The obligate intracellular pathogen Legionella pneumophila requires a T4bSS, known as the Dot/Icm secretion system or translocase, for growth in alveolar macrophages. It is encoded by roughly 26 dot/icm genes and its main job is to export protein effectors into the cytoplasm of host cells during infection. Many of the constituting proteins share sequence homology to genes in other bacterial conjugation system; however, others, such as IcmR and IcmQ do not and therefore are thought to have a unique role in this secretion system. IcmQ has been shown to associate with IcmR, bind to membranes and have a critical role in the T4bSS PMID:23850453,PMID:15661013.

Structural domains comprising this superfamily share the structure of the C-terminal domain of IcmQ (Qc). Qc presents a novel NAD+ binding fold and it is believed that this causes it to as a sensor which allows IcmR-IcmQ to interact with a critical component of the T4bSS when intracellular NAD+ levels are sufficient for binding PMID:23850453.