title: Three outer arm dynein heavy chains of Chlamydomonas reinhardtii operate in a coordinated fashion both in vitro and in vivo.
abstract: Outer arm dynein (OAD) in cilia and flagella contains two to three nonidentical heavy chains (HCs) that possess motor activity. In Chlamydomonas, flagellar OAD contains three HCs, alpha-, beta-, and gamma-HCs, each appearing to have a distinct role. To determine the precise molecular mechanism of their function, cross-sectional electron micrographs of wild-type and single HC-disruption mutants were compared and statistically analyzed. While the alpha-HC mutant displayed an OAD of lower density, which was attributed to a lack of alpha-HC, the OAD of beta- and gamma-HC mutants not only lacked the corresponding HC, but was also significantly affected in its structure, particularly with respect to the localization of alpha-HC. The lack of beta-HC induced mislocalization of alpha-HC, while a disruption of the gamma-HC gene resulted in the synchronized movement of alpha-HC and beta-HC in the manners for stacking. Interestingly, using cryo-electron microscopy, purified OADs were typically observed consisting of two stacked heads and an independent single head, which presumably corresponded to gamma-HC. This conformation is different from previous reports in which the three HCs displayed a stacked form in flagella observed by cryo-electron tomography and a bouquet structure on mica in deep-etch replica images. These results suggest that gamma-HC supports the tight stacking arrangement of inter or intra alpha-/beta-HC to facilitate the proper functioning of OAD.
authors.affiliation: Department of Bioscience and Bioinformatics, Kyushu Institute of Technology, Iizuka, Fukuoka, Japan.
authors.forename: Hiroko
authors.initials: H
authors.lastname: Takazaki
authors.forename: Zhongmei
authors.initials: Z
authors.lastname: Liu
authors.forename: Mingyue
authors.initials: M
authors.lastname: Jin
authors.forename: Ritsu
authors.initials: R
authors.lastname: Kamiya
authors.forename: Takuo
authors.initials: T
authors.lastname: Yasunaga
mesh_terms: D054468:Axoneme / Q000648:ultrastructure; D016825:Chlamydomonas reinhardtii / Q000378:metabolism* / Q000648:ultrastructure; D002851:Chromatography, High Pressure Liquid; D020285:Cryoelectron Microscopy; D004398:Dyneins / Q000302:isolation & purification / Q000378:metabolism* / Q000648:ultrastructure; D008954:Models, Biological; D009154:Mutation / Q000235:genetics; D010940:Plant Proteins / Q000302:isolation & purification / Q000378:metabolism* / Q000648:ultrastructure
chemical_list: D010940:Plant Proteins; D004398:Dyneins