1.B.50 The Acid-fast Bacterial, Outer Membrane Porin (AFB-OMP) Family
Mycobacteria contain an outer membrane composed of mycolic acids and a large variety of other lipids. Its protective function is an essential virulence factor of Mycobacterium tuberculosis. Rv1698 was predicted to be an outer membrane protein. Expression of rv1698 restored the sensitivity to ampicillin and chloramphenicol of a mutant of Mycobacterium smegmatis lacking the main porin MspA. Rv1698 complements the permeability defect of the M. smegmatis porin mutant for glucose and is surface-accessible (Siroy et al., 2008). Lipid bilayer experiments demonstrated that purified Rv1698 is an integral membrane protein which produces channels. The main conductance is 4.5 /- 0.3 nS in 1 M KCl with weak preference for cations. Thus, Rv1698 is a channel protein that is likely involved in transport processes across the outer membrane of M. tuberculosis. Rv1698 has single homologs in Corynebacterineae and is the first characterized member of a new class of channel proteins specific for mycolic acid-containing outer membranes.
Homologues are present in other low and high G C Gram-positive bacteria, Gram-negative bacteria, and Archaea with outer mycolic acid-containing membranes. Rv1698 is distantly related to 9.A.42.1.1 (O53943).