An anhydro-N-acetylmuramyl-L-alanine amidase with broad specificity tethered to the outer membrane of Escherichia coli.
From its amino acid sequence homology with AmpD, we recognized YbjR, now renamed AmiD, as a possible second 1,6-anhydro-N-acetylmuramic acid (anhMurNAc)-l-alanine amidase in Escherichia coli. We have now confirmed that AmiD is an anhMurNAc-l-Ala amidase and demonstrated that AmpD and AmiD are the only enzymes present in E. coli that are able to cleave the anhMurNAc-l-Ala bond. The activity was present only in the outer membrane fraction obtained from an ampD mutant. In contrast to AmpD, which is specific for the anhMurNAc-l-alanine bond, AmiD also cleaved the bond between MurNAc and l-alanine in both muropeptides and murein sacculi. Unlike the periplasmic murein amidases, AmiD did not participate in cell separation. ampG mutants, which are unable to import GlcNAc-anhMurNAc-peptides into the cytoplasm, released mainly peptides into the medium due to AmiD activity, whereas an ampG amiD double mutant released a large amount of intact GlcNAc-anhMurNAc-peptides into the medium.
Uehara
Tsuyoshi
T
Department of Molecular Biology and Microbiology, Tufts University School of Medicine, Boston, MA 02111, USA. tsuyoshi.uehara@tufts.edu
Park
James T
JT
D000595:Amino Acid Sequence; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000737:chemistry*; D004926:Escherichia coli / Q000737:chemistry* / Q000201:enzymology* / Q000235:genetics; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism; D017353:Gene Deletion; D008969:Molecular Sequence Data; D009154:Mutation; D009238:N-Acetylmuramoyl-L-alanine Amidase / Q000235:genetics / Q000378:metabolism*; D010457:Peptidoglycan / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity
D001425:Bacterial Outer Membrane Proteins; D029968:Escherichia coli Proteins; D010457:Peptidoglycan; D009238:N-Acetylmuramoyl-L-alanine Amidase