A menaquinone biosynthetic enzyme exhibits the type 2 periplasmic-binding protein fold
This group includes Ttha1568 (MqnD) from Thermus thermophilies HB8, an enzyme within an alternative menaquinone biosynthetic pathway that catalyzes the conversion of cyclic de-hypoxanthine futalosine to 1,4-dihydroxy-6-naphthoate. Menaquinone (MK; vitamin K) is an essential lipid-soluble carrier that shuttles electrons between membrane-bound protein complexes in the electron transport chain. Ttha1568 has significant structural homology with the members of type 2 periplasmic-binding fold protein superfamily. The PBP2 proteins are typically comprised of two globular subdomains connected by a flexible hinge and bind their ligand in the cleft between these domains in a manner resembling a Venus flytrap.
Jiyao W et al.(2023). "The conserved domain database in 2023.",