Primordial-like enzymes from bacteria with reduced genomes

Area of Science:

• Biochemistry
• Enzymology
• Microbial Genetics

Background:

• Multifunctional enzymes with promiscuous activities are often considered relics of early life.
• Few enzymes catalyze multiple physiologically relevant reactions using a single active site.
• Escherichia coli cystathionine β-lyase (CBL) exhibits promiscuous alanine racemase (ALR) activity.

Purpose of the Study:

• Investigate multifunctional CBL/ALR enzymes in bacteria with reduced genomes.
• Determine the physiological relevance of CBL activity in these organisms.
• Characterize the enzymatic functions of CBL from Pelagibacter ubique, Wolbachia endosymbiont of Drosophila melanogaster (wMel), and Thermotoga maritima.

Main Methods:

• Genomic analysis to identify bacteria lacking alr but possessing metC.
• Biochemical characterization of CBL enzymes from selected bacterial species.
• Enzyme activity assays to assess both CBL and ALR functions.

Main Results:

• Several bacteria with reduced genomes utilize CBL enzymes lacking alanine racemase (ALR).
• CBL enzymes from P. ubique, wMel, and T. maritima function as multifunctional CBL/ALR.
• CBL activity is not essential in these bacteria; wMel and T. maritima CBLs are physiologically bi-functional alanine/glutamate racemases.
• These enzymes exhibit lower activity but are sufficient for physiological needs.

Conclusions:

• Primordial-like, multifunctional enzymes play a significant role in the biochemistry of streamlined microorganisms.
• The adaptive strategy of genome streamlining involves utilizing less active, yet sufficient, multifunctional enzymes.
• Much of the planet's biochemistry may be performed by enzymes differing from highly active textbook examples.