Purification, Visualization and Characterization of the Sexual Agglutinins of the Green Alga Chlamydomonas moewusii yapensis

SUMMARY: Purification of the sexual agglutinins of both mating types of Chlamydomonas moewusii yapensis(= C. moewusii syngen II) was achieved by a three-step procedure. Electron microscopy showed both agglutinins to be long, linear molecules. The mt+ agglutinin was a rigid molecule with one bulbous end and an average length of 251 nm. The mt-agglutinin was longer (average length 349 nm), had a more flexible conformation and lacked a bulbous end. The Mr was estimated to be 1·0 × 106 for the mt+ and 1·2 × 106 for the mt- agglutinin. The mt- agglutinin had a very high content of hydroxyproline (41%) and serine (14%); the mt+ agglutinin had a high content of glycine, serine and hydroxyproline (18, 16 and 12%, respectively). The main sugars in the agglutinins of both mating types were arabinose and galactose. The carbohydrate portion represented about 40% of the Mr in both agglutinins. The biological activity of both agglutinins could be destroyed by periodate treatment (although their sensitivities differed), indicating the involvement of carbohydrate residues. A differential susceptibility for exoglycosidases was observed: enzymic removal of terminal glucose residues abolished the biological activity of the mt+ agglutinin only, while removal of mannose residues selectively inactivated the mt- agglutinin. The similarities in form and composition of the agglutinins of several Chlamydomonas species suggest that these recognition molecules have a common ancestry, and that the species barriers are at least partially dependent on differences in the carbohydrate side-chains.