Biology subjects

Troman, L.

Publications and source records attributed to Troman, L..

4 recordsLinked to original sources

bioRxiv2026

Structural basis for curvature generation and functional specialization in spirochete flagella

Spirochetes are a distinctive phylum of spiral-shaped bacteria, defined by their curved periplasmic flagella, which drive motility by deforming the cell body and enabling efficient corkscrew-like propulsion through viscous environments. Despite their clinical importance, the molecular mechanisms underlying flagellar assembly, curvature and thus motility, remain poorly understood. Here we used cryo-electron microscopy combined with visual proteomic analysis to determine near-atomic resolution structures of two distinct flagellar filaments natively isolated from T. denticola, a major oral pathogen. Our structures reveal that filament curvature is generated by the asymmetric decoration of a conserved FlaB core by multiple sheath proteins, including FlaA1/2/3 and two previously uncharacterized proteins, termed FlaL1 and FlaL2. We show that the sheath imposes differential axial compaction on the FlaB core: FlaA1 expands the lattice at the outer curvature, FlaA2/3 compress the lattice at the inner curvature, and FlaL proteins stabilize these asymmetric interactions. Incorporation of distinct FlaB homologs contributes to assembled filament identity, with FlaB3 forming thin filaments and FlaB1/2 interacting with the sheath to form thick filaments. Comparative analysis reveals that FlaL proteins are conserved amongst some Treponema species and several other spirochetes, indicating that asymmetric assembly represents a modular solution to the mechanical demands of periplasmic flagella. These findings provide a structural framework for understanding functional specialization in bacterial filaments.

microbiology↗

bioRxiv2024

Mechanistic basis of temperature-adaptation in microtubule dynamics across frog species

Cellular processes are remarkably effective across diverse temperature ranges, even with highly conserved proteins. In the context of the microtubule cytoskeleton, which is critically involved in a wide range of cellular activities, this is particularly striking as tubulin is one of the most conserved proteins while microtubule dynamic instability is highly temperature sensitive. We thus lack a mechanistic framework that links functional adaptability with environmental pressures. Here, we leverage the diversity of natural tubulin variants from three closely related frog species that live at different temperatures: we combine in vitro reconstitution assays, quantitative biochemistry, and cryogenic electron microscopy to show how a small number of primary sequence changes influences the energy landscape of tubulin interactions and thereby mediates cold-adaptation and microtubule stability. This study thus broadens our conceptual framework for understanding microtubule dynamics and provides insights into how conserved cellular processes are tailored to different ecological niches.

biochemistry↗

bioRxiv2022

INTERACTION OF THE PERIPLASMIC CHAPERONE SURA WITH THE INNER MEMBRANE PROTEIN SECRETION (SEC) MACHINERY

Gram-negative bacteria are surrounded by two protein-rich membranes with a peptidoglycan layer sandwiched between them. Together they form the envelope (or cell wall), crucial for energy production, lipid biosynthesis, structural integrity, and for protection against the physical and chemical environmental challenges. To achieve envelope biogenesis, periplasmic and outer-membrane proteins (OMPs) must be transported from the cytosol and through the inner-membrane, via the ubiquitous SecYEG protein-channel. Emergent proteins either fold in the periplasm or cross the peptidoglycan (PG) layer towards the outer-membrane for insertion through the {beta}-barrel assembly machinery (BAM). Trafficking of hydrophobic proteins through the periplasm is particularly treacherous given the high protein density and the absence of energy (ATP or chemiosmotic potential). Numerous molecular chaperones assist in the prevention and recovery from aggregation, and of these SurA is known to interact with BAM, facilitating delivery to the outer-membrane. However, it is unclear how proteins emerging from the Sec-machinery are received and protected from aggregation and proteolysis prior to an interaction with SurA. Through biochemical analysis and electron microscopy we demonstrate the binding capabilities of the unoccupied and substrate-engaged SurA to the inner-membrane translocation machinery complex of SecYEG-SecDF-YidC - aka the holo-translocon (HTL). Supported by AlphaFold predictions, we suggest a role for periplasmic domains of SecDF in chaperone recruitment to the protein translocation exit site in SecYEG. We propose that this immediate interaction with a recruited chaperone helps to prevent aggregation and degradation of nascent envelope proteins, facilitating their safe passage to the periplasm and outer-membrane.

biochemistry↗

bioRxiv2019

Trans-membrane association of the Sec and BAM complexes for bacterial outer-membrane biogenesis

SUMMARYThe outer-membrane of Gram-negative bacteria is critical for surface adhesion, pathogenicity, antibiotic resistance and survival. The major constituent – hydrophobic β-barrel Outer-Membrane Proteins (OMPs) – are secreted across the inner-membrane through the Sec-translocon for delivery to periplasmic chaperones e.g. SurA, which prevent aggregation. OMPs are then offloaded to the β-Barrel Assembly Machinery (BAM) in the outer-membrane for insertion and folding. We show the Holo-TransLocon (HTL: an assembly of the protein-channel core-complex SecYEG, the ancillary sub-complex SecDF, and the membrane ‘insertase’ YidC) contacts SurA and BAM through periplasmic domains of SecDF and YidC, ensuring efficient OMP maturation. Our results show the trans-membrane proton-motive-force (PMF) acts at distinct stages of protein secretion: for SecA-driven translocation across the inner-membrane through SecYEG; and to communicate conformational changes via SecDF to the BAM machinery. The latter presumably ensures efficient passage of OMPs. These interactions provide insights of inter-membrane organisation, the importance of which is becoming increasingly apparent.Competing Interest StatementThe authors have declared no competing interest.View Full Text

biochemistry↗