Cloning, expression and medium optimization of validamycin glycosyltransferase from Streptomyces hygroscopicus var. jinggangensis for the biotransformation of validoxylamine A to produce validamycin A using free resting cells

Comparative genomic analysis of azasugar biosynthesis

Azasugars are monosaccharide analogs in which the ring oxygen is replaced with a nitrogen atom. These well-known glycosidase inhibitors are of interest as therapeutics, yet several aspects of azasugars remain unknown including their distribution, structural diversity, and chemical ecology. The hallmark signature of bacterial azasugar biosynthesis is a three gene cluster (3GC) coding for aminotransferase, phosphatase, and dehydrogenase enzymes. Using the bioinformatics platform Enzyme Similarity Tool (EST), we identified hundreds of putative three gene clusters coding for azasugar production in microbial species. In the course of this work, we also report a consensus sequence for the aminotransferase involved in azasugar biosynthesis as being: SGNXFRXXXFPNXXXXXXXLXVPXPYCXRC. Most clusters are found in Bacillus and Streptomyces species which typically inhabit soil and the rhizosphere, but some clusters are found with diverse species representation such as Photorhabdus and Xenorhabdus which are symbiotic with entomopathogenic nematodes; the human skin commensal Cutibacterium acnes, and the marine Bacillus rugosus SPB7, a symbiont to the sea sponge Spongia officinalis. This pan-taxonomic survey of the azasugar 3GC signature may lead to the identification of new azasugar producers, facilitate studies of their natural functions, and lead to new potential therapeutics.

Enzymatic characterization of a NADH-dependent diaphorase from Lysinibacillus sp. strain PAD-91

Diaphorases are flavin-containing enzymes with potential applications in biotransfomation reactions, biosensor design and in vitro diagnostic tests. In this paper, we present recombinant expression, characterization and medium optimization of a lipoamide dehydrogenase (DLD) with NADH-dependent diaphorase activity from a Lysinibacillus sp. strain. DLD encoding sequence showed an open reading frame of 1413-bp encoding a 470 amino acid chain. Lysinibacillus sp. DLD catalyzed the NADH-dependent reduction of electron acceptors and exhibited diaphorase activity. The molecular mass of the isolated enzyme was found to be about 50 kDa, and determined to be a monomeric protein. The optimum pH and temperature for the catalytic activity of the enzyme was about pH 7.5 and 30 °C. The K_m and V_max values were estimated to be 0.025 mM and 1.33 μmol/min, respectively. Recombinant enzyme was optimally produced in fermentation medium containing 10 g/L sucrose, 25 g/L yeast extract, 5 g/L NaCl and 0.25 g/L MgSO₄. By Scaling up fermentation from flask to bioreactor, enzyme activity was increased to 487.5 U/ml. This study provides data on the identification, characterization and medium optimization of a NADH-dependent diaphorase from a newly isolated Lysinibacillus sp. PAD-91.

Medium Optimization for Improved Production of Dihydrolipohyl Dehydrogenase from Bacillus sphaericus PAD-91 in Escherichia coli

Dihydrolipohyl dehydrogenase (DLD) is a FAD-dependent enzyme that catalyzes the reversible oxidation of dihydrolipoamide. Herein, we report medium optimization for the production of a recombinant DLD with NADH-dependent diaphorase activity from a strain of Bacillus sphaericus PAD-91. The DLD gene that consisted of 1413 bp was expressed in Escherichia coli BL21 (DE3), and its enzymatic properties were studied. The composition of production medium was optimized using one-variable-at-a-time method followed by response surface methodology (RSM). B. sphaericus DLD catalyzed the reduction of lipoamide by NAD⁺ and exhibited diaphorase activity. The molecular weight of enzyme was about 50 kDa and determined to be a monomeric protein. Recombinant diaphorase showed its optimal activity at temperature of 30 °C and pH 8.5. K _m and V _max values with NADH were estimated to be 0.025 mM and 275.8 U/mL, respectively. Recombinant enzyme was optimally produced in fermentation medium containing 10 g/L sucrose, 25 g/L yeast extract, 5 g/L NaCl and 0.25 g/L MgSO₄. At these concentrations, the actual diaphorase activity was calculated to be 345.0 ± 4.1 U/mL. By scaling up fermentation from flask to bioreactor, enzyme activity was increased to 486.3 ± 5.5 U/mL. Briefly, a DLD with diaphorase activity from a newly isolated B. sphaericus PAD-91 was characterized and the production of recombinant enzyme was optimized using RSM technique.