PMID:14503872
| Citation |
Green, AL, Hrodey, HA and Brooker, RJ (2003) Evidence for structural symmetry and functional asymmetry in the lactose permease of Escherichia coli. Biochemistry 42:11226-33 |
|---|---|
| Abstract |
Previous work on the lactose permease of Escherichia coli has shown that mutations along a face of predicted transmembrane segment 8 (TMS-8) play a critical role in conformational changes associated with lactose transport (Green, A. L., and Brooker, R. J. [2001] Biochemistry 40, 12220-12229). Substitutions at positions 261, 265, 268, 272, and 276, which form a continuous stripe along TMS-8, were markedly defective for lactose transport velocity. In the current study, three single mutants (F261D, N272Y, N272L) and a double mutant (T265Y/M276Y) were chosen as parental strains for the isolation of mutants that restored transport function. A total of 68 independent mutants were isolated and sequenced. Forty-four were first-site revertants in which the original mutation was changed back to the wild-type residue or to a residue with a similar side-chain volume. The other 24 mutations were second-site suppressors in TMS-2 (Q60L, Q60P), loop 2/3 (L70H), TMS-7 (V229G/A), TMS-8 (F261L), and TMS-11 (F354V, C355G). On the basis of their locations, the majority of the second-site suppressors can be interpreted as improving the putative TMS-2/TMS-7/TMS-11 interface to compensate for conformational defects imposed by mutations in TMS-8 that disrupt the putative TMS-1/TMS-5/TMS-8 interface. Overall, this paper suggests that the TMS-2/TMS-7/TMS-11 interface is more important from a functional point of view, even though there is compelling evidence for structural symmetry between the two halves of the permease. |
| Links |
PubMed Online version:10.1021/bi034810+ |
| Keywords |
Amino Acid Substitution; Biological Transport/genetics; Escherichia coli/cytology; Escherichia coli/enzymology; Escherichia coli/genetics; Escherichia coli Proteins/chemistry; Escherichia coli Proteins/genetics; Escherichia coli Proteins/metabolism; Genotype; Lactose/metabolism; Melibiose/metabolism; Membrane Proteins/chemistry; Membrane Proteins/genetics; Membrane Proteins/metabolism; Membrane Transport Proteins/chemistry; Membrane Transport Proteins/genetics; Membrane Transport Proteins/metabolism; Models, Molecular; Monosaccharide Transport Proteins; Phenotype; Plasmids/genetics; Protein Conformation; Suppression, Genetic; Symporters |
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