Structural Fundamentals of Gliding Motility
Lead Research Organisation:
University of Birmingham
Department Name: Sch of Biosciences
Abstract
Movement has a huge role to play in all aspects of cellular life: escape from harm, colonizing hosts in disease, moving towards a food source - anything where an advantage can be gained by changing environment. Currently there is a bias in what we know about the different modes of cellular motility, for example we have an excellent molecular understanding of swimming (via a rotary "tail"-like apparatus called the flagellum) and slingshot crawling (via a grappling hook like apparatus called the type 4 pilus). Conversely, we know very little about how bacterial gliding works, a means of motility where the cell slides on a surface with no visible clues as to how propulsion is achieved.
We do however know the genes involved, and these are often present in predatory bacteria, specialized organisms that use gliding to hunt and kill their fellow bacteria. One of these predators, Bdellovibrio (our organism of choice for this study) may even prove useful in killing the antibiotic resistant bacteria that are an emerging problem in healthcare. An improved understanding of gliding would lead us to understand predators better, particularly in terms of how they navigate prey-rich surfaces known as biofilms. Besides healthcare, there may be applications for Bdellovibrio and related predators in crop pestilence, food safety, biofouling and water treatment.
Our investigation here aims to validate a model in which we have pieced together several identified gliding components (proteins) around a common hub that aims to organize these in conveying energy from inside the cell to a means of propulsion outside the cell. Excitingly, our preliminary studies provide intuitive roles for each of the pieces, and suggest that the adhesive part is related to a known system from human cells - hence there may be an evolutionary link where bacterial movement was the progenitor for other systems. This will be driven by structural and biochemical understanding of how the gliding proteins fit together and interact with one another, which should also involve several states/poses that ultimately tell us how the machinery works.
Results from our study will be "first-in-class", as nothing is currently known about the molecular details of the gliding machinery. The work will have broad impact - there will be key similarities and differences to other modes of movement that will enrich our understanding (as well as stimulating the direct field of predatory bacteria).
We do however know the genes involved, and these are often present in predatory bacteria, specialized organisms that use gliding to hunt and kill their fellow bacteria. One of these predators, Bdellovibrio (our organism of choice for this study) may even prove useful in killing the antibiotic resistant bacteria that are an emerging problem in healthcare. An improved understanding of gliding would lead us to understand predators better, particularly in terms of how they navigate prey-rich surfaces known as biofilms. Besides healthcare, there may be applications for Bdellovibrio and related predators in crop pestilence, food safety, biofouling and water treatment.
Our investigation here aims to validate a model in which we have pieced together several identified gliding components (proteins) around a common hub that aims to organize these in conveying energy from inside the cell to a means of propulsion outside the cell. Excitingly, our preliminary studies provide intuitive roles for each of the pieces, and suggest that the adhesive part is related to a known system from human cells - hence there may be an evolutionary link where bacterial movement was the progenitor for other systems. This will be driven by structural and biochemical understanding of how the gliding proteins fit together and interact with one another, which should also involve several states/poses that ultimately tell us how the machinery works.
Results from our study will be "first-in-class", as nothing is currently known about the molecular details of the gliding machinery. The work will have broad impact - there will be key similarities and differences to other modes of movement that will enrich our understanding (as well as stimulating the direct field of predatory bacteria).
Technical Summary
We will use the model predatory bacterium Bdellovibrio, which encodes several copies of the minimal Glt machinery, to study gliding motility. Gliding is enigmatic, with the need to couple energy transduction across two membranes to selective surface adhesion, without this machinery adopting a state amenable to EM or tomography. Hence we will piece together the apparatus using x-ray crystallography to study defined complexes, and test interactions using protein biochemistry (pulldowns, ITC, MST).
Our preliminary data reveals that the ~1000aa major gliding machinery component GltD forms a TPR-rich structure suitable for interaction with the other GltABCEFG components. Co-evolutionary analysis suggests that GltD forms a link between outer-membrane elements (GltABCF) at its N-terminal end and distal elements at its C-terminal end (GltEG). We will investigate this hypothesis, particularly the compelling idea that this allows coupling between the Ton fold of GltG and a ton site in GltF (ultimately connecting the inner membrane proton pump to conformational change at the outer membrane).
We have further preliminary data on a set of gliding cluster metal-ion dependent adhesin lipoproteins, whose structure suggests functional homology to eukaryotic integrins. Integrins switch between two states, turning adhesion on and off. We will investigate whether/where these lipoproteins bind the GltABCDEFG gliding complex, and if we can obtain "on" and "off" states for them by using mutagenesis inspired by the integrin field. If associated with the outer membrane components, we anticipate being able to link this to signals from inside the cell, providing an intuitive answer to the problem of identifying a stick/slip mechanism for propulsion.
The summated aim of this research is to provide the first molecular details as to how the Glt proteins are arranged (this is unknown at any resolution, let alone at the atomic level), and how they functionally interact for gliding to occur.
Our preliminary data reveals that the ~1000aa major gliding machinery component GltD forms a TPR-rich structure suitable for interaction with the other GltABCEFG components. Co-evolutionary analysis suggests that GltD forms a link between outer-membrane elements (GltABCF) at its N-terminal end and distal elements at its C-terminal end (GltEG). We will investigate this hypothesis, particularly the compelling idea that this allows coupling between the Ton fold of GltG and a ton site in GltF (ultimately connecting the inner membrane proton pump to conformational change at the outer membrane).
We have further preliminary data on a set of gliding cluster metal-ion dependent adhesin lipoproteins, whose structure suggests functional homology to eukaryotic integrins. Integrins switch between two states, turning adhesion on and off. We will investigate whether/where these lipoproteins bind the GltABCDEFG gliding complex, and if we can obtain "on" and "off" states for them by using mutagenesis inspired by the integrin field. If associated with the outer membrane components, we anticipate being able to link this to signals from inside the cell, providing an intuitive answer to the problem of identifying a stick/slip mechanism for propulsion.
The summated aim of this research is to provide the first molecular details as to how the Glt proteins are arranged (this is unknown at any resolution, let alone at the atomic level), and how they functionally interact for gliding to occur.
Organisations
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ORCID iD |
| Andrew Lovering (Principal Investigator) |