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Michael G. Rossmann – One of the best experts on this subject based on the ideXlab platform.

  • Structure of the 3.3 MDa, in vitro assembled, hubless bacteriophage T4 baseplate
    Journal of Structural Biology, 2014
    Co-Authors: Thomas Klose, Fumio Arisaka, Anastasia A. Aksyuk, Pavel Plevka, Xinzheng Zhang, Michael G. Rossmann

    Abstract:

    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.

  • Structure and function of bacteriophage T4
    Future Microbiology, 2014
    Co-Authors: Moh Lan Yap, Michael G. Rossmann

    Abstract:

    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.

  • The Structure of Gene Product 6 of Bacteriophage T4, the Hinge-Pin of the Baseplate
    Structure, 2009
    Co-Authors: Anastasia A. Aksyuk, Vadim V. Mesyanzhinov, Petr G. Leiman, Mikhail M. Shneider, Michael G. Rossmann

    Abstract:

    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.

Christian Cambillau – One of the best experts on this subject based on the ideXlab platform.

  • Structural Insights into Lactococcal Siphophage p2 Baseplate Activation Mechanism
    Viruses, 2020
    Co-Authors: Silvia Spinelli, Christian Cambillau, Sylvain Moineau, Denise M. Tremblay, Adeline Goulet

    Abstract:

    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.

  • Structure of the type VI secretion system TssK–TssF–TssG baseplate subcomplex revealed by cryo-electron microscopy
    Nature Communications, 2018
    Co-Authors: Young-jun Park, Christian Cambillau, Kaitlyn D. Lacourse, Frank Dimaio, Joseph D. Mougous, David Veesler

    Abstract:

    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.

  • Bacteriophage module reshuffling results in adaptive host range as exemplified by the baseplate model of listerial phage A118.
    Virology, 2015
    Co-Authors: Christian Cambillau

    Abstract:

    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.

Mark A Frankle – One of the best experts on this subject based on the ideXlab platform.

  • Influence of reverse total shoulder arthroplasty baseplate design on torque and compression relationship.
    JSES international, 2020
    Co-Authors: Miguel A Diaz, Sergio Gutierrez, Eric T Ricchetti, Grant E Garrigues, Mark A Frankle

    Abstract:

    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.

  • Influence of reverse total shoulder arthroplasty baseplate design on torque and compression relationship
    , 2020
    Co-Authors: Miguel A Diaz, Sergio Gutierrez, Eric T Ricchetti, Grant E Garrigues, Mark A Frankle

    Abstract:

    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.

  • Relationship Between Insertion Torque and Compression Strength in the Reverse Total Shoulder Arthroplasty Baseplate.
    Journal of Orthopaedic Research, 2019
    Co-Authors: Miguel Diaz, Eric T Ricchetti, Sergio Gutierrez, Grant E Garrigues, Mark A Frankle

    Abstract:

    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.