Two NEMO-like Ubiquitin-Binding Domains in CEP55 Differently Regulate Cytokinesis

CEP55 regulates the final critical step of cell division termed cytokinetic abscission. We report herein that CEP55 contains two NEMO-like ubiquitin-binding domains (UBDs), NOA and ZF, which regulate its function in a different manner. In vitro studies of isolated domains showed that NOA adopts a dimeric coiled-coil structure, whereas ZF is based on a UBZ scaffold. Strikingly, CEP55 knocked-down HeLa cells reconstituted with the full-length CEP55 ubiquitin-binding defective mutants, containing structure-guided mutations either in NOA^CEP55 or ZF^CEP55 domains, display severe abscission defects. In addition, the ZF^CEP55 can be functionally replaced by some ZF-based UBDs belonging to the UBZ family, indicating that the essential function of ZF^CEP55 is to act as ubiquitin receptor. Our work reveals an unexpected role of CEP55 in non-degradative ubiquitin signaling during cytokinetic abscission and provides a molecular basis as to how CEP55 mutations can lead to neurological disorders such as the MARCH syndrome.