2.A.71 The Folate-Biopterin Transporter (FBT) Family
The FBT family includes functionally characterized members from protozoa, cyanobacteria (Synechocystis) and plants (Arabidopsis thaliana). Functionally characterized members of the family include FT1 (TC# 2.A.71.1.3), the major protozoan folate transporter, BT1 (2.A.71.1.2), the biopterin/folate transporter and AdoMetT1, the major S-adenosylmethionine uptake porter (2.A.71.1.5). There are at least 6 homologues of the FT1 transporter in Leishmania encoded by tandem genes. A related protein in Trypanosoma brucei, ESAGIO, shows weak folate/biopterin transport activity.
Proteins of the FBT family are reported to contain 627-631 aas (Leishmania species), 408-431 aas (A. thaliana) and 453-494 aas (cyanobacteria). All probably have 12 TMSs. They may function by H+ symport. The FBT family is a distant family within the major facilitator superfamily (MFS; TC #2.A.1).
The probable transport reaction catalyzed by characterized FBT family members is:
[folate, biopterin or AdoMet] (out) + nH+ (out) → [folate, biopterin or AdoMet] (in) + nH+ (in)