Evolutionary variations of VPS29, and their implications for the heteropentameric model of retromer

The retromer complex is conserved across all eukaryotic species and functions in physiologically important sorting processes at the endosomal membrane. A key component of retromer is the VPS29 protein that, although structurally similar to phospho-diesterases, has been convincingly shown in the recent study by Swarbrick et al. (PLoS One 6:e20420, 2011) to be a rigid scaffold that interacts with various proteins that function with retromer in endosomal protein sorting. A widely held view, based on initial observations in Saccharomyces cerevisiae, is that retromer functions as a stable heteropentamer. This is, however, contrary to experimental data presented in Swarbrick et al. (and in other studies) that indicate that retromer in higher eukaryotes is a looser association of two subcomplexes that respectively mediate cargo-selection and membrane tubulation. Here we present an analysis of evolutionary variation of the VPS29 protein and discuss why the retromer complex as first characterized in S. cerevisiae is not representative of retromer in other eukaryotic taxa.