Purine ribonucleoside efflux pump NepI and similar transporters of the Major Facilitator Superfamily
This family is composed of purine efflux pumps such as Escherichia coli NepI and Bacillus subtilis PbuE, sugar efflux transporters such as Corynebacterium glutamicum arabinose efflux permease, multidrug resistance (MDR) transporters such as Streptomyces lividans chloramphenicol resistance protein (CmlR), and similar proteins. NepI and PbuE are involved in the efflux of purine ribonucleosides such as guanosine, adenosine and inosine, as well as purine bases like guanine, adenine, and hypoxanthine, and purine base analogs. They play a role in the maintenance of cellular purine base pools, as well as in protecting the cells and conferring resistance against toxic purine base analogs such as 6-mercaptopurine. MDR transporters are drug/H+ antiporters (DHA) that mediate the efflux of a variety of drugs and toxic compounds, and confer resistance to these compounds. The NepI-like family belongs to the Major Facilitator Superfamily (MFS) of membrane transport proteins, which are thought to function through a single substrate binding site, alternating-access mechanism involving a rocker-switch type of movement.
Feature 1:putative chemical substrate binding pocket [chemical binding site]
Evidence:
Comment:based on the structures of MFS transporters with bound substrates, substrate analogs, and/or inhibitors
Comment:since MFS proteins facilitate the transport of many different substrates including ions, sugar phosphates, drugs, neurotransmitters, nucleosides, amino acids, and peptides, the residues involved in substrate binding may not be strictly conserved among superfamily members
Comment:the substrate binding site or translocation pore has access to both sides of the membrane in an alternating fashion through a conformational change of the MFS transporter
Jiyao W et al.(2023). "The conserved domain database in 2023.",