Peptidoglycan recognition proteins - A novel family of four human innate immunity pattern recognition molecules

The innate immune system recognizes microorganisms through a series of patt ern recognition receptors that are highly conserved in evolution. Insects h ave a family of 12 peptidoglycan recognition proteins (PGRPs) that recogniz e peptidoglycan, a ubiquitous component of bacterial cell walls. We report cloning of three novel human PGRPs (PGRP-L, PGRP-I alpha, and PGRP-I beta) that together with the previously cloned PGRP-S, define a new family of hum an pattern recognition molecules. PGRP-L, PGRP-I alpha, and PGRP-1 beta hav e 576,341, and 373 amino acids coded by five, seven, and eight exons on chr omosomes 19 and 1, and they all have two predicted transmembrane domains. A ll mammalian and insect PGRPs have at least three highly conserved C-termin al PGRP domains located either in the extracellular or in the cytoplasmic ( or in both) portions of the molecules. PGRP-L is expressed in liver, PGRP-I alpha and PGRP-I beta in esophagus (and to a lesser extent in tonsils and thymus), and PGRP-S in bone marrow (and to a lesser extent in neutrophils a nd fetal liver). All four human PGRPs bind peptidoglycan and Grampositive b acteria. Thus, these PGRPs may play a role in recognition of bacteria in th ese organs.