A repetitive protein from Trypanosoma brucei which caps the microtubules at the posterior end of the cytoskeleton.

The major structural component of the cyto-architecture of Trypanosoma brucei is a microtubular array which envelopes the entire cell body and which is in close contact with the overlying cell membrane. A cytoskeletal protein has been identified which is associated with the microtubules of this array at their posterior ends exclusively. This protein, Gb4, is coded for by a very large gene which consists of numerous, tandemly linked repeat units of 0.6 kb length. Despite the large size of the gene, and also of the corresponding mRNA, the mature Gb4 protein has a size of only 28 kDa. Gb4 is well conserved between different species of African trypanosomes.