Role of threonine residues in the regulation of manganese-dependent arabidopsis serine/threonine/tyrosine protein kinase activity

Abstract

Tyrosine phosphorylation in plants could be performed only by dual-specificity kinases. Arabidopsis thaliana dual-specificity protein kinase (AtSTYPK) exhibited strong preference for manganese over magnesium for its kinase activity. The kinase autophosphorylated on serine, threonine and tyrosine residues and phosphorylated myelin basic protein on threonine and tyrosine residues. The AtSTYPK harbors manganese dependent serine/threonine kinase domain, COG3642. His²⁴⁸ and Ser²⁶⁵ on COG3642 are conserved in AtSTYPK and the site-directed mutant, H248A showed loss of serine/threonine kinase activity. The protein kinase activity was abolished when Thr²⁰⁸ in the TEY motif and Thr²⁹³ of the activation loop were converted to alanine. The conversion of Thr²⁸⁴ in the activation loop to alanine resulted in an increased phosphorylation. This study reports the first identification of a manganese dependent dual-specificity kinase and the importance of Thr²⁰⁸, Thr²⁸⁴, and Thr²⁹³ residues in the regulation of kinase activity.