Selection Analysis Identifies Clusters of Unusual Mutational Changes in Omicron Lineage BA.1 That Likely Impact Spike...

Area of Science:

• Virology
• Genomics
• Molecular Biology

Background:

• The Omicron variant of SARS-CoV-2 possesses numerous mutations in its Spike (S) gene.
• Thirteen of these mutations are rare in previous SARS-CoV-2 sequences and cluster in functionally critical regions.

Purpose of the Study:

• To investigate the evolutionary origins and functional impact of the unique mutations in the Omicron S-gene.
• To understand how these mutations cooperatively alter Spike protein function and contribute to Omicron's fitness.

Main Methods:

• Analysis of mutation rarity in intrapatient sequencing reads.
• Selection pattern analysis at codon sites across SARS-CoV-2 and related sarbecoviruses.
• In silico prediction of fitness costs and adaptive alterations.

Main Results:

• Prior to Omicron's emergence, the 13 rare mutations were predicted to decrease viral fitness.
• These mutations cluster in regions affecting Spike trimerization, ACE2 receptor binding, and membrane fusion.
• The mutations likely interact synergistically to mitigate individual fitness costs and adapt Spike function.

Conclusions:

• The Omicron S-gene mutations represent a complex, adaptive constellation that confers epidemic growth advantages.
• Understanding the assembly of these mutations and the undetected early stages of Omicron evolution is critical.