Crystal structure of MJ0684 from Methanococcus jannaschii, a novel archaeal homolog of kynurenine aminotransferase

MJ0684 from Methanococcus jannaschii is a hypothetical protein belonging to the subfamily I gamma of amino acid aminotransferases. In the present study, the crystal structure of MJ0684 has been determined at 2.2 angstrom resolution. It reveals that MJ0684 has an overall structure similar to subfamily I gamma aminotransferases and its active site architecture is most similar to that of kynurenine aminotransferases among several kinds of aminotransferases in the subfamily I gamma. It has two hydrophobic active site residues conserved in the kynurenine aminotransferases for recognizing hydrophobic substrates. In addition, the absence of any basic residue for recognizing the side chain carboxylic group of the aspartate in the active site rules out the possibility that MJ0684 would act as an aspartate aminotransferase. These structural observations collectively imply that MJ0684 is a novel archaeal homolog of the subfamily I gamma kynurenine aminotransferase.