This is the periplasmic domain of YidC, a bacterial membrane protein which is required for the insertion and assembly of inner membrane proteins [1,2].

1: The crystal structure of the periplasmic domain of the Escherichia coli membrane protein insertase YidC contains a substrate binding cleft. Ravaud S, Stjepanovic G, Wild K, Sinning I; J Biol Chem. 2008;283:9350-9358. PMID:18234665

2: Crystal structure of the major periplasmic domain of the bacterial membrane protein assembly facilitator YidC. Oliver DC, Paetzel M; J Biol Chem. 2008;283:5208-5216. PMID:18093969