Substrate and cofactor binding interaction studies of galactitol -1- Phosphate 5- Dehydrogenase from Peptoclostridium difficile

Abstract

Tagatose is a high value low calorie sweetener that is used as a sugar substitute in the food and pharmaceutical industry. The production of tagatose requires the conversion of galactitol-1-phosphate to tagatose-6-phosphate by galactitol-1-phosphate 5-dehydrogenase (PdGPDH). Theobjective of this work is to study the protein-ligand interaction between PdGPDH and its ligands; galactitol-1-phosphate, Zn2+ and NAD+. Understanding of this mechanism will provide an insight into the possible catalytic events in these domains, thus providing information for potential protein engineering to improve the tagatose production. A 3D model of PdGPDH was constructed to identify the catalytic and coenzyme binding domains. In order to understand the interaction of PdGPDH with its ligands, a docking analysis of PdGPDH-substrate, PdGPDH-Zn2+ and PdGPDH-NAD+ complex was performed using CDOCKER in Discovery Studio 4.0 (DS 4.0). A series of docking events were performed to find the most stable binding interaction for the enzyme and its ligands. This study found that Cys 37, His 58, Glu 59, Glu 142 residues from PdGPDH form an active site pocket similar to known GPDH. A catalytic Zn2+ binding domain and a cofactor NAD+binding domain with strong hydrogen bonding contacts with the substrate and the cofactor were identified. The binding pockets of the enzyme for galactitol-1-phosphate, NAD+ and Zn2+has been defined. The stability of PdGPDH with its ligand was verified by utilizing the molecular dynamic simulation of docked complex. The results from this study will assist future mutagenesis study and enzyme modification work to improve the tagatose production.