Structural basis for amoeboid motility in nematode sperm

Cell locomotion in amoeboid nematode sperm is generated by the vectorial assembly and bundling of filaments of the major sperm protein (MSP). MSP filaments are constructed from two helical subfilaments and here we describe the structure of putative MSP subfilament helices determined by X-ray crystallography at 3.3 Angstrom resolution. In addition to establishing the interfaces involved in polymerization, this structural model shows that the MSP helices are constructed from dimers and have no overall polarity, suggesting that it is unlikely that molecular motors play a direct role in the generation of protrusive force in these amoeboid cells.