The solute carrier (SLC) group of membrane transport proteins include over 400 members organized into 66 families.
Solutes that are transported by the various SLC group members are extremely diverse and include both charged and uncharged organic molecules as well as inorganic ions and the gas ammonia.
As is typical of integral membrane proteins, SLCs contain a number of hydrophobic transmembrane alpha helices connected to each other by hydrophilic intra- and extra-cellular loops.
By convention of the nomenclature system, members within an individual SLC family have greater than 20-25% sequence identity to each other.
An exception occurs with SLC family 21[5] (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.