The Trypanosoma brucei autoantigen I/6 is an internally repetitive cytoskeletal protein

Self-reactive host antibodies were shown earlier to exhibit strong and specific cross-reactivity to a particular trypanosomal antigen, protein I/6. The current study presents the molecular characterization of protein I/6. The major structural component of the cell body cytoskeleton of Trypanosoma brucei is a cagelike array of tightly connected microtubules which is in close contact to the overlaying cell membrane. Many of the unususal properties of the cytoskeleton of trypanosomes are due to the proteins associated with these microtubules. Protein I/6 was now shown to be a microtubule-associated protein, and it may be involved in crosslinking microtubules. Protein I/6 is coded for by a single gene, representing an exception rather than the rule for trypanosomal gene organization. From this single gene, two distinct mRNAs are generated through differential splicing. They differ in their polyadenylation sites, but both code for an identical polypeptide sequence of 33 kDa. Protein I/6 contains a non-functional EF-hand calcium binding domain and a domain of six tandemly arranged repeat units of eight amino acids length.