This domain is found in the major pilin protein PilA. PilA4 binds to PilMNO forming a complex with a well-defined platform linking the cytoplasmic PilM protein to pilus subunits in the periplasm. Structure analysis indicate that it is comprised of one alpha-helix and 4 beta-sheets [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