title: Decreased function of the class B tetracycline efflux protein Tet with mutations at aspartate 15, a putative intramembrane residue.
abstract: The aspartate 15 residue within the first predicted intramembrane helix of the tetracycline efflux protein Tet has been conserved in four tetracycline resistance determinants from gram-negative bacteria. Its replacement in class B Tet by tyrosine, histidine, or asparagine resulted in a 60 to 85% loss of tetracycline resistance and a similar loss of tetracycline-proton antiport. The tyrosine and histidine substitutions lowered the Vmax of the efflux system by some 90% but did not alter the Km. The asparagine substitution raised the Km over 13-fold, while the Vmax was equal to or greater than that of the wild type. Therefore, although the nature of its role is unclear, aspartate 15 is important for normal Tet function.
authors.affiliation: Department of Molecular Biology, Tufts University School of Medicine, Boston, Massachusetts 02111.
authors.forename: L M
authors.initials: LM
authors.lastname: McMurry
authors.forename: M
authors.initials: M
authors.lastname: Stephan
authors.forename: S B
authors.initials: SB
authors.lastname: Levy
mesh_terms: D001224:Aspartic Acid; D001483:Base Sequence; D002352:Carrier Proteins / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics*; D008565:Membrane Proteins / Q000235:genetics; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D011522:Protons; D011815:R Factors / Q000235:genetics*; D012097:Repressor Proteins / Q000235:genetics*; D015183:Restriction Mapping; D013329:Structure-Activity Relationship; D013752:Tetracycline / Q000378:metabolism*; D013753:Tetracycline Resistance / Q000235:genetics
chemical_list: D002352:Carrier Proteins; D008565:Membrane Proteins; D011522:Protons; D012097:Repressor Proteins; C034811:tetracycline resistance-encoding transposon repressor protein; D001224:Aspartic Acid; D013752:Tetracycline