From Binding to Catalysis: Emergence of a Rudimentary Enzyme Conferring Intrinsic Antibiotic Resistance

Area of Science:

• Enzymology
• Evolutionary Biology
• Structural Biology

Background:

• Type B dihydrofolate reductases (DfrB) are distinct from FolA enzymes and implicated in antibiotic resistance.
• DfrB enzymes utilize the Src Homology 3 (SH3) fold, typically a protein-binding module, not known for catalysis.
• Understanding DfrB offers insights into the emergence of enzymatic activity from non-catalytic protein domains.

Purpose of the Study:

• To investigate the evolutionary origins of enzymatic activity in DfrB.
• To elucidate the relationship between DfrB structure, homotetramerization, and catalytic function.
• To determine if DfrB evolved its catalytic capacity in response to antibiotic pressure.

Main Methods:

• Comparative analysis of DfrB homologs to track evolutionary conservation.
• Experimental and computational methods to study enzyme structure-function relationships.
• Assessing the impact of homotetramerization on substrate binding and catalysis.

Main Results:

• No active-site residues are conserved across catalytically active DfrB homologs.
• Homotetramerization of DfrB forms a tunnel with positive electrostatic potential, correlating strongly with catalytic activity.
• DfrB's catalytic activity is not linked to the antibiotic resistance it confers, suggesting a pre-existing capacity.

Conclusions:

• Catalytic activity in DfrB emerged from the homotetramerization of an ancestral binding domain.
• The evolution of DfrB demonstrates how rudimentary catalysis can arise opportunistically.
• Pathogenic bacteria have recently recruited these evolved DfrB enzymes for antibiotic resistance.