Atul K Srivastava
Department of Biochemistry, Molecular Biology and Biophysics,
University of Minnesota, MN-55455
Protein kinases regulate eukaryotic cellular processes via phosphorylation of suitable substrates, and act as signal transducing agents to orchestrate complex cellular activities. Cyclic-AMP-dependent protein kinase A was the first kinase to be crystallized and has been the subject of extensive research. Its structural dynamics is finely tuned to recognize and phosphorylate a variety of substrates. We have investigated the dynamical characteristics of the nucleotide-bound forms of the catalytic subunit of wildtype kinase (PKA-C) and the PKA mutant Y204A to understand the factors responsible for the catalytic efficiency and allostery in PKA. The mutation Y204A, though not directly involved in interactions with the substrate or the nucleotide, severely degrades the enzyme’s catalytic efficiency. We show that conformational dynamics, but not the structure, is altered due to the mutation and the perturbation radiates to the distal part of the protein revealing that allostery is governed by the structural fluctuations. Also,
ADP release via the opening of the enzyme (the rate limiting step in catalysis) is altered as the motion becomes asynchronous in the mutant. These results demonstrate that PKA conformational dynamics contributes to the enzyme’s allostery and catalytic process and has been optimized for enzymatic activity and regulation.