We have obtained two new crystal forms of the Ascaris major sperm protein (MSP) that mediates amoeboid cell motility in nematode sperm, We obtained crystals with C2 symmetry from bacterially expressed alpha-MSP with a = 216.5 Angstrom, b = 38.6 Angstrom, c = 32.5 Angstrom, gamma = 93.1 degrees and also crystals with P2(1) symmetry from native beta-MSP with a = 63.1 Angstrom, b = 91.7 Angstrom, c = 72.5 Angstrom, gamma = 91.3 degrees. A fall native data set has been collected for each crystal form using synchrotron radiation. Both crystal forms diffract to 2 Angstrom and are suitable for high-resolution structural investigation. (C) 1996 Academic Press, Inc.