Submitted to: Plant Journal
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/19/2007
Publication Date: 3/1/2008
Citation: Chastain, C.J., Xu, W., Parsley, K., Sarath, G., Hibberd, J.M., Chollet, R. 2008. The Arabidopsis pyruvate,orthophosphate dikinase regulatory proteins encode a novel, unprecedented Ser/Thr protein kinase primary structure. Plant Journal 53: 854-863. Interpretive Summary: Key enzymes involved in carbon-fixation by plants during photosynthesis as often regulated by several means. Many of these changes occur to the amino acid backbone of the protein and modulate its activity. Such changes will determine the rate at which carbon can be assimilated/or utilized by the plant. Enzymes involved in carbon metabolism are therefore critical for plant productivity. In this paper we have shown the activity and function of the protein regulator called Regulatory Protein (RP), of the enzyme Pyruvate,orthophosphate dikinase (PPDK). PPDK is a key component for carbon metabolism by plants. Identification of RP could lead to better understanding of the role of PPDK in non-photosynthetic cells and to the efficient manipulation of plant metabolism in the future.
Technical Abstract: Pyruvate,orthophosphate dikinase (PPDK) is a ubiquitous, low abundance metabolic enzyme of undetermined function in C3 plants. Its activity in C3 chloroplasts is light-regulated via reversible phosphorylation of an active-site Thr residue by the PPDK regulatory protein (RP), a most unusual, bifunctional protein kinase (PK)/protein phosphatase (PP). In this report we document the molecular cloning and functional analysis of the two unique C3 RPs in Arabidopsis thaliana. The first of these, AtRP1, encodes a typical chloroplast-targeted, bifunctional C4-like RP. The second RP gene, AtRP2, encodes a monofunctional polypeptide that possesses in vitro RP-like PK-activity but lacks PP-activity, and is localized in the cytosol. Although both C3 RP enzymes are functionally Ser/Thr kinases, the deduced primary structures of these two polypeptides are notably devoid of any canonical subdomain structure that unifies all known eukaryotic and prokaryotic Ser/Thr PKs into one of three superfamilies. Instead, these C3 RPs and the related C4-plant homologues encode a conserved, centrally positioned, ~260-residue sequence currently described as the “domain of unknown function 299”. We propose that vascular plant RP represents the first functionally identified member of a novel protein kinase family presently designated as the DUF 299 gene family.