Acknowledgments
We thank M. Dixon and M. Gowland-Pryde for supporting our work on this project during the difficulties arising from the pandemic and G. Ould for critical reading of the manuscript. Funding: This work was funded by the International AIDS Vaccine Initiative, Bill and Melinda Gates Foundation through the Collaboration for AIDS Vaccine Discovery (OPP1084519 and 1196345 to M.C.), the NIAID (R01-AI127521 to J.S.M.), and the Scripps Consortium for HIV Vaccine Development (CHAVD) (AI144462 to M.C.). M.C. is a Supernumerary Fellow of Oriel College, Oxford, and professor adjunct at Scripps Research, CA. Author contributions: Y.W. and J.D.A. performed mass spectrometry experiments and analyzed data. Y.W. built glycosylated models. J.S.M. and M.C. supervised experiments. Y.W., J.D.A., and D.W. expressed and purified proteins. Y.W., J.D.A., and M.C. wrote the manuscript with input from all authors. Competing interests: J.S.M. is an inventor on U.S. patent application no. 62/412,703 (“Prefusion Coronavirus Spike Proteins and Their Use”), and D.W. and J.S.M. are inventors on U.S. patent application no. 62/972,886 (“2019-nCoV Vaccine”). Data and materials availability: Mass spectrometry raw files have been deposited in the MassIVE proteomics database (37). The plasmid is available from J.S.M. under a material transfer agreement with The University of Texas at Austin. This work is licensed under a Creative Commons Attribution 4.0 International (CC BY 4.0) license, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. To view a copy of this license, visit https://creativecommons.org/licenses/by/4.0/. This license does not apply to figures, photos, artwork, or other content included in the article that is credited to a third party; obtain authorization from the rights holder before using such material.

Supplementary Materials
science.sciencemag.org/content/369/6501/330/suppl/DC1
Materials and Methods
Figs. S1 to S4
Tables S1 and S2
References (38, 39)
MDAR Reproducibility Checklist
Data S1

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