This is the extracellular domain (ECD) found in FtsX enzyme, a homolog of the transmembrane PG-hydrolase regulator. The FtsX extracellular domain binds the PG peptidase Rv2190c/RipC N-terminal segment, causing a conformational change that activates the enzyme ileading to PG hydrolysis in Mycobacterium tuberculosis. Structural analysis of FtsX ECD reveals fold containing two lobes connected by a flexible hinge. Mutations in the hydrophobic cleft between the lobes showed reduction in RipC binding in vitro and inhibition of FtsX function in Mycobacterium smegmatis [1].

1: Mycobacterium tuberculosis FtsX extracellular domain activates the peptidoglycan hydrolase, RipC. Mavrici D, Marakalala MJ, Holton JM, Prigozhin DM, Gee CL, Zhang YJ, Rubin EJ, Alber T; Proc Natl Acad Sci U S A. 2014;111:8037-8042. PMID:24843173