Peptidoglycan recognition proteins (PGRPs) are pattern recognition receptors that bind, and in certain cases, hydrolyze peptidoglycans (PGNs) of bacterial cell walls. PGRPs have been divided into three classes: short PGRPs (PGRP-S), that are small (20 kDa) extracellular proteins; intermediate PGRPs (PGRP-I) that are 40-45 kDa and are predicted to be transmembrane proteins; and long PGRPs (PGRP-L), up to 90 kDa, which may be either intracellular or transmembrane. Several structures of PGRPs are known in insects and mammals, some bound with substrates like Muramyl Tripeptide (MTP) or Tracheal Cytotoxin (TCT). The substrate binding site is conserved in PGRP-LCx, PGRP-LE, and PGRP-Ialpha proteins. This family includes Zn-dependent N-Acetylmuramoyl-L-alanine Amidase, EC:3.5.1.28. This enzyme cleaves the amide bond between N-acetylmuramoyl and L-amino acids, preferentially D-lactyl-L-Ala, in bacterial cell walls. The structure for the bacteriophage T7 lysozyme shows that two of the conserved histidines and a cysteine are zinc binding residues. Site-directed mutagenesis of T7 lysozyme indicates that two conserved residues, a Tyr and a Lys, are important for amidase activity.

N-acetylmuramoyl-L-alanine amidase. This family includes zinc amidases that have N-acetylmuramoyl-L-alanine amidase activity EC:3.5.1.28. This enzyme domain cleaves the amide bond between N-acetylmuramoyl and L-amino acids in bacterial cell walls (preferentially: D-lactyl-L-Ala). The structure is known for the bacteriophage T7 structure and shows that two of the conserved histidines are zinc binding.

Ami_2 domain.

Sporulation related domain. This 70 residue domain is composed of two 35 residue repeats found in proteins involved in sporulation and cell division such as FtsN, DedD, and CwlM. This domain is involved in binding peptidoglycan. Two tandem repeats fold into a pseudo-2-fold symmetric single-domain structure containing numerous contacts between the repeats. FtsN is an essential cell division protein with a simple bitopic topology, a short N-terminal cytoplasmic segment fused to a large carboxy periplasmic domain through a single transmembrane domain. These repeats lay at the periplasmic C-terminus. FtsN localizes to the septum ring complex.

Sporulation related domain. This 70 residue domain is composed of two 35 residue repeats found in proteins involved in sporulation and cell division such as FtsN, DedD, and CwlM. This domain is involved in binding peptidoglycan. Two tandem repeats fold into a pseudo-2-fold symmetric single-domain structure containing numerous contacts between the repeats. FtsN is an essential cell division protein with a simple bitopic topology, a short N-terminal cytoplasmic segment fused to a large carboxy periplasmic domain through a single transmembrane domain. These repeats lay at the periplasmic C-terminus. FtsN localizes to the septum ring complex.