Experimental evolution of Rc-o319 sarbecovirus spike protein reveals limited ACE2 adaptability

Area of Science:

• Virology
• Evolutionary Biology
• Zoonotic Disease Research

Background:

• Bat sarbecoviruses are closely related to SARS-CoV-2 and can potentially infect humans.
• The viral spike protein's interaction with the host Angiotensin-Converting Enzyme 2 (ACE2) receptor is crucial for cross-species transmission.
• Understanding the evolvability of bat sarbecoviruses is key to assessing their pandemic potential.

Purpose of the Study:

• To investigate the ACE2 receptor usage and evolutionary adaptability of the Rc-o319 bat sarbecovirus spike protein.
• To assess the potential for the Rc-o319 spike protein to adapt to human ACE2 and evaluate zoonotic risk.

Main Methods:

• Utilized a recombinant vesicular stomatitis virus (VSV) system to study the Rc-o319 spike protein.
• Performed experimental evolution passages of the recombinant VSV under selective pressure for viral entry.
• Analyzed spike protein mutations and ACE2 receptor binding affinity.

Main Results:

• The Rc-o319 spike protein primarily used its natural host ACE2 (Rhinolophus cornutus) and showed limited binding to mouse ACE2.
• Experimental evolution rapidly optimized the Rc-o319 spike for entry via mouse ACE2 with a single mutation.
• Despite strong selective pressure, no variants capable of efficiently using human ACE2 were generated, indicating evolutionary constraints.

Conclusions:

• The Rc-o319 spike protein can easily adapt to permissive ACE2 receptors like mouse ACE2.
• Significant evolutionary barriers limit the adaptation of the Rc-o319 spike protein to human ACE2, suggesting a low risk of zoonotic transmission.
• Further investigation is needed to confirm potential ACE2-independent viral entry mechanisms in evolved variants.