Golgi_traff phylogeny reveals ancient eukaryotic genes with recent surprises: replication and diversification of HID1 domain-containing protein unique to Schizosaccharomyces.

Golgi_traff is a Pfam clan containing two members, Dymeclin (DYM) and HID1 domain-containing protein (HID). Interrogation of over 900 eukaryotic genomes with sequence models showed that both are ancient eukaryotic genes, which have exhibited different paths of gene loss, including from major taxonomic groups. For example, the Metazoa have both genes, whereas the Viridiplantae and Dikarya have lost HID and DYM, respectively. A unique replication event occurred within the genus Schizosaccharomyces in that all sequenced species possess three HID-encoding paralogs, whereas its nearest fungal relatives and other eukaryotes are almost exclusively monogenic. A phylogenetic analysis of yeasts revealed that the Golgi-resident paralog Human ortholog 3 (SPAC17A5.16) is more similar to the HID of other yeasts than to its paralogs. Transmission electron microscopy revealed that the SPAC17A5.16 mutant lacks a stacked Golgi apparatus (GA) form, suggesting a role in maintaining GA structure. Altered proliferation of the SPAC17A5.16 mutant in response to GA disrupting chemical agents indicated a perturbation of GA-related functions. Structural models suggest SPAC17A5.16 has a long, disordered N-terminal region that may facilitate anchoring to GA membranes. A modification to Schizosaccharomyces HID nomenclature is proposed to reflect their evolutionary and functional characteristics. The potential of the Golgi_traff clan to serve as a model for the diversification of protein function according to the concepts of sub/neofunctionalization is discussed.