AmiD

__**AmiD: An Outer Membrane Anhydro-//N//-Acetylmuramyl-L-Ala Amidase**__

AmiD is an outer membrane anhydro-N-acetylmuramyl-L-Ala amidase. It is one of only two enzymes in E. coli able to cleave the anhMur-NAc-L-Ala bond (the other being AmpD).

It requires zinc for activity.

AmiD is a lipoprotein, i.e. a protein containing both proteins and lipids. The //amiD// gene product contains a short signal sequence and a lipobox motif, followed by Ala, suggesting it is a lipoprotein destined for the outer membrane.Indeed AmiD amidase activity has been demonstrated to be present in the outer membrane.

Substrate specificity: AmiD cleaves the anhMurNAc-L-Ala bond between the disaccharide (GlcNAc-anhMurNAc) and tripeptide (L-Ala-D-Glu-meso-Dap).

It cleaves the anhMurNAc-L-Ala bond in GlcNAc-anhMurNAc-tripeptide much more rapidly than the anhMurNAc-tripeptide. Muropeptides lacking the anhydro ring were also good substrates and peptidoglycan itself was cleaved by the enzyme.