3v7d
Crystal Structure of ScSkp1-ScCdc4-pSic1 peptide complex
Structural highlights
FunctionSKP1_YEAST Essential component of the E3 ubiquitin ligase complex SCF (SKP1-CUL1-F-box protein) ubiquitin ligase complex, which mediates the ubiquitination and subsequent proteasomal degradation of target proteins like phosphorylated SIC1. Participates in the attachment of chromosomes to the spindle. Acts as a regulatory component of the centromere DNA-binding protein complex CBF3, which is essential for chromosome segregation and movement of centromeres along microtubules. CBF3 is required for the recruitment of other kinetochore complexes to CEN DNA. It plays a role in the attachment of chromosomes to the spindle and binds selectively to a highly conserved DNA sequence called CDEIII, found in centromeres and in several promoters. The association of CBF3C with CBF3D and SGT1 is required for CBF3C activation and CBF3 assembly. SKP1/CBF3D could retrieve cyclins or cyclin-CDK-like proteins into the kinetochore thus providing cell cycle-regulated kinetochore activity. Involved in the regulation of methionine biosynthesis genes. Facilitates association of CDC53 with CDC4 and of ROY1 with YPT52.[1] [2] [3] [4] [5] [6] [7] Publication Abstract from PubMedThe ubiquitin ligase SCF(Cdc4) (Skp1/Cul1/F-box protein) recognizes its substrate, the cyclin-dependent kinase inhibitor Sic1, in a multisite phosphorylation-dependent manner. Although short diphosphorylated peptides derived from Sic1 can bind to Cdc4 with high affinity, through systematic mutagenesis and quantitative biophysical analysis we show that individually weak, dispersed Sic1 phospho sites engage Cdc4 in a dynamic equilibrium. The affinities of individual phosphoepitopes serve to tune the overall phosphorylation site threshold needed for efficient recognition. Notably, phosphoepitope affinity for Cdc4 is dramatically weakened in the context of full-length Sic1, demonstrating the importance of regional environment on binding interactions. The multisite nature of the Sic1-Cdc4 interaction confers cooperative dependence on kinase activity for Sic1 recognition and ubiquitination under equilibrium reaction conditions. Composite dynamic interactions of low affinity sites may be a general mechanism to establish phosphorylation thresholds in biological responses. Composite low affinity interactions dictate recognition of the cyclin-dependent kinase inhibitor Sic1 by the SCFCdc4 ubiquitin ligase.,Tang X, Orlicky S, Mittag T, Csizmok V, Pawson T, Forman-Kay JD, Sicheri F, Tyers M Proc Natl Acad Sci U S A. 2012 Feb 28;109(9):3287-92. Epub 2012 Feb 10. PMID:22328159[8] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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