Computer modelling of Tetrahymena axonemes at macromolecular resolution: Interpretation of electron micrographs

A computer-generated model of the structural arrangement of the complete 9+2 ciliary axoneme of Tetrahymena at macromolecular resolution (4 nm) is presented. The model reconciles detailed information about subcomponents from negative-stained, thin-section and freeze-fracture electron micrographs, integrating the images into a consistent three-dimensional picture. This illuminates problems such as the requirement for compaction of dynein to form the arm, difficulties in visualization of the circumferential links, construction of the central sheath, and the comparative periodicities of the inner and outer arms. The model is pragmatic in that it is flexible and easily changed, as new information becomes available. It is also useful in the development of dynamic concepts, such as a spatial description of the dynein cross-bridge cycle, which is illustrated, or relationships between adjacent doublets during sliding and bending.