Alteration of oligomeric state and domain architecture is essential for functional transformation between transferase and hydrolase with the same scaffold

Transferases and hydrolases catalyze different chemical reactions and express different dynamic responses upon ligand binding. To insulate the ligand molecule from the surrounding water, transferases bury it inside the protein by closing the cleft, while hydrolases undergo a small conformational change and leave the ligand molecule exposed to the solvent. Despite these distinct ligand-binding modes, some transferases and hydrolases are homologous. To clarify how such different catalytic modes are possible with the same scaffold, we examined the solvent accessibility of ligand molecules for 15 SCOP superfamilies, each containing both transferase and hydrolase catalytic domains. In contrast to hydrolases, we found that nine superfamilies of transferases use two major strategies, oligomerization and domain fusion, to insulate the ligand molecules. The subunits and domains that were recruited by the transferases often act as a cover for the ligand molecule. The other strategies adopted by transferases to insulate the ligand molecule are the relocation of catalytic sites, the rearrangement of secondary structure elements, and the insertion of peripheral regions. These findings provide insights into how proteins have evolved and acquired distinct functions with a limited number of scaffolds.