Retrovirus envelope protein complex structure in situ studied by cryo-electron tomography

Proc Natl Acad Sci U S A. 2005 Mar 29;102(13):4729-34. doi: 10.1073/pnas.0409178102. Epub 2005 Mar 17.


We used cryo-electron tomography in conjunction with single-particle averaging techniques to study the structures of frozen-hydrated envelope glycoprotein (Env) complexes on intact Moloney murine leukemia retrovirus particles. Cryo-electron tomography allows 3D imaging of viruses in toto at a resolution sufficient to locate individual macromolecules, and local averaging of abundant complexes substantially improves the resolution. The averaging of repetitive features in electron tomograms is hampered by a low signal-to-noise ratio and anisotropic resolution, which results from the "missing-wedge" effect. We developed an iterative 3D averaging algorithm that compensates for this effect and used it to determine the trimeric structure of Env to a resolution of 2.7 nm, at which individual domains can be resolved. Strikingly, the 3D reconstruction is shaped like a tripod in which the trimer penetrates the membrane at three distinct locations approximately 4.5 nm apart from one another. The Env reconstruction allows tentative docking of the x-ray crystal structure of the receptor-binding domain. This study thus provides 3D structural information regarding the prefusion conformation of an intact unstained retrovirus surface protein.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Algorithms*
  • Cryoelectron Microscopy / methods*
  • Image Processing, Computer-Assisted
  • Moloney murine leukemia virus / ultrastructure*
  • Protein Conformation
  • Tomography / methods
  • Viral Envelope Proteins / ultrastructure*


  • Viral Envelope Proteins