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Cation and sugar selectivity determinants in a novel family of transport proteins
Author(s) -
Poolman Bert,
Knol Jan,
Van Der Does Chris,
Henderson Peter J. F.,
Liang WeiJun,
Leblanc Gérard,
Pourcher Thierry,
MusVeteau Isabelle
Publication year - 1996
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1046/j.1365-2958.1996.397949.x
Subject(s) - pep group translocation , biology , biochemistry , mutant , membrane transport protein , transport protein , permease , escherichia coli , phosphoenolpyruvate carboxykinase , membrane protein , melibiose , gene , membrane , enzyme , maltose
A new family of homologous membrane proteins that transport galactosides–pentoses–hexuronides (GPH) is described. By analysing the aligned amino acid sequences of the GPH family, and by exploiting their different specificities for cations and sugars, we have designed mutations that yield novel insights into the nature of ligand binding sites in membrane proteins. Mutants have been isolated/constructed in the melibiose transport proteins of Escherichia coli Klebsiella pneumoniae and Salmonella typhimurium , and the lactose transport protein of Streptococcus thermophilus which facilitate uncoupled transport or have an altered cation and/or substrate specificity. Most of the mutations map in the amino‐terminal region, in or near amphipathic α‐helices II and IV, or in interhelix‐loop 10–11 of the transport proteins. On the basis of the kinetic properties of these mutants, and the primary and secondary structure analyses presented here, we speculate on the cation binding pocket of this family of transporters. The regulation of the transporters through interaction with, or phosphorylation by, components of the phosphoenolpyruvate:sugar phosphotransferase system is also discussed.