A change of threonine 266 to isoleucine in the lac permease of Escherichia coli diminishes the transport of lactose and increases the transport of maltose

Abstract

The DNA sequence of several functionally interesting lac permease mutants of Escherichia coli has been determined. The phenotypes of the mutant permeases were described by Mieschendahl et al. (1981). The following exchanges are noteworthy: tyr to asp in codon 26 in Y-K MUB 7; thr to ile in codon 266 in Y-K AJ 33; gly to asp in codon 262 in Y-D 3 and in Y-D 4.

Secondary solute transport in bacteria

“…Strategies for isolating LacY mutants with interesting phenotypes have largely been based on selection for resistance to inhibition by toxic sugar analogs (e.g., cellobiose, TDG) and the ability to grow on sugars that are not substrates of the wild-type protein (e.g., maltose, sucrose) [285][286][287][288]. Single mutations which cause an increased ability to transport maltose (an a-glucoside; enhanced recognition for maltose, although some mutants also transport faster) are at positions Ala-177, Tyr-236, Thr-266, Ser-306, and Ala-389 [285,[288][289][290][291]. Mutations at position 177 have also been isolated upon selection for growth on sucrose [287].…”

Lactose permease mutants which transport (malto)-oligosaccharides

“…From the DNA sequence, the protein is predicted to contain 417 amino acids with a resulting molecular weight of 46,504. Secondary-structure models are consistent with the idea that the lactose permease contains 12 transmembrane segments that traverse the lipid bilayer in an a-helical conformation (8,14,22).In an attempt to obtain information concerning the molecular architecture of the sugar-binding site within the lactose permease, previous studies have been aimed at the selection and identification of lactose permease mutants which have an alteration in their sugar recognition properties (5,6,9,16,18,23,26). The rationale behind these experiments is that sugar specificity mutations will cause discrete alterations at the sugar-binding domain.…”

Structural features of the uniporter/symporter/antiporter superfamily

“…One way to explain the variability seen among potential channel-lining domains would be that different groups within the superfamily utilize different transmembrane domains as a hydrophilic surface for solute binding. In the case of the lactose permease, most sugar specificity mutants have been located on transmembrane domains in the second half of the protein (Brooker & Wilson, 1985;Markgraf et al, 1985;Collins et al, 1989;Franco et al, 1989). However, other families may use the first half, or combinations of the first and second half, to form a solute recognition site.…”