Characterization and evaluation of a distinct fusion ability in the functionally related cyclic amidohydrolase family enzymes

The cyclic amidohydrolase family enzymes, which include allantoinase, dihydroorotase, dihydropyrimidinase and (phenyl)hydantoinase, are metal-dependent hydrolases and play a crucial role in the metabolism of purine and pyrimidinein vivo. Each enzyme has been independently characterized, and thus well documented, but studies on the higher structural traits shared by members of this enzyme family are rare due to the lack of comparative study. Here, we report upon the expression inE. coli cells of maltose-binding protein (MBP)- and glutathione S-transferase (GST)-fused cyclic amidohydrolase family enzymes, facilitating also for both simple purification and high-level expression. Interestingly, the native quaternary structure of each enzyme was maintained even when fused with MBP and GST. We also found that in fusion proteins the favorable biochemical properties of family enzymes such as, their optimal pHs, specific activities and kinetic properties were conserved compared to the native enzymes. In addition, MBP-fused enzymes showed remarkable folding abilityin-vitro. Our findings, therefore, suggest that a previously unrecognized trait of this family, namely the ability to functional fusion with some other protein but yet to retain innate properties, is conserved. We described here the structural and evolutionary implications of the properties in this family enzyme.