title: Native structure of a retroviral envelope protein and its conformational change upon interaction with the target cell.
abstract: Enveloped viruses enter their host cells by membrane fusion. The process of attachment and fusion in retroviruses is mediated by a single viral envelope glycoprotein (Env). Conformational changes of Env in the course of fusion are a focus of intense studies. Here we provide further insight into the changes occurring in retroviral Env during its initial interaction with the cell, employing murine leukemia virus (MLV) as model system. We first determined the structure of both natively membrane anchored MLV Env and MLV Env tagged with YFP in the proline rich region (PRR) by electron cryo tomography (cET) and sub-volume averaging. At a resolution of ∼20Å, native MLV Env presents as a hollow trimer (height ∼85Å, diameter ∼120Å) composed of step-shaped protomers. The major difference to the YFP-tagged protein was in regions outside of the central trimer. Next, we focused on elucidating the changes in MLV Env upon interaction with a host cell. Virus interaction with the plasma membrane occurred over a large surface and Env clustering on the binding site was observed. Sub-volume averaging did yield a low-resolution structure of Env interacting with the cell, which had lost its threefold symmetry and was elongated by ∼35Å in comparison to the unbound protein. This indicates a major rearrangement of Env upon host cell binding. At the site of virus interaction, the otherwise clearly defined bilayer structure of the host cell plasma membrane was much less evident, indicative of integral membrane protein accumulation and/or a change in membrane lipid composition.
authors.affiliation: Division of Structural Biology, Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford OX3 7BN, UK; Institute of Virology, University of Veterinary Medicine, Vienna, Austria.
authors.forename: Christiane
authors.initials: C
authors.lastname: Riedel
authors.affiliation: Division of Structural Biology, Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford OX3 7BN, UK.
authors.forename: Daven
authors.initials: D
authors.lastname: Vasishtan
authors.affiliation: Division of Structural Biology, Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford OX3 7BN, UK.
authors.forename: C Alistair
authors.initials: CA
authors.lastname: Siebert
authors.affiliation: Division of Structural Biology, Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford OX3 7BN, UK.
authors.forename: Cathy
authors.initials: C
authors.lastname: Whittle
authors.affiliation: Department of Life Sciences and Engineering, University of Applied Sciences Bingen, Germany.
authors.forename: Maik J
authors.initials: MJ
authors.lastname: Lehmann
authors.affiliation: Department of Microbial Pathogenesis, Yale University School of Medicine, New Haven, CT, USA.
authors.forename: Walther
authors.initials: W
authors.lastname: Mothes
authors.affiliation: Division of Structural Biology, Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford OX3 7BN, UK. Electronic address: kay@strubi.ox.ac.uk.
authors.forename: Kay
authors.initials: K
authors.lastname: Grünewald
mesh_terms: D001665:Binding Sites; D020285:Cryoelectron Microscopy / Q000379:methods*; D009052:Leukemia Virus, Murine / Q000502:physiology / Q000648:ultrastructure*; D011487:Protein Conformation; D014759:Viral Envelope Proteins / Q000648:ultrastructure*
chemical_list: D014759:Viral Envelope Proteins
keywords: Electron cryo tomography; Env; Murine leukemia virus; Retroviridae; Sub-volume averaging; Virus entry