One of the essential factors the COVID-19 virus needs to enter a host is a receptor on a human cell — a place where the universally recognized spike protein can latch onto the cell surface, pierce it, disgorge its infectious contents, and replicate.
Without a receptor, there is no replication. Without replication, there is no infection.
Researchers in Princeton University’s Department of Chemistry and the Department of Molecular Biology have used a cellular mapping technology called µMap, introduced just two years ago by the MacMillan Lab, to uncover eight previously unknown entry points of interest for the spike protein.
Four of them, researchers found, are functionally important for viral entry.
The research was published earlier this month in the Journal of the American Chemical Society (JACS). It could expand the suite of tools used to fight the virus, particularly as it mutates and evolves ways to evade vaccines.
The collaborative project was begun at the height of pandemic uncertainty two years ago under Alexander Ploss, a leading virologist and professor of molecular biology, and David MacMillan, the James S. McDonnell Distinguished University Professor and a Nobel laureate in chemistry.
Scientists have known since the SARS-CoV-1 virus appeared in 2003 that its primary viral entry receptor was an enzyme called angiotensin-converting enzyme 2, or ACE2. This enzyme was confirmed in 2020 as the same receptor for SARS-CoV-2, the virus that causes COVID-19.
But the Princeton project started with the assumption that ACE2 was not the only story.
“We did know that there are certain host molecules that this virus absolutely depends on to enter into lung cells to cause the infection, and one of these molecules is called ACE2,” said Ploss. “So we basically said, okay, let’s see if there’s more out there. We looked for immediate binders.
“But as you can imagine, the entry process is complex. The virus attaches to something and then it still has to pass through the cell membrane to get into a cell, and along this way it may interact with other host factors. I don’t want to say everything is dictated by viral entry. Obviously, there are a number of equally essential processes within the cell after the virus has entered that can influence disease severity.
“But it’s obviously the first key step. If the virus can’t get in, it’s game over.”
Steve Knutson, a co-author on the paper and a postdoctoral research fellow in the MacMillan Lab, added: “While the discovery of ACE2 as the major receptor was a huge milestone, it certainly doesn’t tell the whole story of COVID pathology. Biology can be inherently promiscuous, and we guessed correctly that the SARS-CoV-2 spike protein interacts with multiple host cell proteins for entry.”
He added that investigations like this one are a “perfect” research fit for the µMap technology.