Summary

The flagellar surface of Chlamydomonas moewu-sii is a dynamic structure involved in several adhesive and motile events. In this report, we describe for the first time the flagellar membrane components of vegetative C. moewusii. A glyco-protein (or pair of glycoproteins) with an appar-ent molecular weight of 240xlO3 is the dominant flagellar protein (other than the tubulins) in this species of Chlamydomonas. Both a rabbit poly-clonal antibody (designated P-19) and the lectin concanavalin A recognize this 240K (K = 103Mr) glycoprotein on nitrocellulose transblots of flagel-lar proteins. Fluorescence microscopic studies using these same two probes suggest that the 240K glycoprotein is exposed at the flagellar surface. Direct evidence that the 240K glycoprotein is exposed at the flagellar surface is provided by vectorial labelling with a JV-hydroxysuccinamide-derivitized biotin reagent (NHS-LC-biotin). Non-ionic detergent extraction of isolated flagella fails to solubilize most of the 240K glycoprotein, although it completely removes the flagellar membranes as demonstrated by transmission electron microscopy. Furthermore, immuno-fluorescence microscopy of isolated axonemes demonstrates that both P-19-defined epitopes and surface-biotinylated proteins continue to be as-sociated with the axoneme structure after deter-gent treatment. These observations demonstrate that the 240K flagellar protein is a glycoprotein that is both exposed at the flagellar surface and tightly coupled to the underlying cytoskeleton (axoneme). Because of its cell surface orientation and axonemal linkage, it is likely that the 240K glycoprotein plays an important role in the ad-hesive and/or motile phenomena exhibited by the C. moewusii flagellar surface