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A Arisawa

Publications and source records attributed to A Arisawa.

10 recordsLinked to original sources
PubMed2001

Laboratory evolution of toluene dioxygenase to accept 4-picoline as a substrate.

We are using directed evolution to extend the range of dioxygenase-catalyzed biotransformations to include substrates that are either poorly accepted or not accepted at all by the naturally occurring enzymes. Here we report on the oxidation of a heterocyclic substrate, 4-picoline, by toluene dioxygenase (TDO) and improvement of the enzyme's activity by laboratory evolution. The biotransformation of 4-picoline proceeds at only approximately 4.5% of the rate of the natural reaction on toluene. Random mutagenesis, saturation mutagenesis, and screening directly for product formation using a modified Gibbs assay generated mutant TDO 3-B38, in which the wild-type stop codon was replaced with a codon encoding threonine. Escherichia coli-expressed TDO 3-B38 exhibited 5.6 times higher activity toward 4-picoline and approximately 20% more activity towards toluene than wild-type TDO. The product of the biotransformation of 4-picoline is 3-hydroxy-4-picoline; no cis-diols of 4-picoline were observed.

Amino Acid Sequence↗
PubMed2001

A versatile high throughput screen for dioxygenase activity using solid-phase digital imaging.

We have developed a solid-phase, high throughput (10,000 clones/day) screen for dioxygenase activity. The cis-dihydrodiol product of dioxygenase bioconversion is converted to a phenol by acidification or to a catechol by reaction with cis-dihydrodiol dehydrogenase. Gibbs reagent reacts quickly with these oxygenated aromatics to yield colored products that are quantifiable using a microplate reader or by digital imaging and image analysis. The method is reproducible and quantitative at product concentrations of only 30 microM, with essentially no background from media components. This method is an effective general screen for aromatic oxidation and should be a useful tool for the discovery and directed evolution of oxygenases.

Automation↗
PubMed1999

A high-throughput digital imaging screen for the discovery and directed evolution of oxygenases.

BACKGROUND: Oxygenases catalyze the hydroxylation of a wide variety of organic substrates. An ability to alter oxygenase substrate specificities and improve their activities and stabilities using recombinant DNA techniques would expand their use in processes such as chemical synthesis and bioremediation. Discovery and directed evolution of oxygenases require efficient screens that are sensitive to the activities of interest and can be applied to large numbers of crude enzyme samples. RESULTS: Horseradish peroxidase (HRP) couples the phenolic products of hydroxylation of aromatic substrates to generate colored and/or fluorescent compounds that are easily detected spectroscopically in high-throughput screening. Coexpression of the coupling enzyme with a functional mono- or dioxygenase creates a pathway for the conversion of aromatic substrates into fluorescent compounds in vivo. We used this approach for detecting the products of the toluene-dioxygenase-catalyzed hydroxylation of chlorobenzene and to screen large mutant libraries of Pseudomonas putida cytochrome P450cam by fluorescence digital imaging. Colors generated by the HRP coupling reaction are sensitive to the site of oxygenase-catalyzed hydroxylation, allowing the screen to be used to identify catalysts with new or altered regiospecificities. CONCLUSIONS: The coupled oxygenase-peroxidase reaction system is well suited for screening oxygenase libraries to identify mutants with desired features, including higher activity or stability and altered reaction specificity. This approach should also be useful for screening expressed DNA libraries and combinatorial chemical libraries for hydroxylation catalysts and for optimizing oxygenase reaction conditions.

Camphor 5-Monooxygenase↗
PubMed1996

Direct fermentative production of acyltylosins by genetically-engineered strains of Streptomyces fradiae.

A tylosin-producer, Streptomyces fradiae, was transformed with plasmids carrying genes from Streptomyces thermotolerans that are involved in acyl modification of macrolide antibiotics. A transformant with pMAB3, in which macrolide 4"-O-acyltransferase gene (acyB1) and its regulatory gene (acyB2) are subcloned, produced several types of 4"-O-acyltylosins. A transformant with pAB11 delta EH containing macrolide 3-O-acyltransferase gene (acyA) in addition to the above two genes produced 3-O-acetyltylosin and 3-O-acetyl-4"-O-acyltylosins. Among the products of the latter transformant, 3-O-acetyl-4"-O-isovaleryltylosin (AIV) was detected as a minor component. When L-leucine, a precursor of isovaleryl-CoA, was added to the medium at the late stage of the fermentation, AIV content among the total macrolides increased ten-fold and AIV became a main product. This fact suggests that a high level of endogenous isovaleryl-CoA may be essential for the selective production of AIV by S. fradiae carrying pAB11 delta EH.

Acylation↗
PubMed1995

Nucleotide sequence analysis of the carbomycin biosynthetic genes including the 3-O-acyltransferase gene from Streptomyces thermotolerans.

A 3.2-kb DNA fragment of the carbomycin biosynthetic region including the 3-O-acyltransferase gene (acyA) from Streptomyces thermotolerans was sequenced, and four ORFs were found in the fragment. The second ORF, designated ORF-A, was transcribed in the opposite direction to the other three ORFs. The first ORF was identified as carA, a gene for carbomycin resistance. The amino acid sequence of ORF-A was homologous to proteins of the cytochrome P-450 family. Streptomyces lividans transformed with pCB20, in which ORF-A was subcloned, epoxidized carbomycin B at its C-12, 13 positions, thus producing carbomycin A. The third ORF, the amino acid sequence of which showed a homology to macrolide antibiotics O-acyltransferases was identified as acyA. The last ORF (ORF-B), which starts just 3 bp downstream from the TGA termination codon of acyA, was thought to be a carbomycin 4-O-methyltransferase gene, because the amino acid sequence deduced from ORF-B showed high homology to a putative midecamycin 4-O-methyltransferase encoded on mdmC.

Acetyltransferases↗
PubMed1994

Cloning of the macrolide antibiotic biosynthesis gene acyA, which encodes 3-O-acyltransferase, from Streptomyces thermotolerans and its use for direct fermentative production of a hybrid macrolide antibiotic.

A gene encoding the macrolide modification enzyme 3-O-acyltransferase (acyA) was cloned by chromosome walking onto the carbomycin biosynthetic region in Streptomyces thermotolerans TH475, with the 3' region of the gene encoding the macrolide modification enzyme 4"-O-acyltransferase (acyB1) as a probe. A shortened fragment (1.8 kb) containing acyA was subcloned with pIJ350. A high-level tylosin producer, Streptomyces fradiae MBBF, transformed with the plasmid could produce a hybrid macrolide, 3-O-acetyltylosin, most efficiently.

Acyltransferases↗
PubMed1993

Cloning and nucleotide sequences of two genes involved in the 4''-O-acylation of macrolide antibiotics from Streptomyces thermotolerans.

A DNA fragment responsible for the 4''-O-acylation of macrolide antibiotics was cloned from a mutant strain of the carbomycin producer Streptomyces thermotolerans. The gene encoding the macrolide 4''-O-acyltransferase was within a 2.7-kb region of the cloned fragment (15-kb). Streptomyces lividans carrying the region converted exogenously added tylosin to 4''-O-acyltylosins. Nucleotide sequencing of the region showed two open reading frames (ORFs). Expression assay using deleted plasmids showed that both ORFs were essential for optimal expression of the acyltransferase activity. One of them (acyB1) was identical with carE reported previously as a gene encoding 4''-mycarosyl isovaleryl-CoA transferase. The other (acyB2) was assumed to encode a novel regulatory protein that could active acyB1 expression. acyB1 and acyB2 were highly conserved among streptomycetes with macrolide 4''-O-acyl transferase activity.

Acylation↗
PubMed1987

Characterization of rat c-myc and adjacent regions.

Rat genomic regions covering c-myc were cloned from the DNA of both normal liver and two lines of Morris hepatomas, one of which had c-myc amplification. The three restriction maps showed perfect agreement within the overlapping regions. The 7 kb regions, which included the entire normal rat c-myc and the region 2.2 kb upstream, and one from the hepatomas, were sequenced and found to be identical. The coding regions of exons 2 and 3 were highly conserved between rat, mouse and man, but some differences in amino acids were noted. Exon 1 and the non-coding region of exon 3 showed limited homology between the three species. Rat exon 1 contained several nonsense codons in each frame and no ATG codon, indicating there to be no coding capacity in this exon. The 2.2 kb upstream regions and the introns compared showed unusual conservation between the rat and human genes. Some motifs, previously proposed as having a functional role in human c-myc, were also found in equivalent positions of the rat sequence. Nucleas S1 protection mapping revealed the second promoter to be preferentially used in most tissues or in hepatoma cells, and the second poly A addition signal to be the only one functional in all the RNA sources examined.

Amino Acid Sequence↗