Crystal Structure and Sequence Analysis of N⁵, N¹⁰-Methylenetetrahydrofolate Dehydrogenase/Cyclohydrolase Enzyme from Porphyromonas gingivalis

The methylenetetrahydrofolate dehydrogenase-cyclohydrolase (FolD) enzyme has a dual activity of N5,N10-methylenetetrahydrofolate dehydrogenase and cyclohydrolase. This enzyme plays a critical role in the chemical modification of tetrahydrofolate, which is an important coenzyme involved in the synthesis of DNA, RNA, and amino acids. Therefore, bacterial FolD has been studied as a potential drug target for the development of antibiotics. Here, we determined the crystal structure of FolD (PgFolD) from the oral pathogen Porphyromonas gingivalis at 2.05 & Aring; resolution using the molecular replacement method. The crystal structure of PgFolD was successfully refined to a crystallographic R-factor of 21.4% (R-free = 23.8%). The crystals belong to the space group of P4(3)22 with the unit cell parameters of a = 110.7 & Aring;, b = 110.7 & Aring;, and c = 69.8 & Aring;, containing one subunit in the asymmetric unit. Our analytical size-exclusion chromatography results indicated that PgFolD forms a stable dimer in solution. Additionally, structural and sequence comparison studies with previously known FolDs revealed that PgFolD has a different substrate-binding site residue composition. These findings provide valuable insights for the structure-based development of specific inhibitors against the Porphyromonas gingivalis pathogen.