Structure Of The Mycobacterium Tuberculosis Virulence Factor Rv0899 (Ompatb)

Rv0899 (OmpATb) is a 326-residue membrane-associated virulence factor of Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis. It is essential for the adaptation of Mtb to acidic environments and has been identified as an outer membrane protein. The M domain (residues 1-72) contains a 20-residue hydrophobic sequence that may form a membrane-anchoring helix. The B domain (residues 73-195) has been described as pore-forming. It shares sequence homology with the “BON” domain of Bacterial Osmotic-shock-resistance, Nodulation-specificity and lipid-binding proteins. The C domain (residue 196-326) shares significance homology with other bacterial peptidoglycan-binding domains, including the C-terminus of the E. coli outer membrane protein OmpA, after which Rv0899 was originally named. Using NMR spectroscopy, we show that residues 73-326, spanning the joint B and C domains, adopt a well-defined three-dimensional structure in water solution, however, the individual B and C domains fold independently and interact with each other to a minimal extent. The B domain adopts a rigid and stable structure, that forms a six-stranded β-sheet protected on one side by three α-helices. No comparable arrangement of secondary structure elements could be found in the databases, suggesting that is a new fold. The structure of the B domain is suggestive of a lipid binding or structural function, and provides insights to the role of Rv0899 in Mtb virulence. (This research was supported by the National Institutes of Health (NIH), and utilized the Burnham Institute NMR Facility supported by the NIH National Cancer Institute).