Pervasive Pairwise Intragenic Epistasis among Sequential Mutations in TEM-1 β-Lactamase

Area of Science:

• Molecular Biology
• Biochemistry
• Evolutionary Genetics

Background:

• Intragenic epistasis, interactions between mutations within a gene, is crucial for understanding fitness landscapes.
• Previous research has not fully elucidated the prevalence and patterns of intragenic epistasis.

Purpose of the Study:

• To investigate the prevalence and patterns of epistatic interactions between sequential mutations in TEM-1 beta-lactamase.
• To determine whether these interactions are specific or nonspecific.

Main Methods:

• Measured fitness effects of approximately 12,000 pairs of consecutive amino acid substitutions in TEM-1 beta-lactamase.
• Calculated epistasis for over 8000 mutation pairs using data from single amino acid substitutions.

Main Results:

• Discovered widespread negative epistasis, particularly in beta-strands.
• Observed a high frequency of negative sign epistasis among individually beneficial mutations (52% negative vs. 6.8% positive).
• Found that buried residues experience more negative epistasis than surface-exposed residues, with notable hotspots for positive epistasis.

Conclusions:

• This systematic examination of pairwise epistasis in TEM-1 beta-lactamase provides novel insights into intragenic interactions.
• The findings highlight the significant role of negative epistasis in shaping protein evolution and function.