title: The role of the LH subdomain in the function of the Cip/Kip cyclin-dependent kinase regulators.
abstract: The Cip/Kip protein family, which includes p27, p21, and p57, modulates the activity of cyclin-dependent kinases (Cdks). A domain within these proteins, termed the kinase inhibitory domain (KID), is necessary and sufficient for Cdk inhibition. The KID consists of a cyclin-binding subdomain (termed D1) and a Cdk-binding subdomain (termed D2) joined by a 22-residue linker subdomain (termed LH). Before binding the Cdks, D1 and D2 are largely unstructured and the LH subdomain exhibits nascent helical characteristics. Curiously, although the sequence of the linker subdomain is not highly conserved within the family, its nascent helical structure is conserved. In this study, we explored the role of this structural conservation in interactions with cyclin-dependent kinase 2 (Cdk2) and cyclin A. We constructed chimeric p27-KID molecules in which the p27 LH subdomain was replaced with the corresponding segments of either p21 or p57. The chimeric molecules bind and inhibit Cdk2 in a manner similar to wild-type p27-KID. However, the extent of enthalpy/entropy compensation associated with these interactions was dramatically different, indicating different extents of LH subdomain folding upon binding. Our results indicate that the different LH subdomains, despite their sequence and thermodynamic differences, play similar roles in binding and inhibiting Cdk2/cyclin A.
authors.affiliation: Department of Structural Biology, St. Jude Children's Research Hospital, Memphis, Tennessee, USA.
authors.forename: Steve
authors.initials: S
authors.lastname: Otieno
authors.forename: Christy R
authors.initials: CR
authors.lastname: Grace
authors.forename: Richard W
authors.initials: RW
authors.lastname: Kriwacki
mesh_terms: D000595:Amino Acid Sequence; D002151:Calorimetry; D002942:Circular Dichroism; D019925:Cyclin A / Q000737:chemistry / Q000378:metabolism; D051357:Cyclin-Dependent Kinase 2 / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000737:chemistry* / Q000378:metabolism*; D050760:Cyclin-Dependent Kinase Inhibitor p27 / Q000737:chemistry* / Q000378:metabolism*; D050761:Cyclin-Dependent Kinase Inhibitor p57 / Q000737:chemistry* / Q000378:metabolism*; D006801:Humans; D020128:Inhibitory Concentration 50; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D050505:Mutant Proteins / Q000378:metabolism; D011485:Protein Binding; D055550:Protein Stability; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D013329:Structure-Activity Relationship; D044366:Transition Temperature
chemical_list: D019925:Cyclin A; D050759:Cyclin-Dependent Kinase Inhibitor p21; D050761:Cyclin-Dependent Kinase Inhibitor p57; D050505:Mutant Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; D051357:Cyclin-Dependent Kinase 2