Evolution of protein trafficking in kinetoplastid parasites: Complexity and pathogenesis

The kinetoplastida and their close relatives are unicellular organisms prevalent within the biosphere and important for significant impacts on global health, economy and ecosystems. They are, under most models, an early branching lineage. Individual species adapted to highly diverse environments by adopting complex life styles; parasitic species can infect a wide range of eukaryotic hosts, while many relatives are free-living and some autotrophic from acquiring a plastid for photosynthesis. Adaptation is especially evident in the evolution of kinetoplastid cell surface architecture and is supported by endomembrane trafficking and serves as a platform for interaction with its environment. Here we summarize and discuss recent genomic and experimental studies of the protein trafficking system in kinetoplastids, with focus on the composition and function of the surface as well as mechanisms for constructing, maintaining and regulating the cell surface proteome. We hope this provides a broad view of how protein trafficking contributes to the intricate and dynamic host-parasite interfaces that are critical for successful environmental adaptation of this highly important lineage. The major differentiation between prokaryotic and eukaryotic cells is a sophisticated system of subcellular organelles in the latter. The vast majority are the product of endogenous evolutionary events, and several paralogous families (Rabs, SNAREs and others) with specific localizations to one or more compartments has allowed predictions of intracellular structure based on gene complements and comparative genomics. Here we consider one lineage, the kinetoplastids, that have been rather well studied, to extract how evolutionary events can mold trafficking.