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Applied and Environmental Microbiology, July 2006, p. 4878-4884, Vol. 72, No. 7
0099-2240/06/$08.00+0     doi:10.1128/AEM.00712-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

YtjE from Lactococcus lactis IL1403 Is a C-S Lyase with ,-Elimination Activity toward Methionine

M. Carmen Martínez-Cuesta,^1* Carmen Peláez,¹ John Eagles,² Michael J. Gasson,² Teresa Requena,¹ and Sean B. Hanniffy²

Department of Dairy Science and Technology, Instituto del Frío (CSIC), José Antonio Novais 10, Madrid 28040, Spain,¹ Food Safety Science Division, Institute of Food Research, Norwich Research Park, Colney Lane, Norwich, Norfolk NR4 7UA, United Kingdom²

Received 28 March 2006/ Accepted 16 May 2006

Cheese microbiota and the enzymatic conversion of methionine to volatile sulfur compounds (VSCs) are important factors in flavor formation during cheese ripening and the foci in biotechnological approaches to flavor improvement. The product of ytjE of Lactococcus lactis IL1403, suggested to be a methionine-specific aminotransferase based on genome sequence analysis, was therefore investigated for its role in methionine catabolism. The ytjE gene from Lactococcus lactis IL1403 was cloned in Escherichia coli and overexpressed and purified as a recombinant protein. When tested, the YtjE protein did not exhibit a specific methionine aminotransferase activity. Instead, YtjE exhibited C-S lyase activity and shared homology with the MalY/PatC family of enzymes involved in the degradation of L-cysteine, L-cystine, and L-cystathionine. YtjE was also shown to exhibit ,-elimination activity toward L-methionine. In addition, gas chromatographic-mass spectrometry analysis showed that YtjE activity resulted in the formation of H₂S from L-cysteine and methanethiol (and its oxidized derivatives dimethyl disulfide and dimethyl trisulfide) from L-methionine. Given their significance in cheese flavor development, VSC production by YtjE could offer an additional approach for the development of cultures with optimized aromatic properties.

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* Corresponding author. Mailing address: Department of Dairy Science and Technology, Instituto del Frío, C/José Antonio Novais 10, Ciudad Universitaria, Madrid 28040, Spain. Phone: 34915492300. Fax: 34915493627. E-mail: ifrcm94{at}if.csic.es.

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Applied and Environmental Microbiology, July 2006, p. 4878-4884, Vol. 72, No. 7
0099-2240/06/$08.00+0     doi:10.1128/AEM.00712-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

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