title: Rv1698 of Mycobacterium tuberculosis represents a new class of channel-forming outer membrane proteins.
abstract: 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. Only OmpA, which has numerous homologs in Gram-negative bacteria, is known to form channels in the outer membrane of M. tuberculosis so far. Rv1698 was predicted to be an outer membrane protein of unknown function. Expression of rv1698 restored the sensitivity to ampicillin and chloramphenicol of a Mycobacterium smegmatis mutant lacking the main porin MspA. Uptake experiments showed that Rv1698 partially complemented the permeability defect of the M. smegmatis porin mutant for glucose. These results indicated that Rv1698 provides an unspecific pore that can partially substitute for MspA. Lipid bilayer experiments demonstrated that purified Rv1698 is an integral membrane protein that indeed produces channels. The main single channel conductance is 4.5 +/- 0.3 nanosiemens in 1 M KCl. Zero current potential measurements revealed a weak preference for cations. Whole cell digestion of recombinant M. smegmatis with proteinase K showed that Rv1698 is surface-accessible. Taken together, these experiments demonstrated that Rv1698 is a channel protein that is likely involved in transport processes across the outer membrane of M. tuberculosis. Rv1698 has single homologs of unknown functions in Corynebacterineae and thus represents the first member of a new class of channel proteins specific for mycolic acid-containing outer membranes.
authors.affiliation: Department of Microbiology, University of Alabama at Birmingham, Birmingham, AL 35294, USA.
authors.forename: Axel
authors.initials: A
authors.lastname: Siroy
authors.forename: Claudia
authors.initials: C
authors.lastname: Mailaender
authors.forename: Daniel
authors.initials: D
authors.lastname: Harder
authors.forename: Stephanie
authors.initials: S
authors.lastname: Koerber
authors.forename: Frank
authors.initials: F
authors.lastname: Wolschendorf
authors.forename: Olga
authors.initials: O
authors.lastname: Danilchanka
authors.forename: Ying
authors.initials: Y
authors.lastname: Wang
authors.forename: Christian
authors.initials: C
authors.lastname: Heinz
authors.forename: Michael
authors.initials: M
authors.lastname: Niederweis
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry* / Q000145:classification; D002462:Cell Membrane / Q000378:metabolism*; D019286:Endopeptidase K / Q000737:chemistry; D004926:Escherichia coli / Q000378:metabolism; D005947:Glucose / Q000737:chemistry / Q000378:metabolism; D008051:Lipid Bilayers / Q000737:chemistry; D008954:Models, Biological; D009154:Mutation; D009163:Mycobacterium bovis / Q000378:metabolism; D020102:Mycobacterium smegmatis / Q000378:metabolism; D009169:Mycobacterium tuberculosis / Q000378:metabolism*; D017354:Point Mutation; D018272:Porins / Q000737:chemistry; D017433:Protein Structure, Secondary
chemical_list: D000900:Anti-Bacterial Agents; D001425:Bacterial Outer Membrane Proteins; D008051:Lipid Bilayers; D018272:Porins; D019286:Endopeptidase K; D005947:Glucose