In vivo and in vitro FMN prenylation and (de)carboxylase activation under aerobic conditions

Prenylated FMN (prFMN) is a newly discovered redox cofactor required for activity of the large family of reversible UbiD (de)carboxylases involved in biotransformation of aromatic, heteroaromatic, and unsaturated aliphatic acids (White et al., 2015). Despite the growing demand for decarboxylases in the pulp/paper industry and in forest biorefineries, the vast majority of UbiD-like decarboxylases remain uncharacterized. Functional characterization of the novel UbiD decarboxylases is hindered by the lack of prFMN generating system. prFMN cofactor is synthesized by the UbiX family of FMN prenyltransferases, which use reduced FMN as substrate under anaerobic conditions and dimethylallyl-monophosphate (DMAP) as the prenyl group donor. Here, we report the in vivo and in vitro biosynthesis of prFMN and UbiD activation under aerobic conditions. For in vivo biosynthesis, we used newly discovered UbiX proteins from Salmonella typhimurium and Klebsiella pneumonia, which activated ferulic acid UbiD decarboxylase Fdc1 from Aspergillus niger under aerobic conditions (0.5-1.5 U/mg). For in vitro biosynthesis of prFMN and UbiD activation, we established a one-pot enzyme cascade system that uses prenol, polyphosphate, formate, and riboflavin as starting substrates and (re)generates DMAP, ATP, FMN and NADH. The system contains 6 different enzymes: prenol kinase, polyphosphate kinase, formate dehydrogenase, FMN reductase, riboflavin kinase and FMN prenyltransferase. Under aerobic conditions, this system showed up to 80% conversion of FMN to prFMN and generated active Fdc1 decarboxylase (0.2-1 U/mg). Thus, both systems represent robust approaches for in vivo and in vitro prFMN biosynthesis and UbiD activation under aerobic conditions. The developed FMN prenylation systems will facilitate the exploration and biochemical characterization of UbiD-like decarboxylases and their applications in biocatalysis. Please click Additional Files below to see the full abstract

Experimental validation of in silico model-predicted isocitrate dehydrogenase and phosphomannose isomerase from Dehalococcoides mccartyi

Gene sequences annotated as proteins of unknown or non-specific function and hypothetical proteins account for a large fraction of most genomes. In the strictly anaerobic and organohalide respiring Dehalococcoides mccartyi, this lack of annotation plagues almost half the genome. Using a combination of bioinformatics analyses and genome-wide metabolic modelling, new or more specific annotations were proposed for about 80 of these poorly annotated genes in previous investigations of D. mccartyi metabolism. Herein, we report the experimental validation of the proposed reannotations for two such genes (KB1_0495 and KB1_0553) from D. mccartyi strains in the KB-1 community. KB1_0495 or DmIDH was originally annotated as an NAD[superscript +]-dependent isocitrate dehydrogenase, but biochemical assays revealed its activity primarily with NADP[superscript +] as a cofactor. KB1_0553, also denoted as DmPMI, was originally annotated as a hypothetical protein/sugar isomerase domain protein. We previously proposed that it was a bifunctional phosphoglucose isomerase/phosphomannose isomerase, but only phosphomannose isomerase activity was identified and confirmed experimentally. Further bioinformatics analyses of these two protein sequences suggest their affiliation to potentially novel enzyme families within their respective larger enzyme super families.University of TorontoNatural Sciences and Engineering Research Council of CanadaGenome Canada (Firm) (Ontario Genomics Institute 2009-OGI-ABC-1405)United States. Dept. of Defense. Strategic Environmental Research and Development Progra

Structure of SAICAR synthase from Thermotoga maritima at 2.2 Å reveals an unusual covalent dimer

The crystal structure of phophoribosylaminoimidazole-succinocarboxamide or SAICAR synthase from T. maritima at 2.2 Å revealed an unusual covalent dimer

PoxA, YjeK and Elongation Factor P Coordinately Modulate Virulence and Drug Resistance in \u3cem\u3eSalmonella enterica\u3c/em\u3e

We report an interaction between poxA, encoding a paralog of lysyl tRNA-synthetase, and the closely linked yjeK gene, encoding a putative 2,3-β-lysine aminomutase, that is critical for virulence and stress resistance in Salmonella enterica. Salmonella poxA and yjeK mutants share extensive phenotypic pleiotropy, including attenuated virulence in mice, an increased ability to respire under nutrient-limiting conditions, hypersusceptibility to a variety of diverse growth inhibitors, and altered expression of multiple proteins, including several encoded on the SPI-1 pathogenicity island. PoxA mediates posttranslational modification of bacterial elongation factor P (EF-P), analogous to the modification of the eukaryotic EF-P homolog, eIF5A, with hypusine. The modification of EF-P is a mechanism of regulation whereby PoxA acts as an aminoacyl-tRNA synthetase that attaches an amino acid to a protein resembling tRNA rather than to a tRNA

Structural and biochemical studies of novel Aldo-keto Reductases (AKRs) for the biocatalytic conversion of 3-hydroxybutanal to 1,3-butanediol

The non-natural alcohol 1,3-butanediol (1,3-BDO) is a valuable building block for the synthesis of various polymers. One of the potential pathways for the biosynthesis of 1,3-BDO includes the biotransformation of acetaldehyde to 1,3-BDO via 3-hydroxybutanal (3-HB) using aldolases and aldo-keto reductases. This pathway requires an aldo-keto reductase (AKR) selective for 3-HB, but inactive toward acetaldehyde, so it can be used for one pot synthesis. In this work, we screened over 20 purified uncharacterized AKRs for 3-HB reduction and identified 10 enzymes with significant activity and nine proteins with detectable activity. PA1127 from Pseudomonas aeruginosa showed the highest activity and was selected for comparative studies with STM2406 from Salmonella typhimurium, for which we have determined the crystal structure. Both AKRs used NADPH as cofactor, reduced a broad range of aldehydes, and showed low activity toward acetaldehyde. The crystal structures of STM2406 in complex with cacodylate or NADPH revealed the active site with bound molecules of a substrate mimic or cofactor. Site-directed mutagenesis of STM2406 and PA1127 identified the key residues important for activity against 3-HB and aromatic aldehydes, which include the residues of the substrate binding pocket and C-terminal loop. Our results revealed that the replacement of the STM2406 Asn65 by Met enhanced both activity and affinity of this protein toward 3-HB resulting in a seven-fold increase in kcat/Km. Our work provided further insights into the molecular mechanisms of substrate selectivity of AKRs and rational design of these enzymes towards new substrates. Importance In this study, we identified several aldo-keto reductases with significant activity in the reduction of 3-hydroxybutanal to 1,3-BDO, an important commodity chemical. Biochemical and structural studies of these enzymes revealed the key catalytic and substrate binding residues including the two structural determinants necessary for high activity in the biosynthesis of 1,3-BDO. This work expands our understanding of the molecular mechanisms of substrate selectivity of AKRs and the potential for protein engineering of these enzymes for applications in the biocatalytic production of 1,3-BDO and other valuable chemicals