This entry is the BID (Bep intracellular delivery) domain located at the C-terminal of Bartonella effector proteins (Beps). It functions as a secretion signal in a subfamily of protein substrates of bacterial type IV secretion (T4S) systems. It mediates transfer of (1) relaxases and the attached DNA during bacterial conjugation, and (2) numerous Beps during protein transfer into host cells infected by pathogenic Bartonella species. Crystal structure of several representative BID domains show a conserved fold characterized by a compact, antiparallel four-helix bundle topped with a hook [1].

1: The BID Domain of Type IV Secretion Substrates Forms a Conserved Four-Helix Bundle Topped with a Hook. Stanger FV, de Beer TA, Dranow DM, Schirmer T, Phan I, Dehio C; Structure. 2017;25:203-211. PMID:27889208