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A macrophage protein, Ym1, transiently expressed during inflammation is a novel mammalian lectin
1Institute of Microbiology and Immunology, National Yang-Ming University, Taipei, Taiwan 112, Republic of China. acchang@ym.edu.tw
Abstract:
Oral infections of mice with Trichinella spiralis induce activation of peritoneal exudate cells to transiently express and secrete a crystallizable protein Ym1. Purification of Ym1 to homogeneity was achieved. It is a single chain polypeptide (45 kDa) with a strong tendency to crystallize at its isoelectric point (pI 5.7). Co-expression of Ym1 with Mac-1 and scavenger receptor pinpoints macrophages as its main producer. Protein microsequencing data 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 secretory protein was deduced and later deposited in GenBank (accession number M94584) in 1992. By means of surface plasmon resonance analyses, Ym1 has been shown to exhibit binding specificity to saccharides with a free amine group, such as GlcN, GalN, or GlcN polymers, but it failed to bind to other saccharides. The interaction is pH-dependent but Ca2+ and Mg2+ ion-independent. The binding avidity of Ym1 to GlcN oligosaccharides was enhanced by more than 1000-fold due to the clustering effect. Specific binding of Ym1 to heparin suggests that heparin/heparan sulfate may be its physiological ligand in vivo during inflammation and/or tissue remodeling. Although it shares approximately 30% homology with microbial chitinases, no chitinase activity was found associated with Ym1. Genomic Southern blot analyses suggest that Ym1 may represent a member of a novel lectin gene family.
Insights
The protein Ym1, secreted by macrophages during Trichinella spiralis infection, binds specifically to certain saccharides like N-acetylglucosamine. This crystallizable protein may represent a novel lectin involved in inflammation and tissue remodeling.
Area of Science:
- Immunology
- Biochemistry
- Molecular Biology
Background:
- Trichinella spiralis infection in mice triggers the expression of a unique protein, Ym1.
- Ym1 is a crystallizable, 45 kDa polypeptide secreted by activated peritoneal exudate cells, primarily macrophages.
Purpose of the Study:
- To purify and characterize Ym1.
- To determine the cDNA sequence and identify Ym1's binding specificities and potential physiological role.
Main Methods:
- Protein purification and microsequencing.
- cDNA cloning and sequencing.
- Surface plasmon resonance analysis to assess saccharide binding.
- Genomic Southern blot analysis.
Main Results:
- Ym1 was purified to homogeneity and its full-length cDNA was cloned.
- Ym1 exhibits specific binding to saccharides with free amine groups (e.g., N-acetylglucosamine) and heparin.
- Binding is pH-dependent and Ca2+/Mg2+ independent, with enhanced avidity for oligosaccharides.
- No chitinase activity was detected, despite homology to chitinases.
Conclusions:
- Ym1 is a novel macrophage-secreted protein with specific carbohydrate-binding properties.
- Ym1 likely functions as a lectin, potentially binding heparin/heparan sulfate in vivo.
- It may play a role in inflammatory responses and tissue remodeling, representing a new lectin gene family.