title: Chlamydomonas outer arm dynein alters conformation in response to Ca2+.
abstract: We have previously shown that Ca(2+) directly activates ATP-sensitive microtubule binding by a Chlamydomonas outer arm dynein subparticle containing the beta and gamma heavy chains (HCs). The gamma HC-associated LC4 light chain is a member of the calmodulin family and binds 1-2 Ca(2+) with K(Ca) = 3 x 10(-5) M in vitro, suggesting it may act as a Ca(2+) sensor for outer arm dynein. Here we investigate interactions between the LC4 light chain and gamma HC. Two IQ consensus motifs for binding calmodulin-like proteins are located within the stem domain of the gamma heavy chain. In vitro experiments indicate that LC4 undergoes a Ca(2+)-dependent interaction with the IQ motif domain while remaining tethered to the HC. LC4 also moves into close proximity of the intermediate chain IC1 in the presence of Ca(2+). The sedimentation profile of the gamma HC subunit changed subtly upon Ca(2+) addition, suggesting that the entire complex had become more compact, and electron microscopy of the isolated gamma subunit revealed a distinct alteration in conformation of the N-terminal stem in response to Ca(2+) addition. We propose that Ca(2+)-dependent conformational change of LC4 has a direct effect on the stem domain of the gamma HC, which eventually leads to alterations in mechanochemical interactions between microtubules and the motor domain(s) of the outer dynein arm.
authors.affiliation: Department of Molecular, Microbial, and Structural Biology, University of Connecticut Health Center, Farmington, CT 06030, USA.
authors.forename: Miho
authors.initials: M
authors.lastname: Sakato
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Sakakibara
authors.forename: Stephen M
authors.initials: SM
authors.lastname: King
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D000906:Antibodies; D002118:Calcium / Q000494:pharmacology*; D002696:Chlamydomonas / Q000378:metabolism*; D003432:Cross-Linking Reagents / Q000494:pharmacology; D003593:Cytoplasm / Q000187:drug effects / Q000378:metabolism; D004398:Dyneins / Q000737:chemistry* / Q000648:ultrastructure; D008969:Molecular Sequence Data; D050505:Mutant Proteins / Q000378:metabolism; D011485:Protein Binding / Q000187:drug effects; D017434:Protein Structure, Tertiary / Q000187:drug effects; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism
chemical_list: D000906:Antibodies; D003432:Cross-Linking Reagents; D050505:Mutant Proteins; D021122:Protein Subunits; D004398:Dyneins; D002118:Calcium