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LSSS 2014-2015

2014LSSS2015

Life Sciences Seminar Series

 

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Andrea Musacchio

Department of Mechanistic Cell Biology, Max-Planck Institute of Molecular Physiology, Dortmund, Germany

The molecular machinery of chromosome segregation and its feedback control

Selected Publications

The pseudo GTPase CENP-M drives human kinetochore assembly.Basilico F, Maffini S, Weir JR, Prumbaum D, Rojas AM, Zimniak T, De Antoni A, Jeganathan S, Voss B, van Gerwen S, Krenn V, Massimiliano L, Valencia A, Vetter IR, Herzog F, Raunser S, Pasqualato S, Musacchio A
Elife 2014; 3:e02978

Abstract

Kinetochores, multi-subunit complexes that assemble at the interface with centromeres, bind spindle microtubules to ensure faithful delivery of chromosomes during cell division. The configuration and function of the kinetochore-centromere interface is poorly understood. We report that a protein at this interface, CENP-M, is structurally and evolutionarily related to small GTPases but is incapable of GTP-binding and conformational switching. We show that CENP-M is crucially required for the assembly and stability of a tetramer also comprising CENP-I, CENP-H, and CENP-K, the HIKM complex, which we extensively characterize through a combination of structural, biochemical, and cell biological approaches. A point mutant affecting the CENP-M/CENP-I interaction hampers kinetochore assembly and chromosome alignment and prevents kinetochore recruitment of the CENP-T/W complex, questioning a role of CENP-T/W as founder of an independent axis of kinetochore assembly. Our studies identify a single pathway having CENP-C as founder, and CENP-H/I/K/M and CENP-T/W as CENP-C-dependent followers.DOI: http://dx.doi.org/10.7554/eLife.02978.001.

Modular assembly of RWD domains on the Mis12 complex underlies outer kinetochore organization.Petrovic A, Mosalaganti S, Keller J, Mattiuzzo M, Overlack K, Krenn V, De Antoni A, Wohlgemuth S, Cecatiello V, Pasqualato S, Raunser S, Musacchio A
Mol. Cell 2014 Feb 20; 53(4):591-605

Abstract

Faithful chromosome segregation is mandatory for cell and organismal viability. Kinetochores, large protein assemblies embedded in centromeric chromatin, establish a mechanical link between chromosomes and spindle microtubules. The KMN network, a conserved 10-subunit kinetochore complex, harbors the microtubule-binding interface. RWD domains in the KMN subunits Spc24 and Spc25 mediate kinetochore targeting of the microtubule-binding subunits by interacting with the Mis12 complex, a KMN subcomplex that tethers directly onto the underlying chromatin layer. Here, we show that Knl1, a KMN subunit involved in mitotic checkpoint signaling, also contains RWD domains that bind the Mis12 complex and that mediate kinetochore targeting of Knl1. By reporting the first 3D electron microscopy structure of the KMN network, we provide a comprehensive framework to interpret how interactions of RWD-containing proteins with the Mis12 complex shape KMN network topology. Our observations unveil a regular pattern in the construction of the outer kinetochore.

Bub3 reads phosphorylated MELT repeats to promote spindle assembly checkpoint signaling.Primorac I, Weir JR, Chiroli E, Gross F, Hoffmann I, van Gerwen S, Ciliberto A, Musacchio A
Elife 2013; 2:e01030

Abstract

Regulation of macromolecular interactions by phosphorylation is crucial in signaling networks. In the spindle assembly checkpoint (SAC), which enables errorless chromosome segregation, phosphorylation promotes recruitment of SAC proteins to tensionless kinetochores. The SAC kinase Mps1 phosphorylates multiple Met-Glu-Leu-Thr (MELT) motifs on the kinetochore subunit Spc105/Knl1. The phosphorylated MELT motifs (MELT(P)) then promote recruitment of downstream signaling components. How MELT(P) motifs are recognized is unclear. In this study, we report that Bub3, a 7-bladed β-propeller, is the MELT(P) reader. It contains an exceptionally well-conserved interface that docks the MELT(P) sequence on the side of the β-propeller in a previously unknown binding mode. Mutations targeting the Bub3 interface prevent kinetochore recruitment of the SAC kinase Bub1. Crucially, they also cause a checkpoint defect, showing that recognition of phosphorylated targets by Bub3 is required for checkpoint signaling. Our data provide the first detailed mechanistic insight into how phosphorylation promotes recruitment of checkpoint proteins to kinetochores. DOI:http://dx.doi.org/10.7554/eLife.01030.001.

Implications for kinetochore-microtubule attachment from the structure of an engineered Ndc80 complex.Ciferri C, Pasqualato S, Screpanti E, Varetti G, Santaguida S, Dos Reis G, Maiolica A, Polka J, De Luca JG, De Wulf P, Salek M, Rappsilber J, Moores CA, Salmon ED, Musacchio A
Cell 2008 May 2; 133(3):427-39

Abstract

Kinetochores are proteinaceous assemblies that mediate the interaction of chromosomes with the mitotic spindle. The 180 kDa Ndc80 complex is a direct point of contact between kinetochores and microtubules. Its four subunits contain coiled coils and form an elongated rod structure with functional globular domains at either end. We crystallized an engineered "bonsai" Ndc80 complex containing a shortened rod domain but retaining the globular domains required for kinetochore localization and microtubule binding. The structure reveals a microtubule-binding interface containing a pair of tightly interacting calponin-homology (CH) domains with a previously unknown arrangement. The interaction with microtubules is cooperative and predominantly electrostatic. It involves positive charges in the CH domains and in the N-terminal tail of the Ndc80 subunit and negative charges in tubulin C-terminal tails and is regulated by the Aurora B kinase. We discuss our results with reference to current models of kinetochore-microtubule attachment and centromere organization.

The Mad2 conformational dimer: structure and implications for the spindle assembly checkpoint.Mapelli M, Massimiliano L, Santaguida S, Musacchio A
Cell 2007 Nov 16; 131(4):730-43

Abstract

The 25 kDa Mad2 protein is a key player in the spindle assembly checkpoint, a safeguard against chromosome segregation errors in mitosis. Mad2 combines three unusual properties. First, Mad2 adopts two conformations with distinct topologies, open (O) and closed (C) Mad2. Second, C-Mad2 forms topological links with its two best-characterized protein ligands, Mad1 and Cdc20. Third, O-Mad2 and C-Mad2 engage in a "conformational" dimer that is essential for spindle checkpoint function in different organisms. The crystal structure of the O-Mad2-C-Mad2 conformational dimer, reported here, reveals an asymmetric interface that explains the selective dimerization of the O-Mad2 and C-Mad2 conformers. The structure also identifies several buried hydrophobic residues whose rearrangement correlates with the Mad2 topological change. The structure of the O-Mad2-C-Mad2 conformational dimer is consistent with a catalytic model in which a C-Mad2 template facilitates the binding of O-Mad2 to Cdc20, the target of Mad2 in the spindle checkpoint.