Crystal structure of the homolog of the oncoprotein gankyrin, an interactor of Rb and CDK4/6.
The oncoprotein gankyrin plays a central role in tumorigenesis and cell proliferation. Gankyrin interacts with the retinoblastoma tumor suppressor (Rb) and cyclin-dependent kinase 4/6 (CDK4/6), increases phosphorylation at specific residues of Rb by CDK4/6 in vivo, and promotes tumorigenesis. The phosphorylation of Rb by CDK4/6 leads to the deregulation of the cell cycle during G1/S transition. Although how phosphorylation occurs on Rb has been studied extensively, the mechanism of site-specific phosphorylation of Rb remains unclear due to a lack of information on the structural arrangement of Rb and CDK4/6. Here, we have determined and refined to 2.3-A resolution the crystal structure of a gankyrin homolog, the non-ATPase subunit 6 (Nas6p) of the proteasome from yeast. The crystal structure reveals that Nas6p contains seven ankyrin repeats. The number of the repeats is different from that predicted from the primary structure. Nas6p also possesses an unusual curved structure with two acidic regions at the N- and C-terminal regions separated by one basic region, suggesting that it has at least two functional surfaces. The tertiary structure of Nas6p, together with the previous biochemical studies, indicates that the CDK4/6 and Rb binding surfaces of gankyrin are located at the N- and C-terminal regions, respectively, and face the same side of gankyrin. These observations suggest that gankyrin brings Rb and CDK4/6 together through gankyrin-Rb and gankyrin-CDK4/6 interactions and determines the relative positioning of the substrate (Rb) and the enzyme (CDK4/6). Our findings provide mechanistic insight into site-specific phosphorylation of Rb caused by CDK4/6.
Horikoshi Gene Selector Project, Exploratory Research for Advanced Technology, Japan Science and Technology Corp., 5-9-6 Tokodai, Tsukuba, Ibaraki 300-2635, Japan.
Balasundaram
B
Padmanabhan
Naruhiko
N
Adachi
Kazuhiro
K
Kataoka
Masami
M
Horikoshi
D000595:Amino Acid Sequence; D002453:Cell Cycle; D018360:Crystallography, X-Ray; D051358:Cyclin-Dependent Kinase 4; D051361:Cyclin-Dependent Kinase 6; D018844:Cyclin-Dependent Kinases / Q000037:antagonists & inhibitors*; D005656:Fungal Proteins / Q000737:chemistry; D008958:Models, Molecular; D008969:Molecular Sequence Data; D015513:Oncogene Proteins / Q000737:chemistry*; D010766:Phosphorylation; D046988:Proteasome Endopeptidase Complex; D011485:Protein Binding; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000737:chemistry* / Q000378:metabolism; D011518:Proto-Oncogene Proteins; D016160:Retinoblastoma Protein / Q000037:antagonists & inhibitors* / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins; D017386:Sequence Homology, Amino Acid
D005656:Fungal Proteins; C114551:NAS6 protein, S cerevisiae; D015513:Oncogene Proteins; C403591:PSMD10 protein, human; D011506:Proteins; D011518:Proto-Oncogene Proteins; D016160:Retinoblastoma Protein; D029701:Saccharomyces cerevisiae Proteins; D051358:Cyclin-Dependent Kinase 4; D051361:Cyclin-Dependent Kinase 6; D018844:Cyclin-Dependent Kinases; D046988:Proteasome Endopeptidase Complex