Cloning and characterization of two genes encoding a C-S lyase from Lactobacillus casei

Agroscope Liebefeld-Posieux Research Station ALP, Switzerland; Geisenheim Research Center, Germany

	Abstract

Volatile sulfur compounds are key flavor compounds in several cheese types. To better understand the metabolism of sulfur-containing amino acids, which certainly plays a key role in the release of volatile sulfur compounds, we searched the genome database of Lactobacillus casei ATCC 334 for genes encoding putative homologs of enzymes known to degrade cysteine, cystathionine and methionine. The search revealed that L. casei possesses two genes putatively encoding a cystathionine -lyase (EC 4.4.1.8, CBL). The enzyme has been implicated not only in the degradation of cystathionine but also cysteine and methionine. Recombinant CBL proteins catalyzed degradation of L-cystathionine, O-succinyl-L-homoserine, L-cysteine, L-serine, and L-methionine to form alpha-keto acid, hydrogen sulfide or methanethiol. The two enzymes showed notable differences in substrate specificity and pH optimum.