title: Structure and properties of casein kinase-2 from Saccharomyces cerevisiae. A comparison with the liver enzyme.
abstract: A type-2 casein kinase (YCK-2), lacking the 25-kDa autophosphorylatable beta subunit characteristic of animal casein kinases-2, has been obtained in a nearly pure form from Saccharomyces cerevisiae and was compared with liver casein kinase-2 (LCK-2). A 22-kDa phosphorylatable protein, copurifying with YCK-2, can be removed by ultracentrifugation at low ionic strength and is shown by several criteria to be unrelated to the beta subunit of LCK-2. The native Mr of YCK-2, deprived of the 22-kDa phosphoprotein, is about 150 000. Limited proteolysis experiments show that YCK-2 included 37-kDa catalytic subunits, which can be converted into still active 35-kDa proteolytic derivatives. These data are consistent with a homotetrameric quaternary structure as opposed to the heterotetrameric subunit composition alpha 2 beta 2 of LCK-2 and other animal casein kinases-2. Although many properties of YCK-2 and LCK-2, including substrate specificity, inhibition by heparin, polyglutamic acid and quercetin and stimulation by polyamines, are similar; their stability under denaturing and dissociating conditions and their response to polybasic peptides are quite different. In particular YCK-2 is more readily denatured than LCK-2 by heating and exposure to urea, sodium dodecylsulphate and deoxycholate while its activity is inhibited by 100-150 mM NaCl, which conversely stimulates LCK-2 activity 2-3-fold. The Km value of the synthetic peptide substrate Ser-(Glu)5 for YCK-2 is not significantly changed by the addition of polylysine. On the contrary the Km value of the same peptide substrate for LCK-2 decreases approximately tenfold upon addition of polylysine, which also prevents the fast autophosphorylation of the kinase at its beta subunit. These data suggest that the beta subunit of animal CK-2 may play a role in determining both the stability of the enzyme and its regulation and that, consequently, the different properties of YCK-2 may be at least in part accounted for by its lack of beta subunits.
mesh_terms: D000818:Animals; D047388:Casein Kinases; D002499:Centrifugation, Density Gradient; D055598:Chemical Phenomena; D002621:Chemistry; D008099:Liver / Q000201:enzymology*; D010446:Peptide Fragments / Q000032:analysis; D010766:Phosphorylation; D011489:Protein Denaturation; D047428:Protein Kinase Inhibitors; D011494:Protein Kinases / Q000378:metabolism*; D051381:Rats; D012441:Saccharomyces cerevisiae / Q000201:enzymology*; D013045:Species Specificity
chemical_list: D010446:Peptide Fragments; D047428:Protein Kinase Inhibitors; D011494:Protein Kinases; D047388:Casein Kinases