Disease relevance of lacY

• In vitro and in vivo products of E. coli lactose permease gene are identical [1].

High impact information on lacY

• Recent mutagenesis studies of sugar transporters within the framework of tenable models for the distantly related lactose permease argue that this model is a good paradigm for other members of the major facilitator superfamily [2].
• Inhibition of beta-galactosidase activity in E. coli ML-35, a strain lacking functional lactose permease, is complex and also depends upon the identity of the oxidant [3].
• Here, we present two novel ligand-free X-ray structures of the lactose permease (LacY) of Escherichia coli determined at acidic and neutral pH, and propose a model for the mechanism of coupling between lactose and H+ translocation [4].
• Integration of biochemical and biophysical data on the lactose permease of Escherichia coli has culminated in a molecular model that predicts substrate-protein proximities which include interaction of a hydroxyl group in the galactopyranosyl ring with Glu269 [5].
• To address the role of phospholipids in the topological organization of polytopic membrane proteins, the function and assembly of lactose permease (LacY) was studied in mutants of Escherichia coli lacking phosphatidylethanolamine (PE) [6].

Chemical compound and disease context of lacY

• Previously we presented evidence that phosphatidylethanolamine (PE) acts as a molecular chaperone in the folding of the polytopic membrane protein lactose permease (LacY) of Escherichia coli [7].
• The lactose permease of Escherichia coli was labeled with eosinyl-maleimide, reconstituted into vesicles of dimyristoylphosphatidylcholine and subjected to time-dependent phosphorescence anisotropy measurements in order to determine the rotational diffusion coefficient [8].
• In a functional lactose permease mutant from Escherichia coli (LacY) devoid of native Cys residues, almost every residue was replaced individually with Cys and tested for reactivity with the permeant alkylating agent N-ethylmaleimide in right-side-out membrane vesicles [9].
• Deduction of consensus binding sequences on proteins that bind IIAGlc of the phosphoenolpyruvate:sugar phosphotransferase system by cysteine scanning mutagenesis of Escherichia coli lactose permease [10].
• Changing the lactose permease of Escherichia coli into a galactose-specific symporter [11].

Biological context of lacY

• Determination of lacZ and lacY mRNA levels revealed a pattern of reduction that was similar to the Lac-proteins, indicating a relation between translation inhibition and mRNA degradation as a response to antisense PNA treatment [12].
• Phospholipid-assisted protein folding: phosphatidylethanolamine is required at a late step of the conformational maturation of the polytopic membrane protein lactose permease [7].
• Conformational flexibility at the substrate binding site in the lactose permease of Escherichia coli [13].
• A mechanistic model for lactose/H(+) symport via the lactose permease of Escherichia coli proposed recently indicates that the permease must be protonated to bind ligand with high affinity [14].
• Topology of allosteric regulation of lactose permease [15].

Anatomical context of lacY

• Because of the extensive aggregation of lactose permease synthesized in the absence of membranes, only low amounts originating from the soluble enzyme pool integrated posttranslationally into the membrane vesicles [16].
• The lactose permease of Escherichia coli catalyzes coupled translocation of galactosides and H(+) across the cell membrane [17].
• Epitope 4B1 is readily detectable in spheroplasts and right-side-out membrane vesicles from PE-containing but not from PE-deficient cells expressing lactose permease [18].
• This is interpreted as evidence for two different conformations of lactose permease, one with the binding site open to the cytoplasm and closed to the periplasm and vice versa for the other state [19].
• From similar experiments with N-terminal segments of lactose permease, we estimate that at most a polypeptide of 120 amino acid residues emerging from the ribosome is needed to target the nascent chain to the lipid bilayer and to mediate attachment of the ribosome to the membrane during elongation [20].

Associations of lacY with chemical compounds

• Moreover, membrane vesicles when present cotranslationally during synthesis of lactose permease, acquired the capability to accumulate lactose, strongly suggesting a correct in vitro assembly of the enzyme [16].
• Site-directed N-ethylmaleimide labeling was studied with Glu-126 and/or Arg-144 mutants in lactose permease containing a single, native Cys residue at position 148 in the substrate-binding site [21].
• Thus, three individual cysteine residues were introduced into putative helix IV of a lactose permease mutant devoid of native cysteine residues containing a high-affinity divalent metal ion binding site in the form of six contiguous histidine residues in the periplasmic loop between helices III and IV [22].
• Regulation of lactose permease activity by the phosphoenolpyruvate:sugar phosphotransferase system: evidence for direct binding of the glucose-specific enzyme III to the lactose permease [23].
• Treatment of lactose permease with N-ethylmaleimide, which blocks ligand binding and transport by alkylating Cys-148, also blocks enzyme IIAglc binding [15].

Regulatory relationships of lacY

• Finally, lactose permease activity was 50% of that in control cells containing the same levels of beta-galactosidase, and the lactose permease activity in the IIIGlc overproducer was reduced to an extremely low level in the presence of methyl alpha-glucoside [24].

Analytical, diagnostic and therapeutic context of lacY

• The structure of the lactose permease derived from Raman spectroscopy and prediction methods [25].
• By applying an established crystallization protocol for the lactose permease (LacY) of Escherichia coli, a systematic study of the effect of phospholipids (PL) on crystallization of LacY was undertaken [26].
• Isothermal titration calorimetry has been applied to characterize the thermodynamics of ligand binding to wild-type lactose permease (LacY) and a mutant (C154G) that strongly favors an inward facing conformation [27].
• Lactose permease from PE-containing membranes, but not from PE-deficient membranes, subjected to sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis and Western blot analysis is also recognized by mAb 4B1 [18].
• Sequence alignment and homology threading reveals prokaryotic and eukaryotic proteins similar to lactose permease [28].

References