MODELLING THE INNER ROWS OF DYNEIN MOTORS IN THE CILIUM

Helen C. Taylor (1), Michael E.J. Holwill (1,2) and Peter Satir (2)
(1) Physics Department, King's College London, UK
(2) Department of Anatomy and Structural Biology, Albert Einstein College of Medicine, NY, USA

In ciliary movement bends move rhythmically along the organelle. The forces required to bend the cilium are generated by rows of dynein motor molecules which cause doublet microtubules lying lengthwise at the periphery of the ciliary axoneme to slide over each other. Outer rows of these dynein 'arms' control the beat frequency of the cilium while inner rows control the shape of the bends. In previous computer models of the cilium we [2] constructed the inner dynein arms as mirror images of the outer arms. New structural information on Chlamydomonas and other flagella suggests that there are three differing inner arm complexes within a 96 nm axial period of the cilium. Our revised model is consistent with optical diffraction data [2], differential averaging images of Chlamydomonas mutant flagella [1], and freeze-etch and thin-section analyses of eel sperm tails [3]. The model has enabled us to successfully explain various different structural interpretations for the inner arms. Although evidence for conformational changes of these arms is limited, the model has shown that there are a number of constraints on the probable nature of the mechanochemical cycle of each arm. These arise from the requirement of bridging the interdoublet gap whilst avoiding collision with other structures. The study has identified several alternative cycles for one of the inner arms; to distinguish between these alternatives, electron microscopy of axonemal views determined by the modelling procedure are currently being obtained.

[1] Gardner L.C. et al (1994) J. Cell Biol. 127:1311-25.
[2] Sugrue P. et al (1991) J. Cell Science 98:5-16.
[3] Woolley D.M. (1997) J. Cell Science 110:58-94.