Expression and purification of the 5'-nucleotidase YitU from Bacillus species: its enzymatic properties and possible applications in biotechnology.

5'-Nucleotidases (EC 3.1.3.5) are enzymes that catalyze the hydrolytic dephosphorylation of 5'-ribonucleotides and 5'-deoxyribonucleotides to their corresponding nucleosides plus phosphate. In the present study, to search for new genes encoding 5'-nucleotidases specific for purine nucleotides in industrially important Bacillus species, "shotgun" cloning and the direct selection of recombinant clones grown in purine nucleosides at inhibitory concentrations were performed in the Escherichia coli GS72 strain, which is sensitive to these compounds. As a result, orthologous yitU genes from Bacillus subtilis and Bacillus amyloliquefaciens, whose products belong to the ubiquitous haloacid dehalogenase superfamily (HADSF), were selected and found to have a high sequence similarity of 87%. B. subtilis YitU was produced in E. coli as an N-terminal hexahistidine-tagged protein, purified and biochemically characterized as a soluble 5'-nucleotidase with broad substrate specificity with respect to various deoxyribo- and ribonucleoside monophosphates: dAMP, GMP, dGMP, CMP, AMP, XMP, IMP and 5-aminoimidazole-4-carboxamide-1-ß-D-ribofuranosyl 5'-monophosphate (AICAR-P). However, the preferred substrate for recombinant YitU was shown to be flavin mononucleotide (FMN). B. subtilis and B. amyloliquefaciens yitU overexpression increased riboflavin (RF) and 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR) accumulation and can be applied to breed highly performing RF- and AICAR-producing strains.

Identification, Heterologous Expression, and Functional Characterization of Bacillus subtilis YutF, a HAD Superfamily 5'-Nucleotidase with Broad Substrate Specificity.

5'-nucleotidases (EC 3.1.3.5) catalyze the hydrolytic dephosphorylation of 5'-ribonucleotides and 5'-deoxyribonucleotides as well as complex nucleotides, such as uridine 5'-diphosphoglucose (UDP-glucose), nicotinamide adenine dinucleotide and flavin adenine dinucleotide, to their corresponding nucleosides plus phosphate. These enzymes have been found in diverse species in intracellular and membrane-bound, surface-localized forms. Soluble forms of 5'-nucleotidases belong to the ubiquitous haloacid dehalogenase superfamily (HADSF) and have been shown to be involved in the regulation of nucleotide, nucleoside and nicotinamide adenine dinucleotide (NAD+) pools. Despite the important role of 5'-nucleotidases in cellular metabolism, only a few of these enzymes have been characterized in the Gram-positive bacterium Bacillus subtilis, the workhorse industrial microorganism included in the Food and Drug Administration's GRAS (generally regarded as safe) list. In the present study, we report the identification of a novel 5'-nucleotidase gene from B. subtilis, yutF, which comprises 771 bp encoding a 256-amino-acid protein belonging to the IIA subfamily of the HADSF. The gene product is responsible for the major p-nitrophenyl phosphatase activity in B. subtilis. The yutF gene was overexpressed in Escherichia coli, and its product fused to a polyhistidine tag was purified and biochemically characterized as a soluble 5'-nucleotidase with broad substrate specificity. The recombinant YutF protein was found to hydrolyze various purine and pyrimidine 5'-nucleotides, showing preference for 5'-nucleoside monophosphates and, specifically, 5'-XMP. Recombinant YutF also exhibited phosphohydrolase activity toward nucleotide precursors, ribose-5-phosphate and 5-phosphoribosyl-1-pyrophosphate. Determination of the kinetic parameters of the enzyme revealed a low substrate specificity (Km values in the mM concentration range) and modest catalytic efficiencies with respect to substrates. An initial study of the regulation of yutF expression showed that the yutF gene is a component of the yutDEF transcription unit and that YutF overproduction positively influences yutDEF expression.

Wild-type and feedback-resistant phosphoribosyl pyrophosphate synthetases from Bacillus amyloliquefaciens: purification, characterization, and application to increase purine nucleoside production.

Bacillus strains are used for the industrial production of the purine nucleosides inosine and guanosine, which are raw materials for the synthesis of the flavor enhancers disodium inosinate and disodium guanylate. An important precursor of purine nucleosides is 5-phospho-α-D: -ribosyl-1-pyrophosphate, which is synthesized by phosphoribosyl pyrophosphate synthetase (PRS, EC 2.7.6.1). Class I PRSs are widespread in bacteria and mammals, are highly conserved among different organisms, and are negatively regulated by two end products of purine biosynthesis, adenosine 5'-diphosphate (ADP) and guanosine 5'-diphosphate (GDP). The D52H, N114S, and L129I mutations in the human PRS isozyme I (PRS1) have been reported to cause uric acid overproduction and gout due to allosteric deregulation and enzyme superactivity. In this study, to find feedback-resistant Bacillus amyloliquefaciens PRS, the influence of the D58H, N120S, and L135I mutations (corresponding to the D52H, N114S, and L129I mutations in PRS1, respectively) on PRS enzymatic properties has been studied. Recombinant histidine-tagged wild-type PRS and three mutant PRSs were expressed in Escherichia coli, purified, and characterized. The N120S and L135I mutations were found to release the enzyme from ADP and GDP inhibition and significantly increase its sensitivity to inorganic phosphate (P(i)) activation. In contrast, PRS with the D58H mutation exhibited nearly identical sensitivity to ADP and GDP as the wild-type protein and had a notably greater P(i) requirement for activation. The N120S and L135I mutations improved B. amyloliquefaciens and Bacillus subtilis purine nucleoside-producing strains.