Isolation, sequence, and bacterial expression of a cDNA for (S)-tetrahydroberberine oxidase from cultured berberine-producing Coptis japonica cells.

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Abstract
CDNA clones for the (S)-tetrahydroberberine (H4Ber) oxidase of cultured berberine-producing Coptis japonica cells were isolated by screening a C. japonica cDNA library with synthetic nucleotides that can encode the NH2-terminal sequence of this enzyme. Analyses of the nucleotide sequences of the cloned cDNA inserts revealed a 759-base-pair open reading frame that encoded a 253-amino acid polypeptide with a Mr of 27,089 and NH2-terminal and internal sequences identical with those of the (S)-H4Ber oxidase, as determined by microsequencing methods. Escherichia coli were transformed with an expression vector carrying (S)-H4Ber oxidase cDNA. The transformed bacteria were induced to overproduce a 28-kDa protein that reacted with Coptis (S)-H4Ber oxidase-specific antibody. A comparison of the derived amino acid sequence of (S)-H4Ber oxidase with sequences in the protein data base of the Protein Research Foundation showed a marked similarity between (S)-H4Ber oxidase and the NH2-terminal portion of mouse P1-450, which is encoded by a single exon of the mouse P1-450 gene. The availability of cloned cDNA for (S)-H4Ber oxidase allows use of the methods of molecular biology to study the regulation of (S)-H4Ber oxidase gene expression in cultured C. japonica cells in relation to berberine biosynthesis.