Biology subjects

Borsch, M.

Publications and source records attributed to Borsch, M..

2 recordsLinked to original sources

bioRxiv2024

Lymphostatin: Structure of a large multi-functional virulence factor

Enteropathogenic and Enterohaemorrhagic Escherichia coli are enteric pathogens of global importance and human infections can be life-threatening. Lymphostatin is a key virulence factor of these bacteria, being required for intestinal colonisation and a potent inhibitor of the mitogen- and antigen-activated proliferation of lymphocytes and proinflammatory responses. In some strains, it also mediates adherence to host cells and influences actin nucleation at sites of attachment. This 365 kDa protein requires glycosyltransferase and cysteine protease motifs for activity against lymphocytes, but high-resolution structural information has proven elusive and the molecular mechanisms by which it acts remain unclear. Here, we describe the structure of lymphostatin from the prototype O127:H6 enteropathogenic E. coli strain determined by electron cryo-microscopy. Our results reveal two glycosyltransferase domains, one PaTox-like protease domain, an ADP-ribosyltransferase domain, and a delivery domain. Long linkers act to hold these domains together. These linkers occlude the catalytic sites of the N-terminal glycosyltransferase and protease domains. In this dormant state, lymphostatin binds to HEK-293T cells, where it forms large clusters before being taken up and sequestered into cytosolic foci. With more functional domains than any other known large bacterial toxin, lymphostatin can be regarded as the multifunctional Swiss army knife of pathogenic Escherichia coli, enabling complex interactions with the host cells in different environments.

biophysics↗

bioRxiv2023

Mechanism of ADP-inhibited ATP hydrolysis in single proton-pumping FoF1-ATP synthase trapped in solution

FoF1-ATP synthases in mitochondria, in chloroplasts and in most bacteria are the proton-driven membrane enzymes supplying the cells with ATP made from ADP and phosphate. To monitor and prevent the reverse chemical reaction of fast wasteful ATP hydrolysis by the enzymes, different control mechanisms exist including mechanical or redox-based blockade of catalysis and ADP inhibition. In general product inhibition is expected to slow down the mean catalytic turnover. However, biochemical assays are ensemble measurements and cannot discriminate between a mechanism affecting all enzymes equally or individually. For example, all enzymes could work slower at a decreasing substrate/product ratio, or more and more individual enzymes are blocked completely. Here, we examined how increasing amounts of ADP affected ATP hydrolysis of single Escherichia coli FoF1-ATP synthases in liposomes. We observed individual catalytic turnover of the enzymes one after another by monitoring the internal subunit rotation using single-molecule Forster resonance energy transfer (smFRET). Observation times of single FRET-labeled FoF1-ATP synthase in solution were increased up to seconds using a confocal Anti-Brownian electrokinetic trap (ABEL trap). By counting active versus inhibited enzymes we revealed that ADP inhibition did not decrease the catalytic turnover of all FoF1-ATP synthases equally. Instead, increasing ADP in the ADP/ATP mixture reduced the number of the remaining active enzymes which were operating at similar catalytic rates for varying substrate/product ratios.

biophysics↗