Molecular evolution of the vesicle coat component βCOP in Toxoplasma gondii

Coatomer coated (COPI) vesicles play a pivotal role for Multiple membrane trafficking steps throughout the eukaryotic cell. Our focus is on beta COP. one of the most well known components of the COPI multi-protein complex. Amino acid differences in COP may dictate functional divergence across species during the course of evolution, especially with regards to the evolutionary pressures on obligate intracellular parasites. A bioinformatic analysis of COP amino acid sequences was conducted for 49 eukaryotic species. Cloning and sequence analysis of the Toxoplasma gondii COP hornologue revealed several amino acid insertions unique to T gondii and one C-terminal insertion that is unique to apicomplexan parasites. These findings led us to investigate the possibility that beta COP experienced functional divergence during the course of its evolution. Bayesian phylogenetic analysis revealed a tree consistent with pan eukaryote distribution and long-branch lengths were observed among the apicomplexans. Further analysis revealed that kinetoplast COP underwent the most amount of change, leading to perhaps an overall change of function. In comparison, T gondii exhibited subtle yet specific amino acid changes. The amino acid substitutions did not occur in the same places as other lineages, suggesting that Tg beta COP has a role specific to the apicomplexans. Our work identifies 48 residues that are likely to be functionally important when comparing apicomplexan, kinetoplastid, and fungal beta COP. (c) 2007 Elsevier Inc. All rights reserved.