationship
2020Co-Authors: Miguel A Diaz, Eric T Ricchetti, Grant E Garrigues, Sergio Gutierrez, Mark A FrankleAbstract:Background A linear relationship between baseplate insertion torque and compression force in reverse shoulder arthroplasty (RSA) Baseplates with central screw design has been recently established. In this study, we evaluated 3 different baseplate designs and their influence on the torque-compression relationship. Methods Three different RSA baseplate designs were evaluated through biomechanical testing using a glenoid vault, bone surrogate model. A digital torque gauge was used to measure insertion torque applied to the baseplate, whereas compression data were collected continuously from a load cell. Additionally, 2 predictive models were developed to predict the compression forces of each baseplate design at varying levels of torque. Results A linear relationship was found between baseplate compression and insertion torque for all 3 baseplate designs. Both the monoblock and 2-piece locking designs achieved the goal torque of 6.8 Nm, whereas the 2-piece nonlocking design did not due to material strip-out. No significant difference in maximum compression was found between the monoblock and 2-piece locking designs. However, the 2-piece nonlocking design achieved significantly higher compression. Both predictive models were shown to adequately predict compressive forces at different torque inputs for the monoblock and 2-piece locking designs but not the 2-piece nonlocking design. Conclusion The torque-compression relationship of a central screw baseplate is significantly affected by baseplate design. A 2-piece nonlocking baseplate reaches higher compression levels and risks material strip-out at lower insertional torques compared with a monoblock and 2-piece locking design. This has implications both on component design and on surgeon tactile feedback during surgery.
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Relationship Between Insertion Torque and Compression Strength in the Reverse Total Shoulder Arthroplasty Baseplate.
Journal of Orthopaedic Research, 2019Co-Authors: Miguel Diaz, Eric T Ricchetti, Grant E Garrigues, Sergio Gutierrez, Mark A FrankleAbstract:Reverse shoulder arthroplasty is a well-established procedure, however, there is limited data in the literature regarding adequate insertion torque and the resulting compression for glenoid baseplate fixation. In this biomechanical study, we evaluated the relationship between insertion torque and baseplate compression by simultaneously measuring the insertion torque and axial compressive forces generated by two reverse shoulder arthroplasty Baseplates with central screw design. Three different bone surrogates were chosen to mimic clinical scenarios where differences in compression achieved during baseplate insertion may exist due to varying bone quality. Epoxy resin sheets were combined with the bone surrogates to simulate the glenoid vault. A digital torque gauge was used to measure insertion torque applied to the baseplate, while compression data were collected continuously from a load cell. A strong positive correlation was found between baseplate compression and insertion torque. Among the lower density bone surrogates, neither baseplate design reached maximum insertion torque (6.8 Nm) due to material strip-out. This phenomenon did not occur in denser bone surrogates. Both baseplate designs experienced a significant increase in mean baseplate compression as insertion torque increased and were found to behave similar in the denser bone surrogates. The results presented here suggest that larger compressive forces can be achieved with an increase in insertion torque in denser bone surrogates, but caution must be used when trying to achieve fixation in poor-quality bone. Clinically, this could be useful preoperatively to minimize baseplate failure, and in further studies regarding baseplate design for improved initial fixation and stability. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:871-879, 2020.
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effects of tilt and glenosphere eccentricity on baseplate bone interface forces in a computational model validated by a mechanical model of reverse shoulder arthroplasty
Journal of Shoulder and Elbow Surgery, 2011Co-Authors: Sergio Gutierrez, Matthew Walker, Matthew Willis, Derek Pupello, Mark A FrankleAbstract:Hypothesis/background Reverse shoulder arthroplasty is being used with greater frequency for patients with severe rotator cuff deficiency. There are several commercially available reverse shoulder devices, each with different glenosphere options. The purpose of this study was to determine: (1) forces at the baseplate-bone interface in glenospheres with centers of rotation located concentrically and eccentrically to the center of the baseplate; and (2) if baseplate-bone forces can be optimized by altering tilt of the baseplate. Methods A validated computer model was used to compare concentric glenospheres with neutral offset to eccentrically offset glenospheres (6 mm inferior or 6 mm lateral) in 3 baseplate tilts: 15° inferior, neutral, or 15° superior. A baseplate, simulated bone, screws, and humeral component were modeled, and forces underneath the baseplate were calculated as the arm was abducted through 90° of glenohumeral motion. Results For lateral and concentric glenospheres, inferior tilt provides the most even distribution of forces (mean difference in force between superior and inferior portions of baseplate: 11.3 N and 24.7 N, respectively) and superior tilt provides the most uneven distribution of forces (109.3 N and 78.7 N, respectively). For inferior eccentric glenospheres, inferior tilt provides the most uneven distribution of forces (58.7 N) and neutral tilt provides the most even distribution of forces (27.7 N). Conclusion This is the first study to investigate force distribution under the baseplate in inferior eccentric glenospheres. Although inferior tilting of the baseplate is recommended for concentric and laterally offset glenospheres, this same recommendation may be detrimental to inferiorly offset glenospheres and warrants further investigation.
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Revision reverse shoulder arthroplasty for glenoid baseplate failure after primary reverse shoulder arthroplasty.
Journal of Shoulder and Elbow Surgery, 2009Co-Authors: Jason O. Holcomb, Derek Pupello, Derek J. Cuff, Steve A. Petersen, Mark A FrankleAbstract:Background The aim of this study is to document a single surgeon's experience performing revision reverse shoulder arthroplasty after baseplate failure. Methods Revision reverse shoulder arthroplasty (RSA) for mechanical failure of the glenoid baseplate after RSA was performed in 14 patients. Clinical and radiographic data were collected preoperatively, prior to baseplate failure, after baseplate failure, and at latest follow-up after revision (average, 33 months). Results When comparing the pre-operative values to post-revision, ASES, forward elevation, and abduction were significantly improved. There was no significant difference in any of the outcome measures when comparing the prefailure data to the post-revision data. The post-revision prosthesis-scapular neck angle (PSNA) showed a significant increase in inferior tilt of the baseplate when compared to pre-failure PSNA (P Conclusion Revision RSA for the treatment of glenoid baseplate mechanical failure can restore pain relief and function to the levels gained after the index RSA. Level of evidence Level IV, Case Series, Treatment Study.
David Veesler - One of the best experts on this subject based on the ideXlab platform.
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Structure of the type VI secretion system TssK–TssF–TssG baseplate subcomplex revealed by cryo-electron microscopy
Nature Communications, 2018Co-Authors: Young-jun Park, Christian Cambillau, Kaitlyn D. Lacourse, Frank Dimaio, Joseph D. Mougous, David VeeslerAbstract:Type VI secretion systems (T6SSs) translocate effectors into target cells and are made of a contractile sheath and a tube docked onto a multi-protein transmembrane complex via a baseplate. Although some information is available about the mechanisms of tail contraction leading to effector delivery, the detailed architecture and function of the baseplate remain unknown. Here, we report the 3.7 Å resolution cryo-electron microscopy reconstruction of an enteroaggregative Escherichia coli baseplate subcomplex assembled from TssK, TssF and TssG. The structure reveals two TssK trimers interact with a locally pseudo-3-fold symmetrical complex comprising two copies of TssF and one copy of TssG. TssF and TssG are structurally related to each other and to components of the phage T4 baseplate and of the type IV secretion system, strengthening the evolutionary relationships among these macromolecular machines. These results, together with bacterial two-hybrid assays, provide a structural framework to understand the T6SS baseplate architecture. Type VI secretion systems (T6SSs) translocate effector proteins into eukaryotic and bacterial recipient cells and are present in many Gram-negative bacteria. Here the authors present the 3.7 Å cryoEM structure of the E.coli T6SS baseplate wedge comprising TssK–TssF–TssG and propose a model for the T6SS baseplate and needle complex.
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Unraveling Lactococcal Phage Baseplate Assembly by Mass Spectrometry
Molecular & Cellular Proteomics, 2011Co-Authors: Dale A. Shepherd, Julie Lichiere, David Veesler, Alison E. Ashcroft, Christian CambillauAbstract:Bacteriophages belonging to the Caudovirales order possess a tail acting as a molecular machine used during infection to recognize the host and ensure high-efficiency genome delivery to the cell cytoplasm. They bear a large and sophisticated multiprotein organelle at their distal tail end, either a baseplate or a tail-tip, which is the control center for infectivity. We report here insights into the baseplate assembly pathways of two lactoccocal phages (p2 and TP901–1) using electrospray ionization-mass spectrometry. Based on our “block cloning” strategy we have expressed large complexes of their Baseplates as well as several significant structural subcomplexes. Previous biophysical characterization using size-exclusion chromatography coupled with on-line light scattering and refractometry demonstrated that the overproduced recombinant proteins interact with each other to form large (up to 1.9 MDa) and stable assemblies. The structures of several of these complexes have been determined by x-ray diffraction or by electron microscopy. In this contribution, we demonstrate that electrospray ionization-mass spectrometry yields accurate mass measurements for the different baseplate complexes studied from which their stoichiometries can be discerned, and that the subspecies observed in the spectra provide valuable information on the assembly mechanisms of these large organelles.
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solution and electron microscopy characterization of lactococcal phage Baseplates expressed in escherichia coli
Journal of Structural Biology, 2010Co-Authors: Valerie Campanacci, David Veesler, Julie Lichiere, Stephanie Blangy, Giuliano Sciara, Sylvain Moineau, Douwe Van Sinderen, Patrick Bron, Christian CambillauAbstract:Abstract We report here the characterization of several large structural protein complexes forming the Baseplates (or part of them) of Siphoviridae phages infecting Lactococcus lactis: TP901-1, Tuc2009 and p2. We revisited a “block cloning” expression strategy and extended this approach to genomic fragments encoding proteins whose interacting partners have not yet been clearly identified. Biophysical characterization of some of these complexes using circular dichroism and size exclusion chromatography, coupled with on-line light scattering and refractometry, demonstrated that the over-produced recombinant proteins interact with each other to form large (up to 1.9 MDa) and stable baseplate assemblies. Some of these complexes were characterized by electron microscopy confirming their structural homogeneity as well as providing a picture of their overall molecular shapes and symmetry. Finally, using these results, we were able to highlight similarities and differences with the well characterized much larger baseplate of the myophage T4.
Rémi Fronzes - One of the best experts on this subject based on the ideXlab platform.
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Biogenesis and structure of a type VI secretion baseplate
Nature Microbiology, 2018Co-Authors: Yassine Cherrak, Chiara Rapisarda, Riccardo Pellarin, Guillaume Bouvier, Benjamin Bardiaux, Fabrice Allain, Christian Malosse, Julia Chamot-rooke, Eric Cascales, Rémi FronzesAbstract:To support their growth in a competitive environment and cause pathogenesis, bacteria have evolved a broad repertoire of macromolecular machineries to deliver specific effectors and toxins. Among these multiprotein complexes, the type VI secretion system (T6SS) is a contractile nanomachine that targets both prokaryotic and eukaryotic cells. The T6SS comprises two functional subcomplexes: a bacteriophage-related tail structure anchored to the cell envelope by a membrane complex. As in other contractile injection systems, the tail is composed of an inner tube wrapped by a sheath and built on the baseplate. In the T6SS, the baseplate is not only the tail assembly platform, but also docks the tail to the membrane complex and hence serves as an evolutionary adaptor. Here we define the biogenesis pathway and report the cryo-electron microscopy (cryo-EM) structure of the wedge protein complex of the T6SS from enteroaggregative Escherichia coli (EAEC). Using an integrative approach, we unveil the molecular architecture of the whole T6SS baseplate and its interaction with the tail sheath, offering detailed insights into its biogenesis and function. We discuss architectural and mechanistic similarities but also reveal key differences with the T4 phage and Mu phage Baseplates. The cryo-EM structure of the TssKFGE baseplate wedge complex of the type VI secretion system (T6SS) from enteroaggregative Escherichia coli helps to elucidate the molecular architecture of the whole T6SS baseplate, and its assembly and mode of action.
