Structure-Function Relationships in Smooth Muscle Myosin Light Chain Kinase

  • Masaaki Ito
  • Vince GuerrieroJr.
  • David J. Hartshorne
Part of the Advances in Experimental Medicine and Biology book series (AEMB, volume 304)


Regulation of the contractile apparatus in vertebrate smooth muscle is thought to involve the phosphorylation-dephosphorylation of the two 20,000-dalton light chains of myosin (Hartshorne, 1987). It has been known for many years that contraction in smooth muscle, as in skeletal muscle, is determined by the concentration of intracellular Ca2+. Contractile activity is coupled to the Ca2+ transients via the formation of the Ca2+-calmodulin (CaM) complex and subsequent activation of the CaM-dependent enzyme, myosin light chain kinase (MLCK). Phosphorylation of the myosin light chain increases the actin-activated ATPase activity of myosin and this event is thought to be reflected, under physiological conditions, by an increased rate of cross-bridge cycling and the development of tension. As long as the intracellular Ca2+ concentration remains above the threshold determined by the affinity of Ca2+ binding to the Ca2+-CaM-MLCK complex (i.e. ∼ 0.5 μM) myosin remains phosphorylated and contraction persists. Reduction in the Ca2+ level leads to a commensurate decrease in kinase activity and varying extents of myosin dephosphorylation. It is assumed (in the absence of conflicting data) that the myosin phosphatase is unregulated and dephosphorylation occurs at the same rate both in the presence and absence of Ca2+. However, the identity of the phosphatase involved in myosin dephosphorylation has not been established and one of the intriguing questions to be answered is whether phosphatase activity is regulated in vivo? Thus, by decreasing the MLCK activity the balance of phosphorylation to dephosphorylation is altered. In the simplest scenario the role of myosin phosphorylation is to initiate contraction and dephosphorylation leads to relaxation. While this simple relationship is not obvious under physiological conditions, and several papers in this volume attest to the complexity of the situation, it is clear that two key regulatory enzymes in smooth muscle are MLCK and myosin phosphatase.


Myosin Light Chain Kinase Inhibitory Domain Inhibitory Sequence Myosin Phosphatase Myosin Light Chain Kinase Activity 
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  1. Dabrowska, R., Sherry, J. M. F., Aromatorio, D. K., and Hartshorne, D. J., 1978, Modulator protein as a component of the myosin light chain kinase from chicken gizzard, Biochemistry, 17: 253.PubMedCrossRefGoogle Scholar
  2. Edelman, A. M., Takio, K., Blumenthal, D. K., Hansen, R. S., Walsh, K. A., Titani, K., and Krebs, E. G., 1985, Characterization of the calmodulin-binding and catalytic domains in skeletal muscle myosin light chain kinase, J. Biol Chem., 260: 11275.PubMedGoogle Scholar
  3. Guerriero Jr., V., Russo, M. A., Olson, N. J., Putkey, J. A., and Means, A. R., 1986, Domain organization of chicken gizzard myosin light chain kinase deduced from a cloned cDNA, Biochemistry, 25: 372.CrossRefGoogle Scholar
  4. Hanley, R. M., Means, A. R., Ono, T., Kemp, B. E., Burgin, K. E., Waxham, N., and Kelly, P. T., 1987, Functional analysis of a complementary DNA for the 50-kilodalton subunit of calmodulin kinase II, Science, 237: 293.PubMedCrossRefGoogle Scholar
  5. Hartshorne, D. J., 1987, Biochemistry of the contractile process in smooth muscle, in: “Physiology of the Gastrointestinal tract”, L. R. Johnson, ed., Raven Press, New York, p. 423.Google Scholar
  6. House, C. and Kemp, B. E., 1987, Protein kinase C contains a pseudosubstrate prototype in its regulatory domain, Science, 238: 1726.PubMedCrossRefGoogle Scholar
  7. Ikebe, M., Maruta, S., and Reardon, S., 1989, Location of the inhibitory region of smooth muscle myosin light chain kinase, J. Biol. Chem., 264: 6967.PubMedGoogle Scholar
  8. Ikebe, M., Stepinska, M., Kemp, B. E., Means, A. R., and Hartshorne, D. J., 1987, Proteolysis of smooth muscle myosin light chain kinase. Formation of inactive and calmodulin-independent fragments, J. Biol. Chem., 260: 13828.Google Scholar
  9. Ito, M., Dabrowska, R., Guerriero Jr., V., and Hartshorne, D. J., 1989, Identification in turkey gizzard of an acidic protein related to the C-terminal portion of smooth muscle myosin light chain kinase, J. itBiol. Chem., 264: 13971.Google Scholar
  10. Ito, M., Hartshorne, D. J., Pearson, R., and Kemp, B. E., 1989, Proteolysis of smooth muscle myosin light chain kinase, Biophys. J., 55: 494a.Google Scholar
  11. Kemp, B. E., Pearson, R. B., Guerriero Jr., V., Bagchi, I. C., and Means, A. R., 1987, The calmodulin binding domain of chicken smooth muscle myosin light chain kinase contains a pseudosubstrate sequence, J. Biol. Chem., 262: 2542.PubMedGoogle Scholar
  12. Lukas, T. J., Burgess, W. H., Prendergast, F. G., Lau, W., and Watterson, D. M., 1986, Calmodulin binding domains: Characterization of a phosphorylation and calmodulin binding site from myosin light chain kinase, Biochemistry, 25: 1458.PubMedCrossRefGoogle Scholar
  13. Mayr, G. W. and Heilmeyer Jr., L. M. G., 1983, Skeletal muscle myosin light chain kinase. a refined structural model, FEBS Lett., 157: 225.PubMedCrossRefGoogle Scholar
  14. Olson, N. J., Pearson, R. B., Needleman, D. S., Hurwitz, M. Y., Kemp, B. E., and Means, A. R., 1990, Regulatory and structural motifs of chicken gizzard myosin light chain kinase, Proc. Nat’l. Acad. Sci. U.S.A., 87: 2284.CrossRefGoogle Scholar
  15. Payne, M. E., Fong, Y.-L., Ono, T., Colbran, R.-J., Kemp, B. E., Soderling, T. R., and Means, A. R., 1988, Calcium/calmodulin-dependent protein kinase II. Characterization of distinct calmodulin binding and inhibitory domains, J. Biol. Chem., 263: 7190.PubMedGoogle Scholar
  16. Roush, C. L., Kennelly, P. J., Glaccum, M. B., Helfman, D. M., Scott, J. D., and Krebs, E. G., 1988, Isolation of the cDNA encoding rat skeletal muscle myosin light chain kinase. sequence and tissue distribution, J. Biol. Chem., 263: 10510.PubMedGoogle Scholar
  17. Russo, M. A., Guerriero Jr., V., and Means, A. R., 1987, Hormonal regulation of a 2-7 kb mRNA that shares a common domain with myosin light chain kinase in the chicken oviduct, Mol. Endocrinol., 1: 60.PubMedCrossRefGoogle Scholar
  18. Scholey, J. M., Taylor, K. A., and Kendrick-Jones, J., 1980, Regulation of non-muscle myosin assembly by calmodulin-dependent light chain kinase, Nature, 287: 233.PubMedCrossRefGoogle Scholar
  19. Studier, W. S., Rosenberg, A. H., and Dunn, J. J., 1990, Use of T7 RNA polymerase to direct the expression of cloned genes, Methods Enzymol., 185: 60.PubMedCrossRefGoogle Scholar
  20. Suzuki, H., Onishi, H., Takahashi, K., and Watanabe, S., 1978, Structure and function of chicken gizzard myosin, J. Biochem., 84: 1529.PubMedGoogle Scholar
  21. Takio, K., Blumenthal, D. K., Walsh, K. A., Titani, K., and Krebs, E. G., 1986, Amino acid sequence of rabbit skeletal muscle myosin light chain kinase, Biochemistry, 25: 8049.PubMedCrossRefGoogle Scholar
  22. Taylor, S. S., 1989, cAMP-dependent protein kinase. Model for an enzyme family, J. Biol. Chem., 264: 8443.PubMedGoogle Scholar
  23. Yazawa, M., Kuwayama, H., and Yagi, K., 1978, Modulator protein as a Ca2+-dependent activator of rabbit skeletal myosin light chain kinase, J. Biochem., 84: 1253.PubMedGoogle Scholar

Copyright information

© Plenum Press, New York 1991

Authors and Affiliations

  • Masaaki Ito
    • 2
  • Vince GuerrieroJr.
    • 1
  • David J. Hartshorne
    • 1
  1. 1.Muscle Biology Group Department of Animal SciencesThe University of ArizonaTucsonUSA
  2. 2.The First Medical ClinicMie University HospitalTsu-City, MieJapan

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