The GLUT protein family is a member of the major facilitator superfamily of membrane transporters and is encoded by the SLC2 genes. GLUT proteins contain 12 membrane-spanning domains, an N-linked glycosylation site, and intracellular NH₂ and COOH termini. In addition there are several conserved residues and motifs designated “sugar transporter signatures”.
To date, 14 GLUT isoforms have been identified and divided into 3 different classes based on sequence similarity and structural and functional characteristics. GLUT4 together with GLUT 1-3 and 14 belong to Class I.