This domain is found in PilN type IV pilus biogenesis protein present in Thermus thermophiles. PilN is an integral inner membrane protein needed for the formation of type IV pilus. This domain forms a dimer which is mediated by symmetric contacts between residues in alpha-1, beta-1, beta-3 and alpha-3 [1].

1: Structure and assembly of an inner membrane platform for initiation of type IV pilus biogenesis. Karuppiah V, Collins RF, Thistlethwaite A, Gao Y, Derrick JP; Proc Natl Acad Sci U S A. 2013;110:E4638-E4647. PMID:24218553