title: Role of essential light chain EF hand domains in calcium binding and regulation of scallop myosin.
abstract: The specific Ca2+ binding site that triggers contraction of molluscan muscle requires the presence of an essential light chain (ELC) from a Ca2+ binding myosin. Of the four EF hand-like domains in molluscan ELCs, only domain III has an amino acid sequence predicted to be capable of binding Ca2+. In this report, we have used mutant ELCs to locate the Ca2+ binding site in scallop myosin and to probe the role of the ELC in regulation. Point mutations in domain III of scallop ELC have no effect on Ca2+ binding. Interestingly, scallop and rat cardiac ELC chimeras support Ca2+ binding only if domain I is scallop. These results are nevertheless in agreement with structural studies on a proteolytic fragment of scallop myosin, the regulatory domain. Furthermore, Ca2+ sensitivity of the scallop myosin ATPase requires scallop ELC domain I: ELCs containing cardiac domain I convert scallop myosin to an unregulated molecule whose activity is no longer repressed in the absence of Ca2+. Despite its unusual EF hand domain sequence, our data indicate that the unique and required contribution of molluscan ELCs to Ca2+ binding and regulation of molluscan myosins resides exclusively in domain I.
authors.affiliation: Brandeis University, Department of Biology, Waltham, MA 02254-9110, USA.
authors.forename: S
authors.initials: S
authors.lastname: Fromherz
authors.forename: A G
authors.initials: AG
authors.lastname: Szent-Györgyi
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism*; D003001:Cloning, Molecular; D016384:Consensus Sequence; D006706:Homeostasis; D008969:Molecular Sequence Data; D008974:Mollusca; D016297:Mutagenesis, Site-Directed; D009206:Myocardium / Q000378:metabolism; D009218:Myosins / Q000096:biosynthesis / Q000737:chemistry* / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D011485:Protein Binding; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism; D017386:Sequence Homology, Amino Acid
chemical_list: D011994:Recombinant Proteins; D009218:Myosins; D002118:Calcium