The motile major sperm protein (MSP) of Ascaris suum forms filaments constructed from two helical subfilaments

Journal of Molecular Biology
M StewartT M Roberts


The amoeboid motility nematode sperm is mediated by cytoskeletal filaments composed of major sperm protein (MSP). We have used electron microscopy and image processing to show that MSP filaments are constructed from two subfilament strands which are themselves formed from a helical arrangement of subunits. The subfilaments are based on left-handed helices of pitch 9 nm that then coil along right-handed helical tracks of pitch 22.5 nm to form filaments. The subfilaments appear to be indistinguishable from the helices present in orthorhombic crystals of MSP. Because in filaments the subfilaments are themselves helical, not all subunits are able to participate in protein-protein interactions between different strands. One consequence of this interaction geometry is that the same molecular interactions that function to assemble subfilaments into filaments can also be used to assemble filaments into larger supramolecular assemblies such as the macrofibres formed in vitro and the fibre bundles found in vivo in sperm pseudopods. These results indicate the importance of filament bundling in addition to vectorial filament assembly in amoeboid cell motility.


Mar 21, 1998·Nature Structural Biology·T L BullockM Stewart
Nov 1, 1996·Molecular Reproduction and Development·A Mansir, J L Justine
Nov 21, 2007·Journal of Cellular Biochemistry·Antonio del Castillo-Olivares, Harold E Smith
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May 13, 2008·Trends in Cell Biology·Sima LevNili Dahan
Feb 7, 2001·Science·L Mahadevan, P Matsudaira

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