Novel Inhibitors of Glutamyl-tRNAGlu Reductase Identified through Cell-Based Screening of the Heme/Chlorophyll Biosynthetic Pathway

• Published in: Archives of biochemistry and biophysics Vol. 372; no. 2; pp. 230 - 237
• Main Authors: Loida, Paul J., Thompson, Rebecca L., Walker, Dan M., CaJacob, Claire A.
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 15.12.1999
• Subjects: 5-aminolevulinic acid; chlorophyll; glutamyl-tRNA reductase; high-throughput screen; chlorophyll; high-throughput screen; glutamyl-tRNA reductase; 5-aminolevulinic acid
• ISSN: 0003-9861; 1096-0384
• DOI: 10.1006/abbi.1999.1505

The metabolite 5-aminolevulinic acid (ALA) is an early committed intermediate in the biosynthetic pathway of heme and chlorophyll formation. In plants, 5-aminolevulinic acid is synthesized via a two-step pathway in which glutamyl-tRNAGlu is reduced by glutamyl-tRNAGlu reductase (GluTR) to glutamate 1-semialdehyde, followed by transformation to 5-aminolevulinic acid catalyzed by glutamate 1-semialdehyde aminotransferase. Using an Escherichia coli cell-based high-throughput assay to screen small molecule libraries, we identified several chemical classes that specifically inhibit heme/chlorophyll biosynthesis at this point by demonstrating that the observed cell growth inhibition is reversed by supplementing the medium with 5-aminolevulinic acid. These compounds were further tested in vitro for inhibition of the purified enzymes GluTR and glutamate 1-semialdehyde aminotransferase as confirmation of the specificity and site of action. Several promising compounds were identified from the high-throughput screen that inhibit GluTR with an I0.5 of less than 10 μM. Our results demonstrate the efficacy of cell-based high-throughput screening for identifying inhibitors of 5-aminolevulinic acid biosynthesis, thus representing the first report of exogenous inhibitors of this enzyme.