The role of the V-ATPase subunit d for structural and functional coupling VI and Vo subunits within the yeast V-ATPase complex is under study in our lab. Because high-resolution structures of the yeast V-ATPase subunit d are not available, the crystal structure of its homologue from the archeabacteria Thermus thermophilus at 1.95A resolution (PDB ID code IR5Z) served as structural model for this study. We are performing complementation studies aimed to establish structure-function conservation analysis of this subunit. Heterologous complementation of T. thermophilus subunit d in yeast would be further supported by mutagenesis analyses. Overall, atpC is a decent model for yeast subunit d. Our study shows that atpC is similar enough to structurally replace d, however, functionality was not observed with heterologous expression.