FIG 6.

VolA requires a catalytic serine within a conserved lipase motif for activity. (A) Alignment of the protein region containing the conserved lipase motif Gly-Xaa-Ser-Xaa-Gly (residues 549 to 553 in V. cholerae VolA). Homologs of VolA were identified in Vibrio species and other marine organisms. (B) Anti-VolA Western blot of cell lysate expressing wild-type VolA or one of the VolA mutants (S551A and S551T). Mutant proteins were strongly expressed despite mutation of the active-site serine. (C) Growth of the V. cholerae volA mutant expressing either wild-type VolA or VolA catalytic serine mutants on LPC as the sole carbon source. Both S551A and S551T mutants failed to grow using LPC. (D) Lysophospholipase assay of membranes expressing either wild-type VolA or VolA S551 or S551T mutants.