Figure 5.

Functions and expression of mammalian PGLYRP proteins. The diagram in the center shows the regions of the human body where each PGLYRP is expressed; note that the information shown applies to other mammals as well as humans. (a) Mammalian PGLYRP-3 has direct bactericidal activity and is expressed in the skin, eyes, tongue, esophagus, stomach, and intestines. (b) PGLYRP-4 and the PGLYRP-3:4 dimer also have direct bactericidal activity in the same tissues; PGLYRP-4 is also expressed in the salivary gland, mucus-secreting glands in the throat and also in saliva. (c) PGLYRP-2, which is constitutively produced in the liver and secreted into the blood, is also induced in the skin and intestine. It is an N-acetylmuramoyl-L-alanine amidase that hydrolyzes proinflammatory peptidoglycan. The structure of Lys-type peptidoglycan is shown, to indicate where in the molecule PGLYRP-2 hydrolyzes it. (d) PGLYRP-1 is present in the granules of the polymorphonuclear leukocytes (PMNs) which are produced in the bone marrow. PGLYRP-1 is bactericidal for phagocytosed bacteria; the images show killing of bacillus by PMNs. The images of scanning electron micrographs of Bacillus in (a) and (b) are copyright Dennis Kunkel Microscopy, Inc and are reproduced with permission. PGLYRP structures were rendered by RasMol and arranged as homodimers or heterodimers. The structure of PGLYRP-1 is based on PDB entry 1yckA; the structure of the carboxy-terminal PGRP domain of PGLYRP-2 was predicted by Swiss-Model on the basis of the crystal structure of D. melanogaster PGRP-SA (PDB entry 1s2jB); the amino-terminal portion of PGLYRP-2 cannot be predicted and hence is shown as an oval; the structures of PGLYRP-3 and PGLYRP-4 were predicted by Swiss-Model based on the crystal structure of carboxy-terminal half of PGLYRP-3 (PDB entry 1SK3A).