Biology subjects

Eastep, G. N.

Publications and source records attributed to Eastep, G. N..

3 recordsLinked to original sources

bioRxiv2025

Distinct flagellins differentially fine tune biofilm initiation via flagellar stator-associated proteins

Helicobacter pylori relies on flagellar motility to colonize the gastric niche. While H. pylori flagella serve multiple functions, including swimming motility, it has recently been appreciated that flagellar basal body properties also contribute to biofilm initiation. The H. pylori flagellar filament contains two spatially segregated flagellins, FlaA and FlaB, but their roles in the biofilm initiation process remained undefined. Here, we confirmed that both FlaA and FlaB are required for optimal motility, but found that they exert opposite effects on biofilm initiation: cells without FlaA display low biofilm initiation, while cells without FlaB display elevated initiation. To understand the molecular basis for this divergence, cryo-electron microscopy (cryo-EM) analysis of native flagellar filaments revealed that FlaA and FlaB have distinct supercoiled waveforms. We confirmed these intrinsic waveform curvatures by analyzing filaments from {Delta}flaA and {Delta}flaB mutants, providing a physical basis for their functional specialization. Genetic epistasis experiments further demonstrated that the enhanced early biofilm formation of the {Delta}flaB mutant depends on PilO, a stator-associated component of the flagellar motor recently shown to drive a reciprocal biofilm and motility response. Our findings establish that H. pylori has developed functionally specialized flagellins that work with motor-dependent signaling to dynamically balance surface colonization and motility.

microbiology↗

bioRxiv2023

Two dramatically distinct archaeal type IV pili structures formed by the same pilin

Type IV pili (T4P) represent one of the most common varieties of surface appendages in archaea. These filaments, assembled from relatively small pilin proteins, can be many microns long and serve diverse functions, including adhesion, biofilm formation, motility, and intercellular communication. Using cryo-electron microscopy (cryo-EM), we determined atomic structures of two dramatically different T4P from Saccharolobus islandicus REY15A. Unexpectedly, both pili were assembled from the same pilin protein but under different growth conditions. One filament, denoted mono-pilus, conforms to canonical archaeal T4P structures where all subunits are equivalent, whereas in the other filament, the tri-pilus, the same protein exists in three different conformations. The three conformations involve different orientations of the outer immunoglobulin (Ig)-like domains, mediated by a very flexible linker, and all three of these conformations are very different from the single conformation found in the mono-pilus. Remarkably, the outer domains rotate nearly 180{degrees} between the mono- and tri-pilus conformations, formally similar to what has been shown for outer domains in bacterial flagellar filaments, despite lack of homology between bacterial flagella and archaeal T4P. Interestingly, both forms of pili require the same ATPase and TadC-like membrane pore for assembly, indicating that the same secretion system can produce structurally very different filaments. However, the expression of the ATPase and TadC genes was significantly different under the conditions yielding mono- and tri-pili. While archaeal T4P are homologs of archaeal flagellar filaments, our results show that in contrast to the rigid supercoil that the flagellar filaments must adopt to serve as helical propellers, archaeal T4P are likely to have fewer constraints on their structure and enjoy more internal degrees of freedom.

microbiology↗

bioRxiv2020

Structural characterization of HIV-1 matrix mutants implicated in envelope incorporation

During the late phase of HIV-1 infection, viral Gag polyproteins are targeted to the plasma membrane (PM) for assembly. Gag localization at the PM is a prerequisite for the incorporation of the envelope protein (Env) into budding particles. Gag assembly and Env incorporation are mediated by the N-terminal myristoylated matrix (MA) domain of Gag. Nonconservative mutations in the trimer interface of MA (A45E, T70R, and L75G) were found to impair Env incorporation and infectivity, leading to the hypothesis that MA trimerization is an obligatory step for Env incorporation. Conversely, Env incorporation can be rescued by a compensatory mutation in the MA trimer interface (Q63R). The impact of these MA mutations on the structure and trimerization properties of MA is not known. In this study, we employed NMR spectroscopy, x-ray crystallography, and sedimentation techniques to characterize the structure and trimerization properties of HIV-1 MA A45E, Q63R, T70R, and L75G mutant proteins. NMR data revealed that these point mutations did not alter the overall structure and folding of MA but caused minor structural perturbations in the trimer interface. Analytical ultracentrifugation data indicated that mutations had a minimal effect on the MA monomer-trimer equilibrium. The high-resolution x-ray structure of the unmyristoylated MA Q63R protein revealed hydrogen bonding between the side chains of Arg-63 and Ser-67 located in the center of the trimer interface, providing the first structural evidence for a stabilization of the trimer form. These findings advance our knowledge of the interplay of MA trimerization and Env incorporation into HIV-1 particles.

biochemistry↗