Substrate Specificity of Cyclins Determined by Electrostatics

Abstract

ACKnowLeDGementSBII and IMCB are A-STAR institutes funded by BMRC. We thank Michael Schaefer for providing us with unpublished parameters for version 3 of the analytical continuum solvent method. AbStrACtCyclin dependent kinases (CDK) associate with cyclins to regulate cell cycle progression and gene transcription by phosphorylating key proteins. The different cyclin-CDK complexes display differences in substrate specificities with substrates binding across a shallow, hydrophobic and substrate-binding pocket known as the cyclin groove. However the mechanism underlying this differential substrate recognition remains largely unknown and cannot be explained merely on the basis of sequence variability. A subset of cyclins, cyclins A2, E1 and B1 despite being structurally and functionally similar, show marked differences in their interactions with recruitment peptides derived from their substrate or inhibitor proteins p27, p21, p57, E2F1, p53, pRb and p107. While these peptides (characterized by a cyclin binding motif of four residues ZRXL where Z and X are cationic residues) inhibit the activity of cyclins A2 and E1, no such inhibition is observed for cyclin B1.Electrostatic potentials of cyclins A2, E1 and B1 show that anionic regions of cyclins A2 and E1 enable them to bind peptides while cationic regions at homologous locations in cyclin B1 abrogate binding. These arise from charged residues that are conserved. Mutations that switch these characters are suggested. Computed energetics of binding confirms this. Deregulation of the enzymatic activity of this class of enzymes is a ubiquitous feature of human neoplasia, but attempts to exploit this therapeutically have been confounded by a lack of understanding of the precise specificity of the different cyclin complexes. Here we begin to clarify this issue by explaining the mechanism by which cyclin B1 escapes regulation by the p21 family of CDKIs.

C. elegansmitotic cyclins have distinct as well as overlapping functions in chromosome segregation

“…Although additional domains may be involved, these differences between CYB-1 and CYB-3 probably affect substrate specificity, as they concern the only substrate-docking site in cyclins known to date. 47 …”

Overexpression of a novel osteopetrosis-related gene CCDC154 suppresses cell proliferation by inducing G2/M arrest

“…the function of regulating the cyclin-Cdk kinase activity and inducing G 2 /M arrest. 24,25 We showed that overexpression of CCDC154 significantly reduced cyclin B1 and induced G 2 /M cell cycle arrest. These results, consistent with previous reports, imply that the cyclin-binding motifs play a critical role in cell growth regulation.…”

Cyclin J–CDK complexes limit innate immune responses by reducing proinflammatory changes in macrophage metabolism

“…These proinflammatory roles of cyclin-CDK signaling occur through the control of gene expression (15)(16)(17), suggesting that this is largely independent from their role in cell cycle regulation in macrophages and neutrophils. Because CDK functions largely depend on their cyclin partner for substrate recognition (21,22), it is therefore reasonable to hypothesize that cyclins serve as de facto regulators of CDK activity in immune responses.…”