This is the greater N-terminal region of GspC-type proteins. GspC proteins form part of the sophisticated transport mechanism of Gram-negative pathogens for injecting divers proteins into their hosts, a type-II secretion system - T2SS. The region is made up of a short N-terminal cytoplasmic domain that is followed by the single transmembrane helix, a Pro-rich linker, and the so-called homology region domain in the periplasm. This inner membrane GspC interacts with the outer membrane secretin GspD via periplasmic domains, an interaction which is critical for the effectiveness of type II secretion [1].

1: Structural and functional studies on the interaction of GspC and GspD in the type II secretion system. Korotkov KV, Johnson TL, Jobling MG, Pruneda J, Pardon E, Heroux A, Turley S, Steyaert J, Holmes RK, Sandkvist M, Hol WG; PLoS Pathog. 2011;7:e1002228. PMID:21931548