Phosphorylation of proteins in Clostridium thermohydrosulfuricum

Abstract

Cell extracts of the thermophile Clostridium thermohydrosulfuricum catalyzed the phosphorylation by [gamma-32P]ATP of several endogenous proteins with Mrs between 13,000 and 100,000. Serine and tyrosine were the main acceptors. Distinct substrate proteins were found in the soluble (e.g., proteins p66, p63, and p53 of Mrs 66,000, 63,000, and 53,000, respectively) and particulate (p76 and p30) fractions, both of which contained protein kinase and phosphatase activity. The soluble fraction suppressed the phosphorylation of particulate proteins and contained a protein kinase inhibitor. Phosphorylation of p53 was promoted by 10 microM fructose 1,6-bisphosphate or glucose 1,6-bisphosphate and suppressed by hexose monophosphates, whereas p30 and p13 were suppressed by 5 microM brain (but not spinach) calmodulin. Polyamines, including the "odd" polyamines characteristic of thermophiles, modulated the labeling of most of the phosphoproteins. Apart from p66, all the proteins labeled in vitro were also rapidly labeled in intact cells by 32Pi. Several proteins strongly labeled in vivo were labeled slowly or not at all in vitro.