Recombinant Human PGLYRP1/PGRP-S Protein

The human PGRP family is comprised of four peptidoglycan recognition proteins that may function as innate immunity pattern recognition molecules (1, 2). Termed PGRP-L, PGRP-I alpha, PGRP-I beta and PGRP-S, they are all products of separate genes, and all are named for the relative length of their translated product (3). PGRP-L (for long) is 576 amino acids (aa) in length, while PGRP-I alpha and I beta are (I) intermediate in length at 341 aa and 373 aa, respectively, and PGRP-S is the shortest at 196 aa in length (3, 4). All human PGRPs bind peptidoglycan and Gram-positive bacteria, and all have at least three C-terminal PGRP domains at variable sites that are highly conserved from insects to mammals (3). Human PGRP-S, the first described member of the family, is a 28 kDa secreted glycoprotein associated with neutrophils (4). The mature molecule is 175 aa in length and contains three variably-sized peptide-carbohydrate recognition sequences of 15 aa, 29 aa and 49 aa, respectively. Human PGRP-S is 72%, 71% and 70% aa identical to mouse, bovine and rat mature PGRP-S, respectively. Studies with PGRP-S deficient mice indicate that knock-out mice have increased susceptibility to infections with non-pathogenic bacteria. Neutrophils from knock-out mice exhibit normal phagocytosis of bacteria but are defective in intracellular killing and digestion of nonpathogenic bacteria (5). The longer three PGRP members are all membrane-bound molecules that contain two membrane-spanning segments. Both the N- and C-termini are depicted as being extracellular with a joining cytoplasmic domain. All three transmembrane forms show at least one PGRP domain on the C-terminal extracellular region; other PGRP domains are variably distributed over their two extracellular and one cytoplasmic region (3).