Functional implications of the unusual amino acid sequence of the regulatory light chain of Acanthamoeba castellanii myosin-II.
We have determined by protein chemistry methods the amino acid sequence of light chain 2 from Acanthamoeba castellanii myosin-II (ALC2). This is the first reported sequence for any protozoan myosin light chain. ALC2 consists of 154 amino acid residues, including a single residue of His and two residues each of Pro and Tyr, and lacks Cys and Trp. The N-terminus is blocked, and if an N-terminal acetyl group is assumed. ALC2 has a calculated molecular weight of 17,657. ALC2 is an acidic protein, with a calculated net charge of -7 at pH 7. The sequence of ALC2 is most similar to those of the calmodulins (identity approximately 35%), followed by myosin regulatory light chains. ALC2 appears to lack the potential N-terminal phosphorylation site and single Ca(2+)-binding site in region I which are characteristic of most myosin regulatory light chains. Instead, ALC2, unlike any other myosin light chain characterized to date, may have a functional Ca(2+)-binding site only in region II, suggesting a novel role of ALC2 in the Ca2+ regulation of the activity of Acanthamoeba myosin-II.
Kobayashi
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Department of Biological Chemistry, School of Medicine, University of Maryland, Baltimore 21201.
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Pollard
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Collins
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D000048:Acanthamoeba / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000378:metabolism; D002147:Calmodulin / Q000378:metabolism; D008969:Molecular Sequence Data; D015879:Myosin Subfragments / Q000378:metabolism; D009218:Myosins / Q000378:metabolism*; D016415:Sequence Alignment
D002135:Calcium-Binding Proteins; D002147:Calmodulin; D015879:Myosin Subfragments; D009218:Myosins; D002118:Calcium