Structure of the small Dictyostelium discoideum myosin light chain MlcB provides insights into MyoB IQ motif recognition.
Dictyostelium discoideum MyoB is a class I myosin involved in the formation and retraction of membrane projections, cortical tension generation, membrane recycling, and phagosome maturation. The MyoB-specific, single-lobe EF-hand light chain MlcB binds the sole IQ motif of MyoB with submicromolar affinity in the absence and presence of Ca(2+). However, the structural features of this novel myosin light chain and its interaction with its cognate IQ motif remain uncharacterized. Here, we describe the NMR-derived solution structure of apoMlcB, which displays a globular four-helix bundle. Helix 1 adopts a unique orientation when compared with the apo states of the EF-hand calcium-binding proteins calmodulin, S100B, and calbindin D9k. NMR-based chemical shift perturbation mapping identified a hydrophobic MyoB IQ binding surface that involves amino acid residues in helices I and IV and the functional N-terminal Ca(2+) binding loop, a site that appears to be maintained when MlcB adopts the holo state. Complementary mutagenesis and binding studies indicated that residues Ile-701, Phe-705, and Trp-708 of the MyoB IQ motif are critical for recognition of MlcB, which together allowed the generation of a structural model of the apoMlcB-MyoB IQ complex. We conclude that the mode of IQ motif recognition by the novel single-lobe MlcB differs considerably from that of stereotypical bilobal light chains such as calmodulin.
From the Department of Biomedical and Molecular Sciences and.
Janine
J
Liburd
From the Department of Biomedical and Molecular Sciences and.
Seth
S
Chitayat
From the Department of Biomedical and Molecular Sciences and.
Scott W
SW
Crawley
the Protein Function Discovery Group, Queen's University, Kingston, Ontario K7L 3N6, Canada.
Kim
K
Munro
From the Department of Biomedical and Molecular Sciences and.
Emily
E
Miller
From the Department of Biomedical and Molecular Sciences and.
Chris M
CM
Denis
From the Department of Biomedical and Molecular Sciences and.
Holly L
HL
Spencer
From the Department of Biomedical and Molecular Sciences and the Protein Function Discovery Group, Queen's University, Kingston, Ontario K7L 3N6, Canada coteg@queensu.ca.
Graham P
GP
Côté
From the Department of Biomedical and Molecular Sciences and the Protein Function Discovery Group, Queen's University, Kingston, Ontario K7L 3N6, Canada steven.smith@queensu.ca.
Steven P
SP
Smith
D000595:Amino Acid Sequence; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism; D004023:Dictyostelium / Q000737:chemistry / Q000378:metabolism*; D020832:EF Hand Motifs; D008969:Molecular Sequence Data; D009154:Mutation; D018994:Myosin Light Chains / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D024501:Nonmuscle Myosin Type IIB / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D015800:Protozoan Proteins / Q000737:chemistry* / Q000378:metabolism
D018994:Myosin Light Chains; D015800:Protozoan Proteins; D024501:Nonmuscle Myosin Type IIB; D002118:Calcium
Calcium-binding Protein; Dictyostelium; Myosin; Protein Structure; Protein-Protein Interaction