Evidence for a Mr 88,000 glycoprotein with a transmembrane association to a unique flagellum attachment region in Trypanosoma brucei.

We have examined the relationship of externally accessible proteins associated with the internal cytoskeleton of procyclic Trypanosoma brucei. Two approaches were taken. First, externally disposed glycoproteins were identified with lectins and examined for their persistence and location in isolated cytoskeletons. Second, proteins containing tyrosine residues available for chemical modification on the outer surface were identified in isolated cytoskeletons and probed for glycosylation. The procyclic form of T. brucei that was employed does not express the variable surface glycoprotein. The lectin concanavalin A (ConA) bound to the outer surface of T. brucei in two discrete locations; one a narrow line close to the flagellum attachment zone on the cell body, the other at the distal tip of the flagellum itself. Of these, only the cell body labelling was detected when isolated cytoskeletons were probed with fluorescein isothiocyanate-labelled ConA. When cytoskeletons were prepared from cells labelled with gold-conjugated ConA, a narrow line of label was detected parallel to the flagellum attachment zone but was distinct from it. Only one cytoskeletal protein, of Mr 88,000, could be labelled at the cell surface by the 125I/iodogen procedure. This protein could be precipitated from SDS-solubilized cytoskeletons with ConA-agarose. These data indicate the existence of a previously undetected cytoskeletal structure, situated in the cell body, close to the point of flagellum attachment, which has a transmembrane association with an external Mr 88,000 glycoprotein.