title: Peptide phosphorylation by calcium-dependent protein kinase from maize seedlings.
abstract: Ca2+-dependent protein kinase (CDPK-1) was purified from maize seedlings, and its substrate specificity studied using a set of synthetic peptides derived from the phosphorylatable sequence RVLSRLHS15VRER of maize sucrose synthase 2. The decapeptide LARLHSVRER was found to be efficiently phosphorylated as a minimal substrate. The same set of peptides were found to be phosphorylated by mammalian protein kinase Cbeta (PKC), but showed low reactivity with protein kinase A (PKA). Proceeding from the sequence LARLHSVRER, a series of cellulose-membrane-attached peptides of systematically modified structure was synthesised. These peptides had hydrophobic (Ala, Leu) and ionic (Arg, Glu) amino acids substituted in each position. The phosphorylation of these substrates by CDPK-1 was measured and the substrate specificity of the maize protein kinase characterised by the consensus sequence motif A/L-5X-4R-3X-2X-1SX+1R+2Z+3R+4, where X denotes a position with no strict amino acid requirements and Z a position strictly not tolerating arginine compared with the other three varied amino acids. This motif had a characteristic sequence element RZR at positions +2 to +4 and closely resembled the primary structure of the sucrose synthase phosphorylation site. The sequence surrounding the phosphorylatable serine in this consensus motif was similar to the analogous sequence K/RXXS/TXK/R proposed for mammalian PKC, but different from the consensus motif RRXS/TX for PKA.
authors.affiliation: Institute of Chemical Physics, Tartu University, Estonia.
authors.forename: M
authors.initials: M
authors.lastname: Loog
authors.forename: R
authors.initials: R
authors.lastname: Toomik
authors.forename: K
authors.initials: K
authors.lastname: Sak
authors.forename: G
authors.initials: G
authors.lastname: Muszynska
authors.forename: J
authors.initials: J
authors.lastname: Järv
authors.forename: P
authors.initials: P
authors.lastname: Ek
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000302:isolation & purification / Q000378:metabolism*; D002847:Chromatography, Agarose / Q000379:methods; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000378:metabolism / Q000494:pharmacology; D008567:Membranes, Artificial; D008969:Molecular Sequence Data; D010455:Peptides / Q000138:chemical synthesis / Q000737:chemistry / Q000378:metabolism*; D010766:Phosphorylation; D010940:Plant Proteins / Q000302:isolation & purification / Q000378:metabolism*; D011493:Protein Kinase C / Q000378:metabolism; D012639:Seeds / Q000201:enzymology; D013379:Substrate Specificity; D003313:Zea mays / Q000201:enzymology*
chemical_list: D004791:Enzyme Inhibitors; D008567:Membranes, Artificial; D010455:Peptides; D010940:Plant Proteins; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D017871:Calcium-Calmodulin-Dependent Protein Kinases