The crystal structure of the Sgt1-Skp1 complex: the link between Hsp90 and both SCF E3 ubiquitin ligases and kinetochores

The essential cochaperone Sgt1 recruits Hsp90 chaperone activity to a range of cellular factors including SCF E3 ubiquitin ligases and the kinetochore in eukaryotes. In these pathways Sgt1 interacts with Skp1, a small protein that heterodimerizes with proteins containing the F-box motif. We have determined the crystal structure of the interacting domains of Saccharomyces cerevisiae Sgt1 and Skp1 at 2.8 Å resolution and validated the interface in the context of the full-length proteins in solution. The BTB/POZ domain of Skp1 associates with Sgt1 via the concave surface of its TPR domain using residues that are conserved in humans. Dimerization of yeast Sgt1 occurs via an insertion that is absent from monomeric human Sgt1. We identify point mutations that disrupt dimerization and Skp1 binding in vitro and find that the interaction with Skp1 is an essential function of Sgt1 in yeast. Our data provide a structural rationale for understanding the phenotypes of temperature-sensitive Sgt1 mutants and for linking Skp1-associated proteins to Hsp90-dependent pathways

Cnn1 inhibits the interactions between the KMN complexes of the yeast kinetochore

El pdf del artículo es la versión de autor.-- et al.Kinetochores attach the replicated chromosomes to the mitotic spindle and orchestrate their transmission to the daughter cells. Kinetochore-spindle binding and chromosome segregation are mediated by the multi-copy KNL1 Spc105, MIS12 Mtw1 and NDC80 Ndc80 complexes that form the so-called KMN network. KMN-spindle attachment is regulated by the AuroraB Ipl1 and MPS1 Mps1 kinases. It is unclear whether other mechanisms exist that support KMN activity during the cell cycle. Using budding yeast, we show that kinetochore protein Cnn1 localizes to the base of the Ndc80 complex and promotes a functionally competent configuration of the KMN network. Cnn1 regulates KMN activity in a spatiotemporal manner by inhibiting the interaction between its complexes. Cnn1 activity peaks in anaphase and is driven by the Cdc28, Mps1 and Ipl1 kinases. © 2012 Macmillan Publishers Limited. All rights reserved.P.D.W. acknowledges financial support from the Italian Association for Cancer Research (grant 8840). T.R.H. recognizes support from the N.I.H. (grant GM087461) and the American Cancer Society (grant IRG 58-006-50). T.U.T. acknowledges a Cancer Research U.K. senior fellowship and Wellcome Trust program grant. L.J.B. acknowledges a doctoral fellowship from the European School of Molecular Medicine.Peer Reviewe

Induction of metabolic syndrome by excess fructose consumption

Fructose is an important nutritive component of foods such as honey and fruit, but this easily available sweetener may contribute to increased caloric consumption from overeating. Fructose is now a major component of the Western diet, with increased consumption associated with obesity, metabolic syndrome, and cardiovascular disorders in observational and short-term intervention studies, mainly in animal models. Rodent studies have identifi ed possible mechanisms for the adverse effects of fructose when ingested in large amounts. Fructose promoted de novo lipogenesis, infl ammation, and increased sympathetic tone. These mechanisms induced hepatic insulin resistance, increased total and visceral fat mass with accumulation of ectopic fat in the liver and skeletal muscle, and dyslipidemia. Fructose reduced leptin and insulin signals for satiety, caused structural and functional damage to the heart and blood vessels, and disrupted the diversity of the gut microbiota. These early effects may initiate the development of the metabolic syndrome. Despite this evidence from rodents, there are few long-term intervention studies in humans, especially at a moderate dose. The defi nition of prudent fructose consumption is needed, but this will require carefully controlled dose–response studies in humans