Family 2.A.71 - The Folate-Biopterin Transporter Family       

Family ID: 52645

The FBT family includes functionally characterized members only from protozoa, but homologues are found in blue-green bacteria (Synechocystis) and plants (Arabidopsis thaliana). The functionally characterized members of the family include FT1, the major folate transporter, and BT1, the biopterin/folate transporter. There are at least 6 homologues of the FT1 transporter in Leishmania carried in a tandem array, but the genetic data suggest that only FT1 has appreciable activity (S. Beverley, personal communication). A related protein in Trypanosoma brucei, ESAGIO, shows weak folate/biopterin transport activity.

Proteins of the FBT family are reported to contain 686 aas (T. brucei), 627-631 aas (Leishmania species), 408-431 aas (A. thaliana) and 453 or 494 aas (cyanobacteria). All probably have 12 transmembrane a-helical spanners (TMSs). They may function by H+ symport. PSI-BLAST results with two iterations suggest that the FBT family is a distant family within the major facilitator superfamily (MFS; TC #2.A.1), most closely related to drug resistance permeases and the putative bacteriochlorophyll delivery (BCD) family (TC #9.B.7), also believed to be related to the MFS.