Retrovirus envelope protein complex structure in situ studied by cryo-electron tomography.
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.
Förster
Friedrich
F
Abteilung für Molekulare Strukturbiologie, Max-Planck-Institut für Biochemie, Am Klopferspitz 18, D-82152 Martinsried, Germany. foerster@biochem.mpg.de
Medalia
Ohad
O
Zauberman
Nathan
N
Baumeister
Wolfgang
W
Fass
Deborah
D
D000465:Algorithms; D020285:Cryoelectron Microscopy / Q000379:methods*; D007091:Image Processing, Computer-Assisted; D008979:Moloney murine leukemia virus / Q000648:ultrastructure*; D011487:Protein Conformation; D014054:Tomography / Q000379:methods; D014759:Viral Envelope Proteins / Q000648:ultrastructure*
D014759:Viral Envelope Proteins