06/12/2015
Phenolic Amides are Potent Inhibitors of de novo Nucleotide Biosynthesis
Summary
Lignocellulose-derived hydrolysates contain several different inhibitors (collectively called lignotoxins or LTs) that arise during pretreatment of biomass. Determining the mechanisms by which yeast or bacteria are adversely affected by LTs is a key step toward improving the efficiency of fermentation and bioconversion. Prior work has established that LTs present in ammonia pretreated corn stover hydrolysates inhibit growth and sugar utilization in Escherichia coli. Researchers at the Department of Energy’s Great Lakes Bioenergy Research Center (GLBRC) have now keyed in on two phenolic amine LTs, feruloyl amide (FA) and coumaroyl amide (CA). These inhibitors are important because these two alone are sufficient to recapitulate the inhibitory effects of all LTs present. Analysis of the metabolome in untreated versus treated cells indicated that these phenolic amides cause rapid accumulation of 5-phosphoribosyl-1-pyrophosphate (PRPP), a key precursor in nucleotide biosynthesis. Moreover, isotopic tracer studies confirmed that carbon and nitrogen flux into nucleotides is inhibited by the amides, suggesting that these phenolic amines are potent and fast-acting inhibitors of purine and pyrimidine biosynthetic pathways. Biochemical studies showed that the amides directly inhibit glutamine amidotransferases, with FA acting as a competitive inhibitor of the E. coli enzyme responsible for the first committed step in de novo purine biosynthesis. Supplementation of cultures with nucleosides was sufficient to reverse the effect of the amides, suggesting the ability to bypass the block in de novo nucleotide biosynthesis via salvage pathways. Collectively, these results provide a direct mechanism for the inhibitory effects of phenolic amides, knowledge that will inform future design of biocatalysts for improved bioconversion.
References
Pisithkul, T., T. B. Jacobson, T. J. O’Brien, D. M. Stevenson, and D. Amador-Noguez. 2015. “Phenolic Amides are Potent Inhibitors of De Novo Nucleotide Biosynthesis,” Applied and Environmental Microbiology 81(17), 5761-72. DOI: 10.1128/AEM.01324-15.