Biology subjects

Maffini, S.

Publications and source records attributed to Maffini, S..

5 recordsLinked to original sources

bioRxiv2022

Targeting oncogenic KRasG13C with nucleotide-based covalent inhibitors

Mutations within Ras proteins represent major drivers in human cancer. In this study, we report the structure-based design, synthesis, as well as biochemical and cellular evaluation of nucleotide-based covalent inhibitors for KRasG13C, an important oncogenic mutant of Ras that has not been successfully addressed in the past. Mass spectrometry experiments and kinetic studies reveal promising molecular properties of these covalent inhibitors, and X-ray crystallographic analysis has yielded the first reported crystal structures of KRasG13C covalently locked with these GDP analogues. Importantly, KRasG13C covalently modified with these inhibitors can no longer undergo SOS-catalysed nucleotide exchange. As a final proof-of-concept, we show that in contrast to KRasG13C, the covalently locked protein is unable to induce oncogenic signalling in cells, further highlighting the possibility of using nucleotide-based inhibitors with covalent warheads in KRasG13C-driven cancer.

cancer biology↗

bioRxiv2022

Conformational transitions of the mitotic adaptor Spindly underlie its interaction with Dynein and Dynactin

Cytoplasmic Dynein 1, or Dynein, is a microtubule minus-end directed motor. Dynein motility requires Dynactin and a family of activating adaptors that stabilize the Dynein-Dynactin complex and promote regulated interactions with cargo in space and time. How activating adaptors limit Dynein activation to specialized subcellular locales is unclear. Here, we reveal that Spindly, a mitotic Dynein adaptor at the kinetochore corona, exists natively in a closed conformation that occludes binding of Dynein-Dynactin to its CC1 box and Spindly motif. A structure-based analysis identified various mutations promoting an open conformation of Spindly that binds Dynein-Dynactin. A region of Spindly downstream from the Spindly motif and not required for cargo binding faces the CC1 box and stabilizes the intramolecular closed conformation. This region is also required for robust kinetochore localization of Spindly, suggesting that kinetochores promote Spindly activation to recruit Dynein. This mechanism may be paradigmatic for Dynein activation by other adaptors at various cellular locales.

biochemistry↗

bioRxiv2021

Structure of the RZZ complex and molecular basis of Spindly-driven corona assembly at human kinetochores

In metazoans, a {asymp}1 megadalton (MDa) super-complex comprising the Dynein-Dynactin adaptor Spindly and the ROD-Zwilch-ZW10 (RZZ) complex is the building block of a fibrous biopolymer, the kinetochore fibrous corona. The corona assembles on mitotic kinetochores to promote microtubule capture and spindle assembly checkpoint (SAC) signaling. We report here a high-resolution cryo-EM structure that captures the essential features of the RZZ complex, including a farnesyl binding site required for Spindly binding. Using a highly predictive in vitro assay, we demonstrate that the SAC kinase MPS1 is necessary and sufficient for corona assembly at supercritical concentrations of the RZZ-Spindly (RZZS) complex, and describe the molecular mechanism of phosphorylation-dependent filament nucleation. We identify several structural requirements for RZZS polymerization in rings and sheets. Finally, we identify determinants of kinetochore localization and corona assembly of Spindly. Our results describe a framework for the long-sought-for molecular basis of corona assembly on metazoan kinetochores.

biochemistry↗

bioRxiv2019

Electroporated recombinant proteins as tools for in vivo functional complementation, imaging, and chemical biology

Delivery of native or chemically modified recombinant proteins into mammalian cells shows promise for functional investigations and various technological applications, but concerns that sub-cellular localization and functional integrity of delivered proteins may be affected remain high. Here, we surveyed batch electroporation as a delivery tool for single polypeptides and multi-subunit protein assemblies of kinetochores, a spatially confined and well-studied subcellular structures. After electroporation in human cells, recombinant fluorescent Ndc80 and Mis12 multi-subunit complexes displayed native localization, physically interacted with endogenous binding partners, and functionally complemented depleted endogenous counterparts to promote mitotic checkpoint signaling and chromosome segregation. Farnesylation is required for kinetochore localization of the Dynein adaptor Spindly. In cells with chronically inhibited farnesyl transferase activity, in vitro farnesylation and electroporation reconstituted robust kinetochore localization of Spindly. Thus, electroporation is uniquely versatile for delivering synthetic and, as required, chemically modified functional mimics of endogenous proteins, and is therefore a promising tool for chemical and synthetic biology.

cell biology↗

bioRxiv2018

Kinetochore recruitment of CENP-F illustrates how paralog divergence shapes kinetochore composition and function

The metazoan proteins CENP-E and CENP-F are components of a fibrous layer of mitotic kinetochores named the corona. Several features suggest that CENP-E and CENP-F are paralogs: they are very large (approximately 2700 and 3200 residues, respectively), rich in predicted coiled-coil structure, C-terminally prenylated, and endowed with microtubule-binding sites at their termini. In addition, CENP-E contains an ATP-hydrolyzing motor domain that promotes microtubule plus-end directed motion. Here, we show that CENP-E and CENP- F are recruited to mitotic kinetochores independently of the Rod-Zwilch-ZW10 (RZZ) complex, the main corona constituent. We identify selective interactions of CENP-E and CENP-F respectively with BubR1 and Bub1, paralogous proteins involved in mitotic checkpoint control and chromosome alignment. While BubR1 is dispensable for kinetochore localization of CENP-E, Bub1 is stringently required for CENP-F localization. Through biochemical reconstitution, we demonstrate that the CENP-E:BubR1 and CENP-F:Bub1 interactions are direct and require similar determinants, a dimeric coiled-coil in CENP-E or CENP-F and a kinase domain in BubR1 or Bub1. Our findings are consistent with the existence of pseudo-symmetric, paralogous Bub1:CENP-F and BubR1:CENP-E axes, supporting evolutionary relatedness of CENP-E and CENP-F.

cell biology↗