Structure of the regulatory domain of scallop myosin at 2 A resolution: implications for regulation

Structure. 1996 Jan 15;4(1):21-32. doi: 10.1016/s0969-2126(96)00006-8.


Background: In contrast to the myosins of vertebrate skeletal muscle, molluscan myosins are regulated molecules whose enzymatic activity is switched on by the direct binding of Ca2+. The head portion (S1) of the molecule consists of a motor domain and a regulatory domain (RD) containing a 'regulatory' and an 'essential' light chain (RLC and ELC, respectively). The structures of scallop myosin RD with bound Ca2+, as well as the S1 fragment of chicken skeletal muscle myosin, have been determined previously to 2.8 A resolution.

Results: We have determined the structure at 2.0 A resolution of scallop myosin RD with bound Ca2+. The unusual coordination at the specific Ca(2+)-binding site in the ELC has now been clarified, as has the structural basis for Mg2+ binding to the RLC. A comparison of the scallop RD structure with that in the chicken S1 structure shows differences in the bending of the two RDs in two different places.

Conclusions: Based on these structural results, a model for regulation is proposed in which the Ca(2+)-bound RD is a rigid structure, and transient flexibility of the Ca(2+)-free RD allows the myosin heads to make stabilizing intramolecular linkage which shut off the motor.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adenosine Triphosphatases / chemistry
  • Animals
  • Binding Sites
  • Calcium / metabolism
  • Chickens / metabolism
  • Computer Graphics
  • Crystallography, X-Ray
  • Magnesium / metabolism
  • Models, Molecular
  • Muscle, Skeletal / chemistry
  • Muscle, Skeletal / metabolism
  • Myosins / chemistry*
  • Protein Structure, Secondary
  • Shellfish


  • Adenosine Triphosphatases
  • Myosins
  • Magnesium
  • Calcium