Dynein

It is a very large protein (1000-2000  kDa)which consisting  of one, two or three heads based  on the source. Such as the heads of myosin and the heads of dynein form cross-bridges, in this case having the B subfibers, and possess ATPase activity. Binding of ATP to dynein causes it to dissociate from the B subfiber.  The dynein binds again with the B subfiber on hydrolysis of the ATP to ADP and Pi, having the subsequent release of the Pi and ADP (a cycle very same to that which take place with the binding of the S1 heads of myosin to ATP). This particular ATPase  cycle leads to the movement  of the cilium as the outer doublets of the axoneme slide past each other. The force between adjacent doublets is generated by the dynein

                                                   Cross-sectional diagram of a cilium.

cross-bridges.  Therefore, the dynein arms on subfiber  A of one doublet  walk along subfiber B of the adjacent doublet. Unlike in muscle,  in a cilium  where the actin and myosin filaments  slide past each other the radial  spokes  resist  the sliding motion,  which instead of it  converted  into a local bending. The extremely extensible protein named nexin, keeps adjacent doublets together during this process.

A  defect  or  absence  in  any  one  of  the  proteins  within  the  axoneme  (for example :  nexin, dynein etc.)  results in cilia  that  are  immotile,  so called as immotile-cilia syndrome.  Patients who  suffering from  this  disease due to the cilia have  chronic  pulmonary  disorders in the respiratory tract being unable to sweep out bacteria and other foreign particles. As well males with this genetic defect are infertile because due to flagella inactivity their sperm are unable to move.