This is a family of Gram-negative bacterial proteins involved in the Dot/Icm type IVb transport system. Members are small acidic cytoplasmic proteins required for Dot/Icm-dependent activities. Binary complexes of IcmW-IcmS and of IcmS-LvgA have been consistently reported, suggestive of the binary WXG100 system. The IcmW-IcmS complex may play a role in recruitment of effector proteins to the transport apparatus [1].

1: Type IVB Secretion Systems of Legionella and Other Gram-Negative Bacteria. Nagai H, Kubori T; Front Microbiol. 2011;2:136. PMID:21743810