Biology subjects

McCausland, J.

Publications and source records attributed to McCausland, J..

4 recordsLinked to original sources

bioRxiv2026

A cofactor-promiscuous HMGR from the Lyme disease pathogen illuminates diversity in bacterial isoprenoid biosynthesis

The Lyme disease pathogen Borrelia burgdorferi contains a highly reduced genome lacking many primary metabolic pathways. However, B. burgdorferi retains the mevalonate pathway that synthesizes isopentenyl pyrophosphate (IPP), the precursor to the peptidoglycan carrier lipid. While the mevalonate pathway and the enzyme that catalyzes its rate-limiting step (3-hydroxy-3-methyl glutaryl coenzyme A reductase, HMGR) are well studied in vertebrates, little is known about the pathway in B. burgdorferi and many pathogenic bacteria. In this work, we reveal that HMGR is a critical metabolic enzyme in B. burgdorferi. We demonstrate that loss of HMGR causes morphological defects and muted de novo synthesis of peptidoglycan; these defects are ameliorated by exogenous mevalonate and IPP. Biochemical characterization unveiled the HMGR as a highly unusual cofactor-promiscuous oxidoreductase that functions with both nicotinamide cofactors. Bioinformatics and biochemical characterization uncovered examples of similarly promiscuous HMGRs and revealed a previously unrecognized evolutionary link to cofactor choice. Moreover, structures of the enzyme reveal a highly divergent active site architecture. Together, these findings firmly establish HMGR as an opportunity target for the development of antibacterials for a diderm pathogen while highlighting cofactor promiscuity as an evolutionary acquired feature in HMGRs.

biochemistry↗

bioRxiv2026

The Unexpected Visibility of the SARS-CoV-2 Nucleocapsid Protein Reveals a Hidden Route of Surface Trafficking.

The SARS-CoV-2 Nucleocapsid (N) protein, long regarded as an internal structural component of the virion, unexpectedly localizes to the plasma membrane of infected cells. Here, we show that N is actively trafficked to the cell surface via a ceramide-dependent unconventional secretory pathway. Live-stained imaging and kinetic analyses revealed that N surface association begins early in infection, before Spike (S) expression and viral release, and persists after enzymatic removal of heparan sulfate. Pharmacological disruption of phosphoinositide or phosphatidylserine interactions had minimal effect, whereas inhibition of neutral sphingomyelinase with GW4869 markedly reduced surface N, identifying a ceramide-regulated route as essential for its export. This mechanism distinguishes N from canonical transmembrane viral proteins and explains how N-specific antibodies mediate potent Fc-effector responses across SARS-CoV-2 variants. Our findings redefine the spatiotemporal dynamics of coronavirus structural proteins and reveal an unanticipated axis of immune visibility within the infected cell. IMPORTANCEInternal viral proteins are generally thought to remain confined to intracellular compartments, yet several viruses display such proteins at the surface of infected cells through mechanisms that remain incompletely defined. In this study, we characterize a host-regulated trafficking route that contributes to the delivery of the SARS-CoV-2 nucleocapsid (N) protein, a non-membrane viral protein, to the plasma membrane. Our findings indicate that N protein surface expression occurs independently of virion assembly, membrane integration, or extracellular rebinding, and instead involves host vesicular processes outside the classical secretory pathway. By elucidating how a leaderless coronavirus protein can access the cell surface, this work addresses a key gap in coronavirus cell biology and provides a framework for understanding how internal viral proteins may exploit host trafficking pathways. More broadly, these results highlight unconventional host trafficking pathways as determinants of viral protein localization and provide a framework for understanding how viruses exploit cellular export mechanisms beyond the classical secretory system.

cell biology↗

bioRxiv2022

Conformational changes in the essential E. coli septal cell wall synthesis complex suggest an activation mechanism

The bacterial divisome, a macromolecular machine that is composed of more than thirty proteins in E. coli, orchestrates the essential process of cell wall constriction during cell division. Novel antimicrobial strategies can target protein-protein interactions within the divisome and will benefit from insights into divisome structure and dynamics. In this work, we combined structure prediction, molecular dynamics simulation, single-molecule imaging, and mutagenesis to construct a model of the core complex of the E. coli divisome composed of the essential septal cell wall synthase complex formed by FtsW and FtsI, and its regulators FtsQ, FtsL, FtsB, and FtsN. We observed extensive interactions in four key regions in the periplasmic domains of the complex. FtsQ, FtsL, and FtsB scaffold FtsI in an extended conformation with the FtsI transpeptidase domain lifted away from the membrane through interactions among the C-terminal domains. FtsN binds between FtsI and FtsL in a region rich in residues with superfission (activating) and dominant negative (inhibitory) mutations. Mutagenesis experiments in cellulo and in silico revealed that the essential domain of FtsN functions as a tether to tie FtsI and FtsL together, impacting interactions between the anchor-loop of FtsI and the putative catalytic region of FtsW, suggesting a mechanism of how FtsN activates the cell wall synthesis activities of FtsW and FtsI.

biophysics↗

bioRxiv2022

Light-dependent modulation of protein localization and function in living bacteria cells

Most bacteria lack membrane-enclosed organelles to compartmentalize cellular processes. In lieu of physical compartments, bacterial proteins are often recruited to macromolecular scaffolds at specific subcellular locations to carry out their functions. Consequently, the ability to modulate a proteins subcellular location with high precision and speed bears the potential to manipulate its corresponding cellular functions. Here we demonstrate that the CRY2/CIB1 system from Arabidopsis thaliana can be used to rapidly direct proteins to different subcellular locations inside live E. coli cells including the nucleoid, the cell pole, membrane, and the midcell division plane. We further show that such light-induced re-localization can be used to rapidly inhibit cytokinesis in actively dividing E. coli cells. Finally, we demonstrate that the CRY2/CIBN binding kinetics can be modulated by green light, adding a new dimension of control to the system.

synthetic biology↗