Phosphoenolpyruvate carboxylase kinase is a novel protein kinase regulated at the level of expression

Abstract

Phosphorylation of phosphoenolpyruvate carboxylase plays a key role in the control of plant metabolism. Phosphoenolpyruvate carboxylase kinase is a Ca2+-independent enzyme that is activated by a process involving protein synthesis in response to a range of signals in different plant tissues. The component whose synthesis is required for activation has not previously been identified, nor has the kinase been characterised at a molecular level. We report the cloning of phosphoenolpyruvate carboxylase kinase from the Crassulacean Acid Metabolism plant Kalanchoë fedtschenkoi and the C3 plant Arabidopsis thaliana. Surprisingly, phosphoenolpyruvate carboxylase kinase is a member of the Ca2+/calmodulin-regulated group of protein kinases. However, it lacks the auto-inhibitory region and EF hands of plant Ca2+-dependent protein kinases, explaining its Ca2+-independence. Its sequence is novel in that it comprises only a protein kinase catalytic domain with no regulatory regions; it appears to be the smallest known protein kinase. In K. fedtschenkoi, the abundance of phosphoenolpyruvate carboxylase kinase transcripts increases during leaf development. The transcript level in mature leaves is very low during the photoperiod, reaches a peak in the middle of the dark period and correlates with kinase activity. It exhibits a circadian oscillation in constant conditions. Protein kinases are typically regulated by second messengers, phosphorylation or protein/protein interactions. Phosphoenolpyruvate carboxylase kinase is an exception to this general rule, being controlled only at the level of expression. In K. fedtschenkoi, its expression is controlled both developmentally and by a circadian oscillator.

Salt stress increases the Ca2+-independent phosphoenolpyruvate carboxylase kinase activity in Sorghum leaves

“…Collectively, these results are in good agreement with previous results Vidal et al 1996;Vidal and Chollet 1997;Hartwell et al 1999), and establish a Ca 2+ -independent PEPCase-kinase as the PEPCase-kinase speci®cally altered by NaCl treatment of illuminated Sorghum leaves.…”

“…This posttranslational control modulates the regulatory properties of PEPCase, notably by decreasing the sensitivity of the enzyme to its feedback inhibitor L-malate (Nimmo et al 1987). Based on the results obtained using a cellular approach, it has been proposed that this regulatory process is mediated by an intricate, light-signal transduction cascade leading to up-regulation of the PEPCase-kinase (Giglioli-Guivarc'h et al 1996) via protein synthesis (Jiao et al 1991;Hartwell et al 1999). This low-abundance, Ca 2+ -independent, 30-to 32-kDa ) serine/threonine kinase is thought to represent the genuine PEPCase-kinase .…”

Effect of LiCl on phosphoenolpyruvate carboxylase kinase and the phosphorylation of phosphoenolpyruvate carboxylase in leaf disks and leaves of Sorghum vulgare

“…Both bands were upregulated by light (Fig. 3a) and the molecular mass corresponded to those reported by others investigators (Li and Chollet 1994;Vidal and Chollet 1997;Hartwell et al 1999;Taybi et al 2000;Nimmo 2003). A further and signiWcant increase was seen in plants that had been treated for 1 week in the presence of LiCl (Fig.…”

Partial purification and biochemical characterization of a heteromeric protein phosphatase 2A holoenzyme from maize ( Zea mays L.) leaves that dephosphorylates C 4 phospho enol pyruvate carboxylase

“…Upon speci®c phosphorylation of plant PEPC at a strictly conserved serine (Ser) residue near its N-terminus by PEPC-kinase, this target enzyme is rendered both more active and more sensitive to allosteric activators such as glucose 6-phosphate (Glc6P), and less sensitive to feedback inhibition by L-malate. Recent molecular cloning of this dedicated serine/threonine (Ser/Thr) kinase con®rmed earlier biochemical ®ndings that the 32-kDa PEPC-kinase is Ca 2+ -independent since it lacks both the autoinhibitory domain and calmodulin-like EF hands of its closest homolog in plants, the Ca 2+ -dependent protein kinases (CDPKs) (Hartwell et al 1999;Nimmo 2000;Taybi et al 2000). While the biochemical characterization and cDNA cloning of PEPC-kinase have been pursued intensively, the requisite opposing enzyme, PEPC-phosphatase, has received much less attention.…”