Immunochemical studies on Rhodotorula gracilis D-amino acid oxidase

Construction of a D-amino acid oxidase reactor based on magnetic nanoparticles modified by a reactive polymer and its application in screening enzyme inhibitors

Developing facile and high-throughput methods for exploring pharmacological inhibitors of D-amino acid oxidase (DAAO) has triggered increasing interest. In this work, DAAO was immobilized on the magnetic nanoparticles, which were modified by a biocompatible reactive polymer, poly(glycidyl methacrylate) (PGMA) via an atom transfer radical polymerization technique. Interestingly, the enzyme immobilization process was greatly promoted with the assistance of a lithium perchlorate catalyst. Meanwhile, a new amino acid ionic liquid (AAIL) was successfully synthesized and employed as the efficient chiral ligand in a chiral ligand exchange capillary electrophoresis (CLE-CE) system for chiral separation of amino acids (AAs) and quantitation of methionine, which was selected as the substrate of DAAO. Then, the apparent Michaelis-Menten constants in the enzyme system were determined with the proposed CLE-CE method. The prepared DAAO-PGMA-Fe3O4 nanoparticles exhibited excellent reusability and good stability. Moreover, the enzyme reactor was successfully applied in screening DAAO inhibitors. These results demonstrated that the enzyme could be efficiently immobilized on the polymer-grafted magnetic nanoparticles and that the obtained enzyme reactor has great potential in screening enzyme inhibitors, further offering new insight into monitoring the relevant diseases.

Evolution of an acylase active on cephalosporin C

Semisynthetic cephalosporins are synthesized from 7-amino cephalosporanic acid, which is produced by chemical deacylation or by a two-step enzymatic process of the natural antibiotic cephalosporin C. The known acylases take glutaryl-7-amino cephalosporanic acid as a primary substrate, and their specificity and activity are too low for cephalosporin C. Starting from a known glutaryl-7-amino cephalosporanic acid acylase as the protein scaffold, an acylase gene optimized for expression in Escherichia coli and for molecular biology manipulations was designed. Subsequently we used error-prone PCR mutagenesis, a molecular modeling approach combined with site-saturation mutagenesis, and site-directed mutagenesis to produce enzymes with a cephalosporin C/glutaryl-7-amino cephalosporanic acid catalytic efficiency that was increased up to 100-fold, and with a significant and higher maximal activity on cephalosporin C as compared to glutaryl-7-amino cephalosporanic acid (e.g., 3.8 vs. 2.7 U/mg protein, respectively, for the A215Y-H296S-H309S mutant). Our data in a bioreactor indicate an ~90% conversion of cephalosporin C to 7-amino-cephalosporanic acid in a single deacylation step. The evolved acylase variants we produced are enzymes with a new substrate specificity, not found in nature, and represent a hallmark for industrial production of 7-amino cephalosporanic acid.

Regulation of D-amino acid oxidase expression in the yeast Rhodotorula gracilis

Rhodotorula gracilis is a oleaginous yeast which utilizes D-amino acids as a source of carbon and/or nitrogen. D-amino acid oxidase (DAAO), which converts D-amino acids in the corresponding alpha-keto acids and ammonia, is the first enzyme involved in the catabolism of D-amino acids. DAAO activity is induced by the presence of D-alanine, but the presence of the L-isomer prevents induction by inhibiting the transport of D-alanine into cells. To understand how DAAO expression is regulated, R. gracilis cells were grown on media containing different nitrogen and/or carbon sources. As a general rule, the level of DAAO mRNA reached a maximum after 15 h growth and preceded by approximately 6 h the maximum level of DAAO activity. The inducer D-alanine acts by increasing the rate of DAAO mRNA transcription: the increase in DAAO expression is due essentially to de novo synthesis. The presence of a supplemental carbon source (e.g. succinate or glucose) does not repress DAAO expression. Ammonium sulphate appears to have a negative effect on DAAO mRNA translation and on the expression of DAAO activity: DAAO is only partially active when the yeast is grown in the presence of D-alanine and ammonium sulphate. The best expression of DAAO activity was obtained by growing the cells for 12 h at 30 degrees C in the presence of glucose and D-alanine using cells pre-cultured for 10 h on glucose and L-alanine (0.99 U/mg protein, corresponding to approximately 1.0% total proteins in the crude extract). Under these growth conditions a six-fold increase in DAAO production was achieved.

Overexpression of a recombinant wild-type and His-tagged Bacillus subtilis glycine oxidase in Escherichia coli

We have cloned the gene coding for the Bacillus subtilis glycine oxidase (GO), a new flavoprotein that oxidizes glycine and sarcosine to the corresponding alpha-keto acid, ammonia and hydrogen peroxide. By inserting the DNA encoding for GO into the multiple cloning site of the expression vector pT7.7 we produced a recombinant plasmid (pT7-GO). The pT7-GO encodes a fully active fusion protein with six additional residues at the N-terminus of GO (MARIRA). In BL21(DE3)pLysS Escherichia coli cells, and under optimal isopropyl thio-beta-D-galactoside induction conditions, soluble and active chimeric GO was expressed up to 1.14 U g(-1) of cell (and a fermentation yield of 3.82 U x L(-1) of fermentation broth). An N-terminal His-tagged protein (HisGO) was also successfully expressed in E. coli as a soluble protein and a fully active holoenzyme. HisGO represents approximately 3.9% of the total soluble protein content of the cell. The His-tagged GO was purified in a single step by nickel-chelate chromatography to a specific activity of 1.06 U x mg(-1) protein at 25 degrees C and with a yield of 98%. The characterization of the purified enzyme showed that GO is a homotetramer of approximately 180 kDa with the spectral properties typical of flavoproteins. GO exhibits good thermal stability, with a Tm of 46 degrees C after 30 min incubation; its stability is maximal in the 7.0-8.5 pH range. A comparison of amino-acid sequence and substrate specificity indicates that GO has similarities to other flavoenzymes acting on primary amines and on D-amino acids.

Xenopus allantoicase: molecular cloning, enzymatic activity and developmental expression

Allantoicase is one of the enzymes of the purine degradation pathway and, interestingly, it appears to be lost, together with uricase and allantoinase, during mammalian evolution. Only allantoicases from the ascomycetes S. pombe, S. cerevisiae, and N. crassa have already been cloned, although the activity has been reported also in fishes and amphibians. By screening a cDNA expression library of Xenopus liver, we have cloned a 1491-bp-length cDNA coding for a 389 amino acid protein that shows an high similarity with the enzyme allantoicase. We have found that allantoicase mRNA is abundantly expressed in kidney and liver, but at much lower level is also present in brain, testis, intestine, and lung. We have detected enzymatic activity in crude extract from kidney, liver, and lung; we have also determined kinetic parameters (K(m) = 8.44 mM, V(max) = 6. 94 micromol min(-1) per mg protein) in kidney. During embryo development, we have detected allantoicase transcript and activity starting from 1 and 5 days after fertilization, respectively.

Cloning, sequencing and expression in E. coli of a D-amino acid oxidase cDNA from Rhodotorula gracilis active on cephalosporin C

We have cloned the cDNA coding for the Rhodotorula gracilis D-amino acid oxidase (DAAO), an enzyme that performs with high catalytic efficiency biotechnologically relevant bioconversions, by PCR amplification. The first strand cDNA was synthesised from the total mRNA fraction isolated from R. gracilis cells grown under DAAO-inducing conditions. The R. gracilis DAAO cDNA consists of 1104 bp encoding a protein of 368 amino acids. The insertion of the cDNA into the pKK223-3 plasmid allowed the expression of recombinant DAAO in Escherichia coli as a wholly soluble and catalytically active holoenzyme (approximately 0.5 U mg-1 protein) with a fermentation yield, in terms of DAAO units, of 800 U l-1. This level of expression allowed the purification, in homogeneous form and high yield (50%), of the recombinant enzyme which showed a high catalytic activity on cephalosporin C as substrate. The nucleotide sequence reported in this paper will appear in the nucleotide sequence databases under accession number.