[1] The MSP has two main functions in the reproduction of the helminthes: i) as cytosolic component it is responsible for the crawling movement of the mature sperm (without flagellum), and ii) once released, it acts as hormone on the female germ cells, where it triggers oocyte maturation and stimulates the oviduct wall to contract to bring the oocytes into position for fertilization.

Molecular structures of MSP from Ascaris suum and Caenorhabditis elegans have been determined by X-ray crystallography[3] and NMR spectroscopy.

The unique strand switches between the sheets result from two distinct kinks at cis-proline residues 13 and 57 in A. suum protein.

It was suggested that ATP activates either membrane-bound MSP filament end-tracking proteins or their soluble cofactors.

Locomotion in nematodes occurs by localized extension of the leading edge of the pseudopod, attachment of the cytoskeleton to the substrate, and retraction of the cell.

Assembly of MSP filaments at the leading edge together with disassembly at the base of the pseudopod results in a treadmilling motion, which corresponds to the crawling locomotion of nematode sperm.

[11] Degradation of the MSP filaments results in a traction force at the base of the pseudopod, which in turn pulls the cytoskeleton forward.

Despite only 11% of sequence similarity, MSP and the N-terminus of the bacterial P-pilus associated chaperonin PapD share a high structural and topological homology in their β sheet regions.

Both MSP and PapD can be classified to the s-type immunoglobulin fold proteins, characterized by the above-mentioned unique strand switching.