Tumor Susceptibility Gene 101 (TSG101) Is a Novel Binding-Partner for the Class II Rab11-FIPs

The Rab11-FIPs (Rab11-family interacting proteins; henceforth, FIPs) are a family of Rab11a/Rab11b/Rab25 GTPase effector proteins implicated in an assortment of intracellular trafficking processes. Through proteomic screening, we have identified TSG101 (tumor susceptibility gene 101), a component of the ESCRT-I (endosomal sorting complex required for transport) complex, as a novel FIP4-binding protein, which we find can also bind FIP3. We show that alpha-helical coiled-coil regions of both TSG101 and FIP4 mediate the interaction with the cognate protein, and that point mutations in the coiled-coil regions of both TSG101 and FIP4 abrogate the interaction. We find that expression of TSG101 and FIP4 mutants cause cytokinesis defects, but that the TSG101-FIP4 interaction is not required for localisation of TSG101 to the midbody/Flemming body during abscission. Together, these data suggest functional overlap between Rab11-controlled processes and components of the ESCRT pathway.