The homologous glucose transport proteins of prokaryotes and eukaryotes

Genes or cDNA encoding sugar transport proteins have recently been isolated from a variety of prokaryote and eukaryote organisms. By sequencing the cloned DNA, the amino acid sequences of the transport proteins have been predicted and found to comprise a homologous family extending from cyanobacteria through yeasts, algae and protozoa to mammals, including rat, mouse and man. By aligning all the sequences and comparing them with those of membrane transport proteins for other sugars, we can deduce which features of the primary sequences are critical for maintenance of structure and function. Furthermore, the conservation of extended hydrophobic and hydrophilic regions enables the construction of a consensus model of their arrangement in the membrane. Specific sequence motifs are identified and their occurrence in otherwise apparently unrelated bacterial transport proteins for citrate and tetracycline are discussed.