Evolution of a new enzymatic function by recombination within a gene.

Area of Science:

• Biochemistry
• Molecular Biology
• Evolutionary Biology

Background:

• The ebgA gene in Escherichia coli encodes beta-galactosidase (ebg), an enzyme involved in lactose hydrolysis.
• Mutations in ebgA lead to evolved ebg enzymes with altered substrate specificities.

Purpose of the Study:

• To investigate the combined effect of class I and class II ebgA mutations on enzyme specificity.
• To explore the evolution of galactosylarabinose utilization by the ebg enzyme.

Main Methods:

• Analysis of Escherichia coli ebgA mutants with class I and class II mutations.
• Characterization of enzyme activity and substrate specificity.
• Investigating evolution via spontaneous mutation and intragenic recombination.

Main Results:

• Class I ebgA mutants hydrolyze lactose; Class II mutants hydrolyze lactose and lactulose.
• Combined class I and class II mutations confer specificity for galactosylarabinose.
• Galactosylarabinose utilization evolves through sequential mutations or intragenic recombination.

Conclusions:

• The ebgA gene's class I and class II mutation sites are approximately 1 kilobase apart.
• Evolutionary pathways, including recombination, can lead to novel metabolic functions.
• Understanding enzyme evolution provides insights into metabolic innovation.