ARL1 has an essential role in Trypanosoma brucei

Myristoyl-CoA protein:NMT (N-myristoyl transferase) catalyses the N-myristoylation of cellular proteins with a range of functions and is essential for viability in the protozoan parasites, Leishmania major and Trypanosoma brucei. In our investigations to define the essential downstream targets of NMT, we have focused on the ARF (ADP-ribosylation factor) family of proteins, as growth arrest in Saccharomyces cerevisiae mutants with reduced NMT activity correlates with decreased modification of members of this group of proteins. We have identified nine ARF/ARLs (where ARL stands for ARF-like) encoded in the T. brucei and T. cruzi genomes and ten in L. major. The T. brucei ARL1 protein is expressed only in the mammalian bloodstream form of the parasite, in which it is localized to the Golgi apparatus. RNAi (RNA interference) has been used to demonstrate that ARL1 is essential for viability in these infective cells. Before cell death, depletion of ARL1 protein results in disintegration of the Golgi structure and a delay in exocytosis of the abundant GPI (glycosylphosphatidylinositol)-anchored VSG (variant surface glycoprotein) to the parasite surface.