Molecular Characterization of EspB: A Phospholipid Binding Mycobacterium tuberculosis Virulence Factor
Chung, Beatrice *,1, 2; Chen, Jeffrey 1, 2
1. Vaccine and Infectious Disease Organization – International Vaccine Centre (VIDO-InterVac) University of Saskatchewan, Saskatoon, Canada
2. Department of Biochemistry, Microbiology and Immunology, University of Saskatchewan, Saskatoon, Canada
Mycobacterium tuberculosis (M. tb) uses its type-7 ESX-1 secretion system to translocate protein virulence effectors to subvert the host immune response during infection. One of the proteins secreted through this system is EspB, which was previously found to have a distinct virulence function that may be dependent on phospholipid binding. In this study, we sought to determine the molecular basis of EspB-phospholipid interactions, by replacing amino acid residues predicted to be critical for phospholipid binding (EspBR17A/H223A, EspBF159R/I246R). Moreover, as structural studies have determined that secreted EspB forms heptamers, we also replaced amino acid residues predicted to be critical for oligomerization (EspBW176R, EspBK259A/K267A). These recombinant variants were produced in E. coli and assessed for phospholipid binding as well as oligomerization behaviour. We show that the amino acid residues R17 and H223 of EspB are important for phospholipid binding. However, oligomerization of EspB does not appear to be critical for phospholipid binding. Finally, we provide strong evidence that suggests EspB-mediated virulence is indeed dependent on phospholipid binding.