Journal: J Virol / Year: 2017 Title: Beta-Propiolactone Inactivation of Coxsackievirus A16 Induces Structural Alteration and Surface Modification of Viral Capsids. Authors: Chen Fan / Xiaohua Ye / Zhiqiang Ku / Liangliang Kong / Qingwei Liu / Cong Xu / Yao Cong / Zhong Huang / Abstract: Beta-propiolactone (BPL) is an inactivating agent that is widely used in the vaccine industry. However, its effects on vaccine protein antigens and its mechanisms of action remain poorly understood. ...Beta-propiolactone (BPL) is an inactivating agent that is widely used in the vaccine industry. However, its effects on vaccine protein antigens and its mechanisms of action remain poorly understood. Here we present cryo-electron microscopy (cryo-EM) structures of BPL-treated coxsackievirus A16 (CVA16) mature virions and procapsids at resolutions of 3.9 Å and 6.5 Å, respectively. Notably, both particles were found to adopt an expanded conformation resembling the 135S-like uncoating intermediate, with characteristic features including an opened 2-fold channel, the externalization of the N terminus of VP1 capsid protein, and the absence of pocket factor. However, major neutralizing epitopes are very well preserved on these particles. Further biochemical analyses revealed that BPL treatment impairs the abilities of CVA16 particles to bind to the attachment receptor heparan sulfate and to a conformation-dependent monoclonal antibody in a BPL dose-dependent manner, indicating that BPL is able to modify surface-exposed amino acid residues. Taken together, our results demonstrate that BPL treatment may induce alteration of the overall structure and surface properties of a nonenveloped viral capsid, thus revealing a novel mode of action of BPL. Beta-propiolactone (BPL) is commonly used as an inactivating reagent to produce viral vaccines. It is recognized that BPL inactivates viral infectivity through modification of viral nucleic acids. However, its effect on viral proteins remains largely unknown. Here, we present high-resolution cryo-EM structures of BPL-treated coxsackievirus A16 (CVA16) mature virions and procapsids, which reveals an expanded overall conformation and characteristic features that are typical for the 135S-like uncoating intermediate. We further show that the BPL concentration affects the binding of inactivated CVA16 particles to their receptor/antibody. Thus, BPL treatment can alter the overall structure and surface properties of viral capsids, which may lead to antigenic and immunogenic variations. Our findings provide important information for future development of BPL-inactivated vaccines.
History
Deposition
Aug 12, 2016
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Header (metadata) release
Oct 12, 2016
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Map release
Feb 1, 2017
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Update
May 2, 2018
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Current status
May 2, 2018
Processing site: PDBj / Status: Released
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Structure visualization
Movie
Surface view with section colored by density value
Model: Quantifoil / Material: COPPER / Mesh: 200 / Support film - Material: CARBON / Support film - topology: CONTINUOUS / Pretreatment - Type: GLOW DISCHARGE
Vitrification
Cryogen name: ETHANE / Chamber humidity: 100 % / Chamber temperature: 120 K / Instrument: FEI VITROBOT MARK III / Details: blot for 2 seconds.
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Electron microscopy
Microscope
FEI TITAN KRIOS
Temperature
Min: 70.0 K / Max: 90.0 K
Specialist optics
Spherical aberration corrector: Microscope was modified with a Cs corrector
Image recording
Film or detector model: FEI FALCON II (4k x 4k) / Detector mode: INTEGRATING / Digitization - Frames/image: 3-18 / Number grids imaged: 1 / Number real images: 1350 / Average exposure time: 1.1 sec. / Average electron dose: 25.0 e/Å2 Details: Images were recorded on a Falcon II direct electron detector in the 18-frame movie mode.
Electron beam
Acceleration voltage: 300 kV / Electron source: FIELD EMISSION GUN
Software - Name: jspr Software - details: CTF fitting was automatically performed using fitctf2.py program in jspr Details: CTF fitting was automatically performed using fitctf2.py program in jspr
Startup model
Type of model: INSILICO MODEL In silico model: The data we performed the reference-free 2D analysis and initial model building utilizing EMAN2.1 Details: The data we performed the reference-free 2D analysis and initial model building utilizing EMAN2.1
Final reconstruction
Applied symmetry - Point group: I (icosahedral) / Algorithm: FOURIER SPACE / Resolution.type: BY AUTHOR / Resolution: 3.9 Å / Resolution method: FSC 0.143 CUT-OFF / Software - Name: jspr Details: In the 3D reconstruction process, the gold standard procedure was followed using jspr package Number images used: 25610
Initial angle assignment
Type: COMMON LINE
Final angle assignment
Type: PROJECTION MATCHING / Software - Name: jspr
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Atomic model buiding 1
Refinement
Protocol: RIGID BODY FIT
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