A macrophage protein, Ym1, transiently expressed during inflammation is a novel mammalian lectin

Oral infections of mice with Trichinella spiralis induce activation of peri toneal exudate cells to transiently express and secrete a crystallizable pr otein Ym1, Purification of Ym1 to homogeneity was achieved. It is a single chain polypeptide (45 kDa) with a strong tendency to crystallize at its iso electric point (PI 5.7). Coexpression of Ym1 with Mac-1 and scavenger recep tor pinpoints macrophages as its main producer. Protein microsequencing dat a provide information required for full-length cDNA cloning from libraries constructed from activated peritoneal exudate cells. A single open reading frame of 398 amino acids with a leader peptide (21 residues) typical of sec retory protein was deduced and later deposited in GenBank (TM) (accession n umber M94584) in 1992, By means of surface plasmon resonance analyses, Ym1 has been shown to exhibit binding specificity to saccharides with a free am ine group, such as GlcN, GalN, or GlcN polymers, but it failed to bind to o ther saccharides, The interaction is pH-dependent but Ca2+ and Mg2+ ion-ind ependent. The binding avidity of Ym1 to GlcN oligosaccharides was enhanced by more than 1000-fold due to the clustering effect. Specific binding of Ym 1 to heparin suggests that heparin/heparan sulfate may be its physiological ligand in vivo during inflammation and/or tissue remodeling. Although it s hares similar to 30% homology with microbial chitinases, no chitinase activ ity was found associated with Ym1. Genomic Southern blot analyses suggest t hat Ym1 may represent a member of a novel lectin gene family.