title: Structural and functional studies on the extracellular domain of BST2/tetherin in reduced and oxidized conformations.
abstract: HIV-1 and other enveloped viruses can be restricted by a host cellular protein called BST2/tetherin that prevents release of budded viruses from the cell surface. Mature BST2 contains a small cytosolic region, a predicted transmembrane helix, and an extracellular domain with a C-terminal GPI anchor. To advance understanding of BST2 function, we have determined a 2.6 Å crystal structure of the extracellular domain of the bacterially expressed recombinant human protein, residues 47-152, under reducing conditions. The structure forms a single long helix that associates as a parallel dimeric coiled coil over its C-terminal two-thirds, while the N-terminal third forms an antiparallel four-helix bundle with another dimer, creating a global tetramer. We also report the 3.45 Å resolution structure of BST2(51-151) prepared by expression as a secreted protein in HEK293T cells. This oxidized construct forms a dimer in the crystal that is superimposable with the reduced protein over the C-terminal two-thirds of the molecule, and its N terminus suggests pronounced flexibility. Hydrodynamic data demonstrated that BST2 formed a stable tetramer under reducing conditions and a dimer when oxidized to form disulfide bonds. A mutation that selectively disrupted the tetramer (L70D) increased protein expression modestly but only reduced antiviral activity by approximately threefold. Our data raise the possibility that BST2 may function as a tetramer at some stage, such as during trafficking, and strongly support a model in which the primary functional state of BST2 is a parallel disulfide-bound coiled coil that displays flexibility toward its N terminus.
authors.affiliation: Department of Biochemistry, University of Utah School of Medicine, Salt Lake City, UT 84112-5650, USA.
authors.forename: Heidi L
authors.initials: HL
authors.lastname: Schubert
authors.forename: Qianting
authors.initials: Q
authors.lastname: Zhai
authors.forename: Virginie
authors.initials: V
authors.lastname: Sandrin
authors.forename: Debra M
authors.initials: DM
authors.lastname: Eckert
authors.forename: Mitla
authors.initials: M
authors.lastname: Garcia-Maya
authors.forename: Louise
authors.initials: L
authors.lastname: Saul
authors.forename: Wesley I
authors.initials: WI
authors.lastname: Sundquist
authors.forename: Roberto A
authors.initials: RA
authors.lastname: Steiner
authors.forename: Christopher P
authors.initials: CP
authors.lastname: Hill
mesh_terms: D015703:Antigens, CD / Q000737:chemistry / Q000378:metabolism*; D001704:Biopolymers / Q000737:chemistry; D018360:Crystallography, X-Ray; D058851:GPI-Linked Proteins / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D010084:Oxidation-Reduction; D011487:Protein Conformation; D013329:Structure-Activity Relationship; D000074010:Bone Marrow Stromal Antigen 2
chemical_list: D015703:Antigens, CD; D001704:Biopolymers; D058851:GPI-Linked Proteins; C094572:BST2 protein, human; D000074010:Bone Marrow Stromal Antigen 2