Authors: Smith SS, Pfluger SL, Hjort E, McArthur AG, Hager KM
Coatomer coated (COPI) vesicles play a pivotal role for multiple
membrane trafficking steps throughout the eukaryotic cell. Our focus
is on betaCOP, one of the most well known components of the COPI
multi-protein complex. Amino acid differences in betaCOP 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 betaCOP amino
acid sequences was conducted for 49 eukaryotic species. Cloning and
sequence analysis of the Toxoplasma gondii betaCOP homologue 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 betaCOP 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 betaCOP
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 TgbetaCOP
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 betaCOP.
