Crystal structure of E. coli lactose permease G46W,G262W bound to sugar

Experimental Data Snapshot

  • Resolution: 3.50 Å
  • R-Value Free: 0.293 
  • R-Value Work: 0.257 
  • R-Value Observed: 0.258 

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This is version 3.1 of the entry. See complete history


Structure of sugar-bound LacY.

Kumar, H.Kasho, V.Smirnova, I.Finer-Moore, J.S.Kaback, H.R.Stroud, R.M.

(2014) Proc Natl Acad Sci U S A 111: 1784-1788

  • DOI: https://doi.org/10.1073/pnas.1324141111
  • Primary Citation of Related Structures:  

  • PubMed Abstract: 

    Here we describe the X-ray crystal structure of a double-Trp mutant (Gly46→Trp/Gly262→Trp) of the lactose permease of Escherichia coli (LacY) with a bound, high-affinity lactose analog. Although thought to be arrested in an open-outward conformation, the structure is almost occluded and is partially open to the periplasmic side; the cytoplasmic side is tightly sealed. Surprisingly, the opening on the periplasmic side is sufficiently narrow that sugar cannot get in or out of the binding site. Clearly defined density for a bound sugar is observed at the apex of the almost occluded cavity in the middle of the protein, and the side chains shown to ligate the galactopyranoside strongly confirm more than two decades of biochemical and spectroscopic findings. Comparison of the current structure with a previous structure of LacY with a covalently bound inactivator suggests that the galactopyranoside must be fully ligated to induce an occluded conformation. We conclude that protonated LacY binds D-galactopyranosides specifically, inducing an occluded state that can open to either side of the membrane.

  • Organizational Affiliation

    Department of Biochemistry and Biophysics, University of California, San Francisco, CA 94158.

Find similar proteins by:  (by identity cutoff)  |  3D Structure
Entity ID: 1
MoleculeChains Sequence LengthOrganismDetailsImage
Lactose/galactose transporter
A, B
417Escherichia coli str. K-12 substr. DH10BMutation(s): 2 
Gene Names: lacYECDH10B_1356
Entity Groups  
Sequence Clusters30% Identity50% Identity70% Identity90% Identity95% Identity100% Identity
Sequence Annotations
  • Reference Sequence


Entity ID: 2
MoleculeChains Length2D Diagram Glycosylation3D Interactions
beta-D-galactopyranose-(1-1)-1-thio-beta-D-galactopyranoseC [auth E],
D [auth F]
Biologically Interesting Molecules (External Reference) 1 Unique
Experimental Data & Validation

Experimental Data

  • Resolution: 3.50 Å
  • R-Value Free: 0.293 
  • R-Value Work: 0.257 
  • R-Value Observed: 0.258 
  • Space Group: C 2 2 21
Unit Cell:
Length ( Å )Angle ( ˚ )
a = 101.56α = 90
b = 121.94β = 90
c = 264.01γ = 90
Software Package:
Software NamePurpose
XDSdata reduction
XSCALEdata scaling

Structure Validation

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Entry History 

Deposition Data

Revision History  (Full details and data files)

  • Version 1.0: 2014-01-29
    Type: Initial release
  • Version 1.1: 2014-02-26
    Changes: Database references
  • Version 1.2: 2017-11-22
    Changes: Refinement description
  • Version 1.3: 2019-07-17
    Changes: Data collection, Refinement description
  • Version 2.0: 2020-07-29
    Type: Remediation
    Reason: Carbohydrate remediation
    Changes: Atomic model, Data collection, Database references, Derived calculations, Non-polymer description, Structure summary
  • Version 3.0: 2020-08-12
    Changes: Atomic model, Data collection, Derived calculations, Structure summary
  • Version 3.1: 2023-09-20
    Changes: Data collection, Database references, Refinement description