The Corynebacterium glutamicum aecD gene encodes a C-S lyase with alpha, beta-elimination activity that degrades aminoethylcysteine

S-(beta-Aminoethyl)-cysteine (AEC) resistance was achieved in Corynebacterium glutamicum by cloning a chromosomal 1.5-kb EcoRV-BglII DNA fragment on a multicopy plasmid. DNA sequence analysis of the 1.5-kb DNA fragment revealed an open reading frame (ORF326) which represents the AEC resistance gene, designated aecD. The aecD gene directs the synthesis of a 36-kDa protein which was visualized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The aecD gene is a nonessential gene and mediates AEC resistance only in an amplified state. C. glutamicum strains harboring an amplified aecD gene can utilize AEC as an alternative nitrogen source, indicating that the AEC resistance mechanism is due to AEC degradation. Since the AEC degradation products analyzed by high-pressure liquid chromatography were found to be pyruvate and aminoethanethiol (cysteamine), it was concluded that the aecD gene encodes a C-S lyase with alpha, beta-elimination activity. Besides AEC, the C-S lyase was also able to use cysteine, cystine, and cystathionine as substrates.