Crystal structure and mutational analysis of the Saccharomyces cerevisiae cell cycle regulatory protein Cks1: implications for domain swapping, anion binding and protein interactions.
BACKGROUND
The Saccharomyces cerevisiae protein Cks1 (cyclin-dependent kinase subunit 1) is essential for cell-cycle progression. The biological function of Cks1 can be modulated by a switch between two distinct molecular assemblies: the single domain fold, which results from the closing of a beta-hinge motif, and the intersubunit beta-strand interchanged dimer, which arises from the opening of the beta-hinge motif. The crystal structure of a cyclin-dependent kinase (Cdk) in complex with the human Cks homolog CksHs1 single-domain fold revealed the importance of conserved hydrophobic residues and charged residues within the beta-hinge motif.


RESULTS
The 3.0 A resolution Cks1 structure reveals the strict structural conservation of the Cks alpha/beta-core fold and the beta-hinge motif. The beta hinge identified in the Cks1 structure includes a novel pivot and exposes a cluster of conserved tyrosine residues that are involved in Cdk binding but are sequestered in the beta-interchanged Cks homolog suc1 dimer structure. This Cks1 structure confirms the conservation of the Cks anion-binding site, which interacts with sidechain residues from the C-terminal alpha helix of another subunit in the crystal.


CONCLUSIONS
The Cks1 structure exemplifies the conservation of the beta-interchanged dimer and the anion-binding site in evolutionarily distant yeast and human Cks homologs. Mutational analyses including in vivo rescue of CKS1 disruption support the dual functional roles of the beta-hinge residue Glu94, which participates in Cdk binding, and of the anion-binding pocket that is located 22 A away and on an opposite face to Glu94. The Cks1 structure suggests a biological role for the beta-interchanged dimer and the anion-binding site in targeting Cdks to specific phosphoproteins during cell-cycle progression.
Bourne
Y
Y
Centre National de la Recherche Scientifique, Marseille, France. yves@afmb.cnrs-mrs.fr
Watson
M H
MH
Arvai
A S
AS
Bernstein
S L
SL
Reed
S I
SI
Tainer
J A
JA
D048868:Adaptor Proteins, Signal Transducing; D000595:Amino Acid Sequence; D000838:Anions / Q000378:metabolism; D002453:Cell Cycle; D018797:Cell Cycle Proteins; D004252:DNA Mutational Analysis; D005656:Fungal Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006801:Humans; D008969:Molecular Sequence Data; D011485:Protein Binding; D011487:Protein Conformation; D012441:Saccharomyces cerevisiae; D029701:Saccharomyces cerevisiae Proteins
D048868:Adaptor Proteins, Signal Transducing; D000838:Anions; C081185:CKS1 protein, S cerevisiae; D018797:Cell Cycle Proteins; D005656:Fungal Proteins; D029701:Saccharomyces cerevisiae Proteins