SARS-CoV-2 XBB.1.5 spike glycoprotein (S protein) (S protein)

The SARS-CoV-2 XBB.1.5 spike glycoprotein is a class I viral fusion protein that mediates the entry of the SARS-CoV-2 virus into host cells (Wikipedia, https://en.wikipedia.org/wiki/Coronavirus_spike_protein). It consists of two subunits, S1 and S2; the S1 subunit contains the receptor-binding domain (RBD) that attaches to the human angiotensin-converting enzyme 2 (ACE2) receptor, while the S2 subunit facilitates the fusion of the viral and cellular membranes (NIH, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10420017/). The XBB.1.5 variant, nicknamed "Kraken," is a recombinant of two BA.2 sublineages and is characterized by the S486P mutation, which significantly enhances its binding affinity for ACE2 and contributes to its high transmissibility and immune evasion (NIH, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10420017/). This protein is the primary target for COVID-19 vaccines, including the updated 2023-2024 monovalent formulations from Pfizer-BioNTech, Moderna, and Novavax, as well as monoclonal antibodies like pemivibart (CDC, https://www.cdc.gov/mmwr/volumes/73/wr/mm7304a2.htm; Invivyd, https://investors.invivyd.com/news-releases/news-release-details/invivyd-provides-detailed-virology-data-supporting-previously). However, the rapid evolution of the spike protein poses a continuous challenge for therapeutic efficacy, as new mutations can lead to reduced neutralization by existing antibodies and vaccines (NIH, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10943614/).

Other names

Spike proteinS proteinS glycoproteinSurface glycoproteinOmicron XBB.1.5 spikeKraken variant spike

Neutralization of viral entry by blocking the interaction between the spike protein's receptor-binding domain (RBD) and the host cell's angiotensin-converting enzyme 2 (ACE2) receptor.