Component of the Dot/Icm type IVB secretion system (T4BSS), which is used to inject bacterial effector proteins into eukaryotic host cells (PubMed:32513920, PubMed:28714967, PubMed:32457311). Part of a subcomplex which recruits effector proteins and delivers them to the core transmembrane subcomplex (PubMed:32513920, PubMed:32457311). Is a critical subunit for binding a subset of effector proteins (PubMed:28714967, PubMed:32457311). Recognizes more than one type of binding motif (PubMed:32457311). May be a critical factor that confers host specificity (PubMed:16803597). 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 (PubMed:28714967, PubMed:32457311, PubMed:32513920). Interacts with DotL, IcmS and IcmW (PubMed:28714967, PubMed:16803597). Interacts with various effector proteins, including VpdB, SetA, PieA and SidH (PubMed:32457311). Constitutively expressed in vitro. Mutant is differentially attenuated in diverse hosts (PubMed:16803597). Inactivation of the gene causes a minimal defect in growth in the human monocytic cell line U937 and the environmental host A.castellanii, but mutant is severely attenuated for intracellular growth in mouse macrophages (PubMed:16803597). Mutant appears to assemble a fully functional Dot/Icm complex and exhibits wild-type levels of contact-dependent cytotoxicity (PubMed:16803597).