抄録
Myosin light chain kinase (MLCK) is a multifunctional regulatory protein of smooth muscle contraction. The well-established mode for its regulation is to phosphorylate the 20kDa myosin light chain (MLC20) to activate myosin ATPase activity. MLCK exhibits myosin-binding activity in addition to this kinase activity. The myosin-binding activity also stimulates myosin ATPase activity without phosphorylating MLC20. In order to study this non-kinase activity of MLCK and its active site. We engineered two MLCK fragments, one contained the myosin-binding domain but devoid of a catalytic domain and another further deleted a calmodulin (CaM) domain. The former fragment stimulated myosin ATPase activity by Vmax= 5.53 ± 0.63- fold with Km = 4.22 ± 0.586μM (n = 4). Similar stimulation figures were obtained by measuring the ATPase activity of HMM and S1. We failed to observe the stimulation with the latter fragment. Similar stimulating effect were obtained by measuring the ATPase activity of phosphorylated myosin, HMM and S1. Binding of the fragment to both HMM and S1 was also verified, indicating that the fragment exerts stimulation through the myosin heads. We conclude that the non-kinase stimulation of MLCK are involved in the mode for activation of myosin. The CaM domain is one of the active site for non-kinase activity of MLCK fragment. [J Physiol Sci. 2006;56 Suppl:S68]
