Phosphorylation of the elongation factor 2: the fifth Ca2+/calmodulin-dependent system of protein phosphorylation.
Elongation factor 2 (EF-2) has been recently shown to be extensively phosphorylated in a Ca2+/calmodulin-dependent manner in extracts of mammalian cells (A. G. Ryazanov (1987) FEBS Lett. 214, 331-334). In the present study, we partially purified the protein kinase which phosphorylates EF-2 from rabbit reticulocytes. The molecular weight of the enzyme determined by gel filtration was about 140,000. Unlike the substrate, the EF-2 kinase had no affinity for RNA and therefore could be separated from EF-2 by chromatography on RNA-Sepharose. After chromatography on hydroxyapatite, the kinase activity became calmodulin-dependent. Two-dimensional separation of the phosphorylated EF-2 according to O'Farrell's technique revealed that there were two phosphorylation sites within the EF-2 molecule; in both cases, the phosphorylated amino acid was threonine. The EF-2 kinase differed from the four known types of Ca2+/calmodulin-dependent protein kinases. Thus, the system of EF-2 phosphorylation represents the novel (fifth) Ca2+/calmodulin-dependent system of protein phosphorylation. This system is supposed to be responsible for the regulation of the elongation rate of protein biosynthesis in eukaryotic cells.
Ryazanov
A G
AG
Institute of Protein Research, Academy of Sciences, Pushchino, Moscow Region.
Natapov
P G
PG
Shestakova
E A
EA
Severin
F F
FF
Spirin
A S
AS
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000494:pharmacology*; D002147:Calmodulin / Q000494:pharmacology*; D002845:Chromatography; D017886:Durapatite; D006868:Hydrolysis; D006882:Hydroxyapatites; D008970:Molecular Weight; D020652:Peptide Elongation Factor 2; D010445:Peptide Elongation Factors / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D010769:Phosphothreonine / Q000378:metabolism; D011494:Protein Kinases / Q000302:isolation & purification / Q000378:metabolism*; D012313:RNA; D011817:Rabbits; D012156:Reticulocytes / Q000032:analysis; D012685:Sepharose
D002147:Calmodulin; D006882:Hydroxyapatites; D020652:Peptide Elongation Factor 2; D010445:Peptide Elongation Factors; D010750:Phosphoproteins; D010769:Phosphothreonine; D012313:RNA; D000255:Adenosine Triphosphate; D012685:Sepharose; D017886:Durapatite; D011494:Protein Kinases; D002118:Calcium