IcmL contains two amphipathic beta-sheet regions, required for the pore-forming ability which may be related to the transfer of this protein into a host cell membrane [1]. The icmL gene shows significant similarity to plasmid genes involved in conjugation however IcmL is thought to be required for macrophage killing. It is unknown whether conjugation plays a role in macrophage killing [2]. This is a family of DotI/IcmL proteins of type IVb secretion systems, that reside in the inner-membrane. It carries a single transmembrane helix in the N-terminal conserved region, has an extra-periplasmic domain, and is conserved in all T4BSSs including I-type conjugation systems (TraM). DotI/IcmL (and DotJ) may form an inner membrane complex that associates with the core complex [3].

1: How is the intracellular fate of the Legionella pneumophila phagosome determined?. Segal G, Shuman HA; Trends Microbiol. 1998;6:253-255. PMID:9717210

2: Host cell killing and bacterial conjugation require overlapping sets of genes within a 22-kb region of the Legionella pneumophila genome. Segal G, Purcell M, Shuman HA; Proc Natl Acad Sci U S A. 1998;95:1669-1674. PMID:9465074

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