Component of the Dot/Icm type IVB secretion system (T4BSS), which is used to inject bacterial effector proteins into eukaryotic host cells (By similarity). Part of a subcomplex which recruits effector proteins and delivers them to the core transmembrane subcomplex (By similarity). Is a critical subunit for binding a subset of effector proteins (By similarity). Recognizes more than one type of binding motif (By similarity). May be a critical factor that confers host specificity (By similarity). Necessary for full virulence of the bacterium in guinea pigs and presumably humans (PubMed:12704109). The T4BSS is a complex nanomachine composed of several subcomplexes. This subunit is part of the Type IV Coupling Complex (T4CC), a subcomplex composed of the DotLMNYZ core and the IcmSW-LvgA adapter subunits, linked by the C-terminal tail of DotL. At least some of the protein may be surface expressed. Shows attenuated virulence in guinea pigs. Mutant invades alveolar macrophages normally, but shows slower growth than wild-type strain. The mutant is twofold more susceptible to killing by human beta-defensin 2 but not to killing by other cationic peptides, serum complement, or polymorphonuclear neutrophils.