Essential for normal male fertility and for progressive motility of spermatozoa. Interacts with HYDIN. Highly expressed in the testis (at protein level) (PubMed:32072696). Weakly expressed in the brain, thymus, lung and heart (PubMed:32072696). Mice exhibit impaired sperm motility and male subfertility and flagella show an asymmetric waveform pattern, which leads to a circular motion of spermatozoa. Belongs to the TRAFAC class myosin-kinesin ATPase superfamily. Kinesin family.