This is the C-terminal domain of PilJ, a Type IV pilin found in gram-positive Clostridium difficile. Incorporation of PilJ into pili exposes the C-terminal domain of PilJ to create a novel interaction surface. This C-terminal domain is not observed in other Type IV pilin proteins [1].

1: Structure of Clostridium difficile PilJ exhibits unprecedented divergence from known type IV pilins. Piepenbrink KH, Maldarelli GA, de la Pena CF, Mulvey GL, Snyder GA, De Masi L, von Rosenvinge EC, Gunther S, Armstrong GD, Donnenberg MS, Sundberg EJ; J Biol Chem. 2014;289:4334-4345. PMID:24362261