Importance of threonine residues in the regulation of peanut serine/threonine/tyrosine protein kinase activity

Abstract

Protein tyrosine phosphorylation is carried out by dual-specificity kinases in plants. Peanut dual-specificity kinase has been shown to be regulated by tyrosine phosphorylation. However, the role of threonine residues in the regulation of peanut serine/threonine/tyrosine (STY) protein kinase is not yet documented. In the present study, we have investigated the role of threonine residues in the regulation of peanut STY protein kinase activity. The four threonine residues in the kinase activation loop and Thr 211 in the threonine-glutamate-tyrosine (TEY) motif were mutated to alanine to study their role in the regulation of kinase activity. The protein kinase activity was abolished when Thr 211 of TEY motif and Thr 296 of activation loop were converted to alanine, suggesting that they positively regulate the kinase activity. The ability of T211A and T296A to phosphorylate histone H1 was also reduced drastically. The other mutants T287A, T291A and T294A did not show any change in their ability to autophosphorylate or phosphorylate histone H1 when compared to wild-type peanut STY protein kinase. Data presented here suggests the importance of threonine residues in the regulation of peanut STY protein kinase activity and emphasizes the complexity of regulation of dual-specificity protein kinases in plants.