Phosphorylation of calmodulin on Tyr99 selectively attenuates the action of calmodulin antagonists on type-I cyclic nucleotide phosphodiesterase activity.
Tyr99 phosphorylation of calmodulin appears to induce a distinct conformational change as is evident from the profound attenuation of the Ca(2+)-induced enhancement of calmodulin's mobility seen during SDS/PAGE. The effect of this conformational change appears to be localized, in that both calmodulin and P-Tyr99-calmodulin show identical dose-dependent activation profiles for stimulation of a physiological effector, type-I (Ca2+/calmodulin-stimulated) cyclic nucleotide phosphodiesterase (PDE) activity and their presence engenders similar dose-dependent PDE activation by Ca2+. In marked contrast with this, with P-Tyr99-calmodulin there were 3-4-fold increases in the IC50 values for inhibition of type-I PDE activity by the calmodulin antagonists TFP and W7, together with increased values for Hill coefficients for inhibition. The polybasic compound poly(L-lysine) potently augmented the action of calmodulin as a PDE activator, causing an approx. 7-fold decrease in the EC50 value for activation of PDE. It is suggested (i) that the Tyr99 phosphorylation of calmodulin, which occurs within a high-affinity Ca(2+)-binding domain, induces a localized conformational change in this peptide which can selectively attenuate the action of calmodulin antagonists on type-I PDE activity while leaving unaffected Ca(2+)-dependent activation, and (ii) that polybasic substances on complexing with calmodulin may serve to enhance the sensitivity of type-I PDE to activation by this regulatory peptide.
Saville
M K
MK
Department of Biochemistry, University of Glasgow, Scotland, U.K.
Houslay
M D
MD
D015105:3',5'-Cyclic-AMP Phosphodiesterases / Q000378:metabolism*; D002147:Calmodulin / Q000037:antagonists & inhibitors / Q000378:metabolism*; D004789:Enzyme Activation; D005260:Female; D006801:Humans; D055504:Insulin Receptor Substrate Proteins; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D011972:Receptor, Insulin / Q000378:metabolism; D014443:Tyrosine / Q000378:metabolism*
D002147:Calmodulin; C526292:IRS1 protein, human; D055504:Insulin Receptor Substrate Proteins; D010750:Phosphoproteins; D014443:Tyrosine; D011972:Receptor, Insulin; D015105:3',5'-Cyclic-AMP Phosphodiesterases