The F1-ATPase from Trypanosoma brucei is elaborated by three copies of an additional p18-subunit

The F-ATPases (also called the F1Fo-ATPases or ATP synthases) are multi- subunit membrane-bound molecular machines that produce ATP in bacteria and in eukaryotic mitochondria and chloroplasts. The structures and enzymic mechanisms of their F-1-catalytic domains are highly conserved in all species investigated hitherto. However, there is evidence that the F-ATPases from the group of protozoa known as Euglenozoa have novel features. Therefore, we have isolated pure and active F-1-ATPase from the euglenozoan parasite, Trypanosoma brucei, and characterized it. All of the usual eukaryotic subunits (alpha, beta, gamma, delta, and epsilon) were present in the enzyme, and, in addition, two unique features were detected. First, each of the three a-subunits in the F-1-domain has been cleaved by proteolysis in vivo at two sites eight residues apart, producing two assembled fragments. Second, the T. brucei F-1-ATPase has an additional subunit, called p18, present in three copies per complex. Suppression of expression of p18 affected in vitro growth of both the insect and infectious mammalian forms of T. brucei. It also reduced the levels of monomeric and multimeric F-ATPase complexes and diminished the in vivo hydrolytic activity of the enzyme significantly. These observations imply that p18 plays a role in the assembly of the F-1 domain. These unique features of the F-1-ATPase extend the list of special characteristics of the F-ATPase from T. brucei, and also, demonstrate that the architecture of the F-1-ATPase complex is not strictly conserved in eukaryotes.