SARS CoV-2 spike adopts distinct conformational ensembles in situ
Engineered recombinant Spike (S) has been invaluable for determining S structure and dynamics and is the basis for the design of most prevalent vaccines. While these vaccines have been highly efficacious for short-term protection from infection, protection waned with the emergence of variants (alpha through omicron). Here we report differences in conformational dynamics between native, membrane-embedded full-length S and recombinant S. Our virus-like particle (VLP) model mimics the native SARS CoV-2 virion by displaying S assembled with auxiliary E, M, and N proteins in a native membrane environment that captures the entirety of quaternary interactions mediated by S. Display of S on VLP obviates the requirement for stabilizing modifications that have been engineered into recombinant S for enhanced expression and solubility. Amide hydrogen/deuterium exchange mass spectrometry (HDXMS) reveals altered interprotomer contacts in VLP S trimers attributable to the presence of auxiliary proteins, membrane anchoring, and lack of engineered modifications. Our results reveal decreased dynamics in the S2 subunit and at sites spanning interprotomer contacts in VLP S with minimal differences in the N-terminal domain (NTD) and receptor binding domain (RBD). This carries implications for display of epitopes beyond NTD and RBD. In summary, despite affording efficient structural characterization, recombinant S distorts the intrinsic conformational ensemble of native S displayed on the virus surface.