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J. Biol. Chem., Vol. 281, Issue 2, 824-833, January 13, 2006

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A Novel o-Aminophenol Oxidase Responsible for Formation of the Phenoxazinone Chromophore of Grixazone^*

From the Department of Biotechnology, Graduate School of Agriculture and Life Sciences, University of Tokyo, Bunkyo-ku, Tokyo 113-8657, Japan

Grixazone contains a phenoxazinone chromophore and is a secondary metabolite produced by Streptomyces griseus. In the grixazone biosynthesis gene cluster, griF (encoding a tyrosinase homolog) and griE (encoding a protein similar to copper chaperons for tyrosinases) are encoded. An expression study of GriE and GriF in Escherichia coli showed that GriE activated GriF by transferring copper ions to GriF, as has been observed for a Streptomyces melanogenesis system in which the MelC1 copper chaperon transfers copper ions to MelC2 tyrosinase. In contrast with tyrosinases, GriF showed no monophenolase activity, although it oxidized various o-aminophenols as preferable substrates rather than catechol-type substrates. Deletion of the griEF locus on the chromosome resulted in accumulation of 3-amino-4-hydroxybenzaldehyde (3,4-AHBAL) and its acetylated compound, 3-acetylamino-4-hydroxybenzaldehyde. GriF oxidized 3,4-AHBAL to yield an o-quinone imine derivative, which was then non-enzymatically coupled with another molecule of the o-quinone imine to form a phenoxazinone. The coexistence of N-acetylcysteine in the in vitro oxidation of 3,4-AH-BAL by GriF resulted in the formation of grixazone A, suggesting that the –SH group of N-acetylcysteine is conjugated to the o-quinone imine formed from 3,4-AHBAL and that the conjugate is presumably coupled with another molecule of the o-quinone imine. GriF is thus a novel o-aminophenol oxidase that is responsible for the formation of the phenoxazinone chromophore in the grixazone biosynthetic pathway.

Received for publication, May 27, 2005 , and in revised form, October 19, 2005.

^* This work was supported by Grant 03A07002 from the Industrial Technology Research Grant Program in 2003 of the New Energy and Industrial Technology Development Organization of Japan, by a grant-in-aid for scientific research on priority areas from Monkasho, and by the BioDesign Program of the Ministry of Agriculture, Forestry, and Fisheries of Japan. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

The nucleotide sequence(s) reported in this paper has been submitted to the GenBank^TM/EBI Data Bank with accession number(s) AB214954 [GenBank] .

¹ To whom correspondence should be addressed. Tel.: 81-3-5841-5123; Fax: 81-3-5841-8021; E-mail: asuhori{at}mail.ecc.u-tokyo.ac.jp.

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