The conserved hypothetical protein Af1704 exhibits the type 2 periplasmic-binding protein fold
This group includes the Af1704 protein from from Archaeoglobus fulgidus DSM 4304, which is an ortholog of Ttha1568 (MqnD) from Thermus thermophilies HB8. MqnD is 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. Af1704 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.",