Serine/threonine/tyrosine protein kinase from Arabidopsis thaliana is dependent on serine residues for its activity.

Genome-wide analysis of Arabidopsis thaliana with tyrosine kinase motif from animals predicted that tyrosine phosphorylation could be brought about only by dual-specificity protein kinases in plants. However, their regulation is poorly understood. In the present study, we have investigated the role of serines required for the activity of Arabidopsis thaliana serine/threonine/tyrosine protein kinase (AtSTYPK). There are eight serines in the kinase catalytic domain. The role of each serine residue was studied individually by substituting them with alanine. Serines at positions 215, 259, 269 and 315 are required for the kinase activity both in terms of auto and substrate phosphorylations of myelin basic protein. The mutant S265A showed slight increase in auto and substrate phosphorylations. Other serines at positions 165, 181 and 360 did not show any change in the phosphorylation status as compared to wild-type. In conclusion, these results suggest the importance of serine residues required for dual-specificity protein kinase activity.