Citrate-proton symporter of the Major Facilitator Superfamily of transporters
Citrate-proton symporter, also called citrate carrier protein or citrate transporter or citrate utilization protein A (CitA), is a proton symporter that functions in the uptake of citrate across the boundary membrane. It allows the utilization of citrate as a sole source of carbon and energy. In Klebsiella pneumoniae, the gene encoding this protein is called citH, instead of citA, which is the case for Escherichia coli and other organisms. CitA belongs to the Metazoan Synaptic Vesicle Glycoprotein 2 (SV2) and related small molecule transporter family (SV2-like) of the Major Facilitator Superfamily (MFS) of membrane transport proteins. MFS proteins 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.",