Characterization and localization of a flagellar-specific membrane glycoprotein in Euglena

Purified flagella from Euglena yield a unique high molecular weight glycoprotein when treated with low concentrations of nonionic detergents. This glycoprotein termed "xyloglycorien" cannot be extracted from other regions of the cell, although a minor component that coextracts with xyloglycorien does have a counterpart in deflagellated cell bodies. Xyloglycorien is tentatively identified with a flagellar surface fuzzy layer that appears in negatively stained membrane vesicles of untreated flagella but not in similar vesicles after Nonidet P-40 extraction. The localization of xyloglycorien is further confirmed to be membrane associated by reciprocal extraction experiments using 12.5 mM lithium diiodosalicylate (LIS), which does not appreciably extract xyloglycorien, visibly solubilize membranes, or remove the fuzzy layer. Rabbit antibodies directed against the two major flagellar glycoproteins (xyloglycorien and mastigonemes) to some extent cross react, which may in part be caused by the large percentage of xylose found by thin-layer chromatography (TLC) analysis to be characteristic of both antigens. However, adsorption of anti-xyloglycorien sera with intact mastigonemes produced antibodies responding only to xyloglycorien, and vice versa, indicating the nonidentity of the two antigens. Antibodies or fragments of these antibodies used in immunofluorescence assays demonstrated that xyloglycorien is confined to the flagellum and possibly the adjacent reservoir and gullet. Binding could not be detected on the cell surface. The sum of these experiments suggests that, in addition to mastigonemes, at least one major membrane glycoprotein in Euglena is restricted to the flagellar domain and is not inserted into the contiguous cell surface region.