The Major Facilitator Superfamily (MFS) is the largest superfamily of secondary carriers known. It includes a few families of proteins that catalyze processes other than secondary transport. For example, evidence suggests that the Major Intrinsic Protein (MIP) family of aquaporins and glycerol channels is related to the MFS as are Rhomboid proteases and the glycosyl transferase (GT) superfamily (unpublished observations).
Chang A.B., Lin R., Studley W.K., Tran C.V., Saier M.H. Jr. 2004. Phylogeny as a Guide to Structure and Function of Membrane Transport Proteins. Mol Membr Biol. 21(3):171-81.
Reddy, V.S., M.A. Shlykov, R. Castillo, E.I. Sun, and M.H. Saier, Jr. (2012). The major facilitator superfamily (MFS) revisited. FEBS J. 279: 2022-2035.
2.A.1 - The Major Facilitator Superfamily (MFS)
Yen, M.R., J.S. Chen, J.L. Marquez, E.I. Sun, and M.H. Saier. (2010). Multidrug resistance: phylogenetic characterization of superfamilies of secondary carriers that include drug exporters. Methods Mol Biol 637: 47-64.
2.A.2 - The Glycoside-Pentoside-Hexuronide (GPH):Cation Symporter Family
2.A.12 - The ATP:ADP Antiporter (AAA) Family
2.A.17 - The Proton-dependent Oligopeptide Transporter (POT/PTR) Family
2.A.48 - The Reduced Folate Carrier (RFC) Family
2.A.57 - The Equilibrative Nucleoside Transporter (ENT) Family
2.A.60 - The Organo Anion Transporter (OAT) Family
2.A.71 - The Folate-Biopterin Transporter (FBT) Family
2.A.100 - The Ferroportin (Fpn) Family
2.A.125 - The Eukaryotic Riboflavin Transporter (E-RFT) Family
4.D.2 - The Glycosyl Transferase 2 (GT2) Family
9.B.111 - The 6 TMS Lysyl tRNA Synthetase (LysS) Family