In this MPhil thesis research, a 29-residue peptide fragment from the N-terminal of the minimal activation domain, denoted as NckSa( 145-173) encompassing amino acid residues Gln145 to Asp173 of NckSa was demonstrated to bind to Cdk5 and hence resulting in kinase inhibition. In addition, this peptide could also inhibit Cdk2 with a similar potency as it does to Cdk5. The direct competition experiment showed that a synthetic peptide, NckSa( 146-173) does not compete with NckSa for Cdk5. Steady state kinetic analysis indicated that the Nck5a(146-173) peptide acts as a non-competitive inhibitor of CdkS/NckSa complex with respect to its substrate. To understand the molecular basis of kinase inhibition by the peptide, we have determined the structure of peptide in solution by circular dichroi...[ Read more ]

In this MPhil thesis research, a 29-residue peptide fragment from the N-terminal of the minimal activation domain, denoted as NckSa( 145-173) encompassing amino acid residues Gln145 to Asp173 of NckSa was demonstrated to bind to Cdk5 and hence resulting in kinase inhibition. In addition, this peptide could also inhibit Cdk2 with a similar potency as it does to Cdk5. The direct competition experiment showed that a synthetic peptide, NckSa( 146-173) does not compete with NckSa for Cdk5. Steady state kinetic analysis indicated that the Nck5a(146-173) peptide acts as a non-competitive inhibitor of CdkS/NckSa complex with respect to its substrate. To understand the molecular basis of kinase inhibition by the peptide, we have determined the structure of peptide in solution by circular dichroism and two-dimensional ¹H NMR spectroscopy. The peptide segment adopts an amphipathic a-helical structure from residues Ser149 to Arg162. Four leucine residues and one phenylalanine residue clustered on the hydrophobic face of the helix, and this hydrophobic face is likely to be the contact area when the peptide binds to Cdk5 and Cdk2. Mutation experiments have also indicated that the C-terminal end of the peptide is also actively involved in the inhibition of Cdk5 and Cdk2.