Family 2.A.38 - The K+ Transporter Family       

Family ID: 52633

The proteins of the Trk family are derived from Gram-negative and Gram-positive bacteria, yeast and plants. The proteins of E. coli K12 (TrkH and TrkG) as well as several yeast and plant proteins have been functionally an topologically characterized. While TrkH is generally present in E. coli and other enteric bacteria, TrkG is encoded by a foreign gene located within the prophage rac region of the E. coli K12 chromosome. TrkG is not present in several other E. coli strains. The sizes of the Trk family members vary from 423 residues to 1235 residues. The bacterial proteins are of 423-558 residues, the Triticum aestivum protein is 533 residues, and the yeast proteins vary between 841 and 1241 residues. These proteins possess 8 putative transmembrane a-helical spanners. An 8 TMS topology with N- and C-termini on the inside, has been established for AtHKT1 (Kato et al., 2001).

The phylogenetic tree reveals that the proteins cluster according to phylogeny of the source organism with (1) the Gram-negative bacterial Trk proteins, (2) the Gram-negative and Gram-positive bacterial Ktr proteins, (3) the yeast proteins and (4) the plant proteins comprising four distinct clusters (Saier et al., 1999). S. cerevisiae possesses two paralogues, high- and low-affinity K+ transporters.