GPEET PROCYCLIN IS THE MAJOR SURFACE PROTEIN OF PROCYCLIC CULTURE FORMS OF TRYPANOSOMA-BRUCEI-BRUCEI STRAIN-427

The surface of Trypanosoma brucei brucei insect forms is covered by an invariant protein coat consisting of procyclins. There are six or sev en procyclin genes that encode unusual proteins with extensive tandem repeat units of glutamic acid (E) and proline (P) (referred to as EP r epeats), and two genes that encode proteins with internal pentapeptide (GPEET) repeats. Although the EP forms of procyclins have been isolat ed and characterized by several laboratories, evidence for GPEET procy clin has largely been confined to the expression of its mRNA. To chara cterize GPEET procyclin further, we isolated the protein from T. b. br ucei strain 427. We found that label from [SH]myristic acid and [H-3]e thanolamine was incorporated into GPEET procyclin and we demonstrated the protein's covalent modification with a glycosylphosphatidylinosito l anchor. The major form of GPEET procyclin showed an apparent molecul ar mass of 22-32 kDa, was susceptible to proteolytic treatment and was found to be phosphorylated. Surprisingly, our results show that GPEET procyclin represents the major form of procyclin in T. b. brucei 427 culture forms and that the ratio of EP to GPEET procyclin can vary con siderably between different cell lines.