ジャーナル: Proc Natl Acad Sci U S A / 年: 2014 タイトル: Furin cleavage of the Moloney murine leukemia virus Env precursor reorganizes the spike structure. 著者: Mathilda Sjöberg / Shang-Rung Wu / Robin Löving / Kimmo Rantalainen / Birgitta Lindqvist / Henrik Garoff / 要旨: The trimeric Moloney murine leukemia virus Env protein matures by two proteolytic cleavages. First, furin cleaves the Env precursor into the surface (SU) and transmembrane (TM) subunits in the cell ...The trimeric Moloney murine leukemia virus Env protein matures by two proteolytic cleavages. First, furin cleaves the Env precursor into the surface (SU) and transmembrane (TM) subunits in the cell and then the viral protease cleaves the R-peptide from TM in new virus. Here we analyzed the structure of the furin precursor, by cryoelectron microscopy. We transfected 293T cells with a furin cleavage site provirus mutant, R466G/K468G, and produced the virus in the presence of amprenavir to also inhibit the R-peptide cleavage. Although Env incorporation into particles was inhibited, enough precursor could be isolated and analyzed by cryoelectron microscopy to yield a 3D structure at 22 Å resolution. This showed an open cage-like structure like that of the R-peptide precursor and the mature Env described before. However, the middle protrusion of the protomeric unit, so prominently pointing out from the side of the more mature forms of the Env, was absent. Instead, there was extra density in the top protrusion. This suggested that the C-terminal SU domain was associated alongside the receptor binding N-terminal SU domain in the furin precursor. This was supported by mapping with a SU C-terminal domain-specific antigen binding fragment. We concluded that furin cleavage not only separates the subunits and liberates the fusion peptide at the end of TM but also allows the C-terminal domain to relocate into a peripheral position. This conformational change might explain how the C-terminal domain of SU gains the potential to undergo disulfide isomerization, an event that facilitates membrane fusion.
pH: 7.4 / 詳細: 50 mM HEPES, 100 mM NaCl, 1.8 mM CaCl2, pH 7.4
グリッド
詳細: 400 mesh holey carbon grid, glow discharged
凍結
凍結剤: ETHANE / チャンバー内湿度: 90 % / チャンバー内温度: 77 K / 装置: FEI VITROBOT MARK II 手法: Blotted for 3 seconds before plunging in liquid ethane, followed by transfer into liquid nitrogen.
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電子顕微鏡法
顕微鏡
JEOL 2100F
温度
最低: 93 K / 最高: 96 K / 平均: 95 K
アライメント法
Legacy - 非点収差: Objective lens astigmatism was corrected using online FFT.
The particles were selected using a semi-automatic selection program in EMAN.
CTF補正
詳細: Each particle
最終 再構成
アルゴリズム: OTHER / 解像度のタイプ: BY AUTHOR / 解像度: 23.0 Å / 解像度の算出法: OTHER / ソフトウェア - 名称: EMAN1, EMAN2 詳細: Final maps were calculated from seven averaged datasets. The particles were selected using an automatic selection program. Damaged particles were removed after visual inspection. 使用した粒子像数: 3825
The atomic model for the Mo-RBD was obtained using the atomic structure of the highly homologous F-RBD (Fass et al, 1997) (PDB ID 1AOL) and the SWISS-MODEL protein structure homology-modeling server (accessible through the ExPASy web server).