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Applied and Environmental Microbiology, September 2007, p. 5825-5831, Vol. 73, No. 18
0099-2240/07/$08.00+0     doi:10.1128/AEM.00705-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Lactococcus lactis Gene yjgB Encodes a -D-Glutaminyl-L-Lysyl- Endopeptidase Which Hydrolyzes Peptidoglycan ^,

Yulia Redko, Pascal Courtin, Christine Mézange, Carine Huard, and Marie-Pierre Chapot-Chartier^*

INRA, Unité de Biochimie Bactérienne, UR477, 78350 Jouy en Josas, France

Received 28 March 2007/ Accepted 11 July 2007

YjgB is one of five peptidoglycan hydrolases previously identified in Lactococcus lactis. Analysis of its amino acid sequence revealed that YjgB contains an NlpC/P60 domain, whereas no specific cell wall binding domain or motif could be identified. The NlpC/P60 family is characterized by three conserved residues, a cysteine, a histidine, and a polar residue. In agreement with the presence of a Cys residue in the catalytic site of YjgB, its enzymatic activity was enhanced in the presence of dithiothreitol. Peptidoglycan-hydrolyzing activity of YjgB was detected in growing cells of an L. lactis strain overexpressing YjgB, as revealed by the presence of disaccharide (DS)-dipeptide in the muropeptide composition of the overexpressing strain. YjgB hydrolyzes the peptide chains of L. lactis muropeptides between -D-Gln and L-Lys residues. Its hydrolytic activity was detected on DSs with tetra- and pentapeptide chains, whereas hydrolytic activity was very low on DS-tripeptides. Thus, we demonstrated that YjgB is an endopeptidase which cleaves -D-Gln-L-Lys bonds in peptide chains of L. lactis peptidoglycan.

Published ahead of print on 20 July 2007.

Supplemental material for this article may be found at http://aem.asm.org/.

Present address: CNRS UPR9073, Institut de Biologie Physico-Chimique, 13 rue Pierre et Marie Curie, 75005 Paris, France.

Present address: INRA, Laboratoire des Interactions Plantes Micro- organismes, 31326 Castanet Tolosan Cedex, France.

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