A Caenorhabditis elegans Glycolipid-binding Galectin Functions in Host Defense against Bacterial Infection

Keiko Gengyo-Ando,Keiko Fukushima,Katsufumi Dejima,Hiroko Ideo,Shohei Mitani,Kazuya Nomura,Katsuko Yamashita

doi:10.1074/jbc.m109.038257

Abstract

Galectins are a family of beta-galactoside-binding proteins that are widely found among animal species and that regulate diverse biological phenomena. To study the biological function of glycolipid-binding galectins, we purified recombinant Caenorhabditis elegans galectins (LEC-1-11) and studied their binding to C. elegans glycolipids. We found that LEC-8 binds to glycolipids in C. elegans through carbohydrate recognition. It has been reported that Cry5B-producing Bacillus thuringiensis strains can infect C. elegans and that the C. elegans Cry5B receptor molecules are glycolipids. We found that Cry5B and LEC-8 bound to C. elegans glycolipid-coated plates in a dose-dependent manner and that Cry5B binding to glycolipids was inhibited by the addition of LEC-8. LEC-8 is usually expressed strongly in the pharyngeal-intestinal valve and intestinal-rectal valve and is expressed weakly in intestine. However, when C. elegans were fed Escherichia coli expressing Cry5B, intestinal LEC-8::EGFP protein levels increased markedly. In contrast, LEC-8::EGFP expression triggered by Cry5B was reduced in toxin-resistant C. elegans mutants, which had mutations in genes involved in biosynthesis of glycolipids. Moreover, the LEC-8-deficient mutant was more susceptible to Cry5B than wild-type worms. These results suggest that the glycolipid-binding lectin LEC-8 contributes to host defense against bacterial infection by competitive binding to target glycolipid molecules.

Highlights

With glycolipids containing SO3Ϫ33Gal␤133(GalNAc)2 residues [9]
We have clearly demonstrated that C. elegans LEC-8 recognizes glycolipids and functions in host defense against bacterial infection by competition
We have reported previously that human galectin-4 recognizes mammalian sulfated glycolipids, and we speculated that such lectins might function in host defense [9]

Summary

Introduction

With glycolipids containing SO3Ϫ33Gal␤133(GalNAc)2 residues [9]. it is not easy to study the biological functions of this glycolipid-binding lectin because complicated mammalian systems are regulated by many factors and because few models exist for in vivo study. We used the Cry5B toxin, which enters C. elegans intestinal cells through glycolipid receptors, to investigate whether a glycolipid-binding lectin could function in host defense against infection in this study. Rolling worms with LEC-8::EGFP expression were transferred to Cry5B toxin plates and scored under a dissecting microscope.

Results

Conclusion