2.2 Å resolution cryo-EM structure of β-galactosidase in complex with a cell-permeant inhibitor

Science. 2015 Jun 5;348(6239):1147-51. doi: 10.1126/science.aab1576. Epub 2015 May 7.


Cryo-electron microscopy (cryo-EM) is rapidly emerging as a powerful tool for protein structure determination at high resolution. Here we report the structure of a complex between Escherichia coli β-galactosidase and the cell-permeant inhibitor phenylethyl β-D-thiogalactopyranoside (PETG), determined by cryo-EM at an average resolution of ~2.2 angstroms (Å). Besides the PETG ligand, we identified densities in the map for ~800 water molecules and for magnesium and sodium ions. Although it is likely that continued advances in detector technology may further enhance resolution, our findings demonstrate that preparation of specimens of adequate quality and intrinsic protein flexibility, rather than imaging or image-processing technologies, now represent the major bottlenecks to routinely achieving resolutions close to 2 Å using single-particle cryo-EM.

Publication types

  • Research Support, N.I.H., Intramural

MeSH terms

  • Catalytic Domain
  • Cryoelectron Microscopy
  • Crystallography, X-Ray
  • Escherichia coli / enzymology*
  • Escherichia coli Proteins / chemistry*
  • Thiogalactosides / chemistry*
  • Water / chemistry
  • beta-Galactosidase / chemistry*


  • Escherichia coli Proteins
  • Thiogalactosides
  • Water
  • phenylethylthio-beta-galactopyranoside
  • beta-Galactosidase

Associated data

  • PDB/5A1A