Biochemical and functional characterization of PKS11, a
novel Arabidopsis protein kinase.
Gong D, Gong Z, Guo Y, Chen X, Zhu JK.
Department of Plant Sciences, University of Arizona, Tucson, Arizona 85721, USA.
The Arabidopsis SOS2 (Salt Overly Sensitive 2)-like protein kinases (PKS) are
novel protein kinases that contain an SNF1-like catalytic domain with a putative
activation loop and a regulatory domain with an FISL motif that binds calcium
sensors. Very little biochemical and functional information is currently
available on this family of kinases. Here we report on the expression of the
PKS11 gene, activation and characterization of the gene product, and transgenic
evaluation of its function in plants. PKS11 transcript was preferentially
expressed in roots of Arabidopsis plants. Recombinant glutathione S-transferase
fusion protein of PKS11 was inactive in substrate phosphorylation. However, the
kinase can be highly activated by a threonine 161 to aspartate substitution
(designated PKS11T161D) in the putative activation loop. Interestingly, PKS11
can also be activated by substitution of either a serine or tyrosine with
aspartate within the activation loop. Deletion of the FISL motif also resulted
in a slight activation of PKS11. PKS11T161D displayed an uncommon preference for
Mn(2+) over Mg(2+) for substrate phosphorylation and autophosphorylation. The
optimal pH and temperature values of PKS11T161D were determined to be 7.5 and 30
degrees C, respectively. The activated kinase showed substrate specificity, high
affinity, and catalytic efficiency for a peptide substrate p3 and for ATP. AMP
or ADP at concentrations from 10 microm to 1 mm did not activate PKS11T161D.
Transgenic Arabidopsis plants expressing PKS11T161D were more resistant to high
concentrations of glucose, suggesting the involvement of this protein kinase in
sugar signaling in plants. These results provide insights into the function as
well as regulation and biochemical properties of the PKS protein kinase.