Menaquinone biosynthetic enzyme and related hypothetical proteins; the type 2 periplasmic-binding protein fold
This family represents MqnD, an enzyme within the alternative menaquinone biosynthetic pathway, and related conserved hypothetical proteins. Menaquinone (MK; vitamin K) is an essential lipid-soluble carrier that shuttles electrons between membrane-bound protein complexes in the electron transport chain. The members include Ttha1568, MqnD from Thermus thermophiles HB8, and the conserved hypothetical proteins SCO4506 from Streptomyces coelicolor, Af1704 from Archaeoglobus DSM 4304, Dr0370 from Deinococcus radiodurans, and Ca3427 from candida albicans. They all have significant structural homology with the members of type 2 periplasmic-binding fold protein superfamily (PBP2). 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.",