Crystal Structure of Oxalate Decarboxylase from Photorhabdus luminescens, A Symbiotic Bacterium Associated with Entomopathogenic Nematodes

Photorhabdus luminescens is a Gram-negative, symbiotic bacterium associated with entomopathogenic nematodes of the genus Heterorhabditis. Several genes from this organism related to insecticidal properties are being examined for their potential in pest management. Oxalate decarboxylase (OXDC), an enzyme secreted by bacteria and fungi and putatively associated with insecticidal pathways catalyses the manganese dependent decarboxylation of oxalate to formate and CO₂. In this study, we report the X-ray crystal structure of OXDC isolated and purified from Photorhabdus luminescens (PlOXDC, MW 43 kDa) determined at 1.97 Å resolution. PlOXDC protomer has a bicupin structure. Each cupin domain consists of two antiparallel β sheets organized as a sandwich with a Mn²⁺ ion bound at the active site. PlOXDC exists as a mixture of monomeric and trimeric forms in solution but assumes a trimeric form in the crystal structure.