Solute carrier family

The SoLute Carrier (SLC) group of membrane transport proteins include over 300 members organized into 47 families. The SLC gene nomenclature system was originally proposed by the Human Genome Organization (HUGO) and is the basis for the official HUGO names of the genes that encode these transporters.

Solutes that are transported by the various SLC group members are extraordinarily diverse and include both charged and uncharged organic molecules as well as inorganic ions.

As is typical of integral membrane proteins, SLCs contain a number of hydrophobic transmembrane alpha helices connected to each other by hydrophilic intra- or extra-cellular loops. Depending on the SLC, these transporters are functional as either monomers or obligate homo- or hetero-olgiomers.

Scope
By convention of the nomenclature system, members within an individual SLC family have greater than 20% sequence homology to each other. In contrast, the homology between SLC families is very low to non-existent. Hence the criteria for inclusion of a family into the SLC group is not evolutionary relatedness to other SLC families but rather functional (i.e., an integral membrane protein which transports a solute).

The SLC group include examples of transport proteins that are:


 * facilitative transporters (allow solutes to flow downhill with their electrochemical gradients)
 * secondary active transporters (allow solutes to flow uphill against their electrochemical gradient by coupling to transport of a second solute that flows downhill with its gradient such that the overall free energy change is still favorable)

The SLC series does not include members of transport protein families which have previously been classified by other widely accepted nomenclature systems including:


 * primary active transporters (allow flow uphill against electrochemical gradients) such as ABC (ATP Binding Cassette) transporters by coupling transport to an energy releasing event such as ATP hydrolysis
 * ion channels
 * aquaporins (water channels)

Subcellular distribution
Most members of the SLC group are located in the outer cell membrane, but some members are located in mitochondria (most notably SLC family 25) or other intracellular organelles.

Nomenclature system
Names of individual SLC members have the following format:


 * SLCnXm

where n = an integer representing a family (e.g., 1-47),

X = a single letter (A, B, C, ...) denoting a subfamily, and

m = an integer representing an individual family member (isoform).

For example SLC1A1 is the first isoform of subfamily A of SLC family 1.

An exception occurs with SLC family 21 (the organic anion transporting polypeptide transporters) which for historical reasons have names in the format SLCOnXm where n = family number, X = subfamily letter, and m = member number.

While the HUGO nomenclature system by definition only includes human genes, the nomenclature system has been informally extended to include rodent species through the use of lower cases letters (e.g., Slc1a1 denotes the rodent ortholog of the human SLC1A1 gene).

Families

 * (1) high affinity glutamate and neutral amino acid transporter
 * (2) facilitative GLUT transporter
 * (3) heavy subunits of heteromeric amino acid transporters
 * (4) bicarbonate transporter
 * (5) sodium glucose cotransporter
 * (6) sodium- and chloride- dependent neurotransmitter transporter
 * (7) cationic amino acid transporter/glycoprotein-associated
 * (8) Na+/Ca2+ exchanger
 * (9) Na+/H+ exchanger
 * (10) sodium bile salt cotransport
 * (11) proton coupled metal ion
 * transporter
 * (12) electroneutral cation-Cl cotransporter
 * (13) human Na+-sulfate/carboxylate cotransporter
 * (14) urea transporter
 * (15) proton oligopeptide cotransporter
 * (16) monocarboxylate transporter
 * (17) vesicular glutamate transporter
 * (18) vesicular amine transporter
 * (19) folate/thiamine transporter
 * (20) type III Na+-phosphate cotransporter
 * (21) organic anion transporting
 * subfamily 1
 * subfamily 2
 * subfamily 3
 * subfamily 4
 * subfamily 5
 * subfamily 6
 * (22) organic cation/anion/zwitterion transporter
 * (23) Na+-dependent ascorbic acid transporter
 * (24) Na+/(Ca2+-K+) exchanger
 * (25) mitochondrial carrier
 * (26) multifunctional anion exchanger
 * (27) fatty acid transport protein
 * (28) Na+-coupled nucleoside transport
 * (29) facilitative nucleoside transporter
 * (30) zinc efflux
 * (31) copper transporter
 * (32) vesicular inhibitory amino acid transporter
 * (33) Acety-CoA transporter
 * (34) type II Na+-phosphate cotransporter
 * (35) nucleoside-sugar transporter
 * subfamily A
 * subfamily B
 * subfamily C
 * subfamily D
 * subfamily E
 * (36) proton-coupled amino acid transporter
 * (37) sugar-phosphate/phosphate exchanger
 * (38) System A & N, sodium-coupled neutral amino acid transporter
 * (39) metal ion transporter
 * (40) basolateral iron transporter
 * (41) MgtE-like magnesium transporter
 * (42) Rh ammonium transporter
 * (43) Na+-independent, system-L like amino acid transporter
 * (44) Choline-like transporter
 * (45) Putative sugar transporter
 * (46) Heme transporter
 * (47) multidrug and toxin extrusion
 * (28) Na+-coupled nucleoside transport
 * (29) facilitative nucleoside transporter
 * (30) zinc efflux
 * (31) copper transporter
 * (32) vesicular inhibitory amino acid transporter
 * (33) Acety-CoA transporter
 * (34) type II Na+-phosphate cotransporter
 * (35) nucleoside-sugar transporter
 * subfamily A
 * subfamily B
 * subfamily C
 * subfamily D
 * subfamily E
 * (36) proton-coupled amino acid transporter
 * (37) sugar-phosphate/phosphate exchanger
 * (38) System A & N, sodium-coupled neutral amino acid transporter
 * (39) metal ion transporter
 * (40) basolateral iron transporter
 * (41) MgtE-like magnesium transporter
 * (42) Rh ammonium transporter
 * (43) Na+-independent, system-L like amino acid transporter
 * (44) Choline-like transporter
 * (45) Putative sugar transporter
 * (46) Heme transporter
 * (47) multidrug and toxin extrusion
 * (39) metal ion transporter
 * (40) basolateral iron transporter
 * (41) MgtE-like magnesium transporter
 * (42) Rh ammonium transporter
 * (43) Na+-independent, system-L like amino acid transporter
 * (44) Choline-like transporter
 * (45) Putative sugar transporter
 * (46) Heme transporter
 * (47) multidrug and toxin extrusion
 * (43) Na+-independent, system-L like amino acid transporter
 * (44) Choline-like transporter
 * (45) Putative sugar transporter
 * (46) Heme transporter
 * (47) multidrug and toxin extrusion
 * (46) Heme transporter
 * (47) multidrug and toxin extrusion
 * (47) multidrug and toxin extrusion
 * (47) multidrug and toxin extrusion