The influence of trace amount of calponin on the smooth muscle myosins in different states.
Calponin (CaP), a thin filament-associated protein, plays an important role in the regulation of smooth muscle contractility. It has been known that CaP inhibits the actin-activated myosin MgATPase activity via binding to F-actin, and stimulates myosin MgATPase activity via binding to myosin. Our recent study revealed a new phenomenon that trace amount of CaP (TAC) could influence the function of different states of myosin. Our data showed that in the absence of actin, CaP, even in the concentration of 0.0001 microM, significantly increased the precipitations of 1 microM unphosphorylated myosin, Ca(2+)-CaM dependently, and independently phosphorylated myosin by MLCK, and stimulated the MgATPase activities of these myosins slightly but significantly. However, no obvious change of precipitation of myosin phosphorylated by PKA was observed, indicating the relative selective effect of TAC. In the presence of actin, myosin, and TAC, the increase of myosin precipitation was abolished, and no obvious changes of actin precipitations and actin-activated myosin MgATPase activities were observed implicating the highly efficiency of TAC on myosin being present in the absence of actin. Although we cannot give conclusive comments to our results, we propose that the high efficiency of TAC-myosin interaction is present in the regulation of the function of myosin when actin is dissociated from myosin, even if CaP/myosin ratio is very low; this high efficient interaction between TAC and myosin can be abolished by actin. However, why and how TAC can possess such a high efficiency to influence myosin and how the physiological significance of the high efficiency of TAC is in regulating the interaction between myosin and actin remain to be investigated.
Yang
Jing-Xian
JX
Department of Pharmacology, Dalian Medical University, Dalian 116027, PR China. xiayang9999@sina.com
Feng
Xiao-Hua
XH
Zhang
Ying
Y
Tang
Ze-Yao
ZY
Lin
Yuan
Y
D000199:Actins / Q000737:chemistry / Q000172:deficiency / Q000378:metabolism; D000818:Animals; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000378:metabolism / Q000494:pharmacology*; D002148:Calmodulin-Binding Proteins / Q000378:metabolism / Q000494:pharmacology; D002498:Centrifugation / Q000379:methods; D011232:Chemical Precipitation; D002645:Chickens; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D008840:Microfilament Proteins; D009130:Muscle, Smooth / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D009219:Myosin-Light-Chain Kinase / Q000378:metabolism; D010766:Phosphorylation; D011485:Protein Binding; D024745:Smooth Muscle Myosins / Q000737:chemistry / Q000378:metabolism*; D000096985:Calponins
D000199:Actins; D017301:Ca(2+) Mg(2+)-ATPase; D002118:Calcium; D002135:Calcium-Binding Proteins; D002148:Calmodulin-Binding Proteins; D017868:Cyclic AMP-Dependent Protein Kinases; D008840:Microfilament Proteins; D009219:Myosin-Light-Chain Kinase; D024745:Smooth Muscle Myosins; D000096985:Calponins