Solute carrier family 45 and similar sugar transporters of the Major Facilitator Superfamily of transporters
This group includes the solute carrier 45 (SLC45) family as well as plant sucrose transporters (SUCs or SUTs) and similar proteins such as Schizosaccharomyces pombe general alpha-glucoside permease. the SLC45 family is composed of four (A1-A4) vertebrate proteins as well as related insect proteins such as Drosophila sucrose transporter SCRT or Slc45-1. Members of this group transport sucrose and other sugars like maltose into the cell, with the concomitant uptake of protons (symport system). Plant sucrose transporters are crucial to carbon partitioning, playing a key role in phloem loading/unloading. They play a key role in loading and unloading of sucrose into the phloem and as a result, they control sucrose distribution throughout the whole plant and drive the osmotic flow system in the phloem. They also play a role in the exchange of sucrose between beneficial symbionts (mycorrhiza and Rhizobium) as well as pathogens such as nematodes and parasitic fungi. There are nine sucrose transporter genes in Arabidopsis and five in rice. Vertebrate SLC45 family proteins have been implicated in the regulation of glucose homoeostasis in the brain (SLC45A1), with skin and hair pigmentation (SLC45A2), and with prostate cancer and myelination (SLC45A3). Mutations in SLC45A2, also called MATP (membrane-associated transporter protein) or melanoma antigen AIM1, cause oculocutaneous albinism type 4 (OCA4), an autosomal recessive disorder of melanin biosynthesis that results in congenital hypopigmentation of ocular and cutaneous tissues. The SLC45 family and related sugar transporters belong 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.",