ACTIVATION BY AUTOPHOSPHORYLATION OR CGMP BINDING PRODUCES A SIMILAR APPARENT CONFORMATIONAL CHANGE IN CGMP-DEPENDENT PROTEIN-KINASE

Binding of cyclic nucleotide to or autophosphorylation of cGMP-depende nt protein kinase (PKG) activates this kinase, but the molecular mecha nism of activation for either process is unknown. Activation of PKG by cGMP binding produces a conformational change in the enzyme (Chu, D.- M., Corbin, J. D., Grimes, K. A., and Francis, S. H. (1997) J. Biol. C hem. 272, 31922-31928; Zhao, J., Trewhella, J., Corbin, J., Francis, S ., Mitchell, R., Brushia, R., and Walsh, D. (1997) J. Biol. Chem. 272, 39129-31936). In the present studies, activation of type Ip PKG by ei ther autophosphorylation or cGMP-binding alone causes (i) an electrone gative charge shift on ion exchange chromatography, (ii) a similar inc rease (similar to 3.5 Pi) in the Stokes radius as determined by gel fi ltration chromatography, and (iii) a similar decrease in the mobility of the enzyme on native gel electrophoresis. Consistent with these res ults, cGMP binding increases the rate of phosphoprotein phosphatase-l catalyzed dephosphorylation of PKG which is autophosphorylated only at Ser-63 (not activated); however, dephosphorylation of PKC: that is hi ghly autophosphorylated (activated) is not stimulated by cGMP. The com bined results suggest that activation of PKG by either autophosphoryla tion or cGMP binding alone produces a similar apparent elongation of t he enzyme, implying that either process activates the enzyme by a simi lar molecular mechanism.