The mechanical behavior of doublet microtubules simulated by helical models

The structural and mechanical properties of the helix‐shaped isolated doublet microtubules described by Costello [Biol. Bull. 145:279–291, 1973], Zobel [J. Cell Biol. 59:573–94, 1973], and Miki‐Noumura and Kamiya [Exp. Cell Res. 97:451–53, 1976, J. Cell Biol 81:355–60, 1979] are simulated by a left‐handed superhelix model that consists of two intertwined springlike helices with a slight difference in their pitches. It is shown by combinations of two and more superhelices of this kind that the straight shape of the doublets in the axoneme is the consequence of a position‐dependent mechanical coil‐coil interaction between interconnected doublets whose curvatures bend against one another. A counterclockwise torsion changes the sense of the superhelix from the left‐handed form with a smaller pitch (L 2 ) to the right‐handed form with a larger pitch (R 3 ). The coil‐coil interaction of L helices with R helices results in uniplanar, meanderlike shapes or in flattened helices. The one‐sided distribution of L and R doublets as described for sperm axonemes by Costello [Biol. Bull. 145:279–91, 1973] may therefore be responsible for the uniplanar. meanderlike shape of these flagella.