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MBC in Press, published online ahead of print July 18, 2007
Mol. Biol. Cell 10.1091/mbc.E06-10-0917

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Submitted on October 13, 2006
Revised on July 3, 2007
Accepted on July 5, 2007

Chlamydomonas Outer Arm Dynein Alters Conformation in Response to Ca2+

Miho Sakato,*{dagger} Hitoshi Sakakibara,{ddagger} and Stephen M. King*

*Department of Molecular, Microbial, and Structural Biology, University of Connecticut Health Center, Farmington, CT 06030; {ddagger}Kobe Advanced ICT Research Center, National Institute of Information and Communications Technology, 588-2 Iwaoka, Nishi-ku, Kobe 651-2492, Japan

Monitoring Editor: Erika Holzbaur

We have previously shown that Ca2+ directly activates ATP-sensitive microtubule binding by a Chlamydomonas outer arm dynein subparticle containing the {beta} and {gamma} heavy chains. The {gamma} heavy chain-associated LC4 light chain is a member of the calmodulin family and binds 1-2 Ca2+ with KCa = 3 x 10-5 M in vitro, suggesting it may act as a Ca2+-sensor for outer arm dynein. Here we investigate interactions between the LC4 light chain and {gamma} heavy chain. 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 Ca2+-dependent interaction with the IQ motif domain while remaining tethered to the HC. LC4 also moves into close proximity of the IC IC1 in the presence of Ca2+. The sedimentation profile of the {gamma} heavy chain subunit changed subtly upon Ca2+ 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 Ca2+ addition. We propose that Ca2+-dependent conformational change of LC4 has a direct effect on the stem domain of the {gamma} heavy chain which eventually leads to alterations in mechanochemical interactions between microtubules and the motor domain(s) of the outer dynein arm.

{dagger}Present address: Department of Molecular Biology and Biochemistry, Wesleyan University, Middletown, CT.

Address correspondence to: Stephen M. King (king{at}neuron.uchc.edu)




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 Eukaryot CellHome page
Z. Liu, H. Takazaki, Y. Nakazawa, M. Sakato, T. Yagi, T. Yasunaga, S. M. King, and R. Kamiya
Partially Functional Outer-Arm Dynein in a Novel Chlamydomonas Mutant Expressing a Truncated {gamma} Heavy Chain
Eukaryot. Cell, July 1, 2008; 7(7): 1136 - 1145.
[Abstract] [Full Text] [PDF]


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