Chemical modification of the sole histidine residue of smooth muscle caldesmon.
Caldesmon was stoichiometrically N-carbethoxylated specifically at the only histidine residue (His-610) with diethylpyrocarbonate. Carbethoxylation of a 1:1 molar complex of caldesmon and calmodulin in the presence of Ca2+ resulted in the stoichiometric N-carbethoxylation of His-610 of caldesmon and His-107 of calmodulin. Carbethoxy-caldesmon, like the unmodified protein, bound to immobilized calmodulin (in the presence of Ca2+) and to immobilized tropomyosin (at low ionic strength). The affinity of F-actin for carbethoxy-caldesmon (Kd = 1.29 x 10(-6)M) was similar to that for unmodified caldesmon (Kd = 0.88 x 10(-6)M), and the modified protein was as effective as control caldesmon in the inhibition of the actin-activated MgATPase of skeletal muscle myosin. We conclude that the predicted basic amphiphilic alpha-helical sequence (Arg-593-His-610) does not represent the calmodulin-binding site of caldesmon. Furthermore, His-610 does not play a major role in the interaction of caldesmon with F-actin or tropomyosin.
Bonet-Kerrache
A A
AA
Department of Medical Biochemistry, University of Calgary, Alberta, Canada.
Walsh
M P
MP
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001921:Brain / Q000378:metabolism; D002147:Calmodulin / Q000378:metabolism; D002148:Calmodulin-Binding Proteins / Q000378:metabolism*; D002417:Cattle; D002645:Chickens; D004047:Diethyl Pyrocarbonate / Q000494:pharmacology*; D005895:Gizzard, Avian; D006639:Histidine; D007700:Kinetics; D009130:Muscle, Smooth / Q000378:metabolism
D002147:Calmodulin; D002148:Calmodulin-Binding Proteins; D006639:Histidine; D000255:Adenosine Triphosphate; D004047:Diethyl Pyrocarbonate