Human Intelectin Is a Novel Soluble Lectin That Recognizes Galactofuranose in Carbohydrate Chains of Bacterial Cell Wall

Shoutaro Tsuji,Junji Uehori,Misako Matsumoto,Yasuhiko Suzuki,Akio Matsuhisa,Kumao Toyoshima,Tsukasa Seya

doi:10.1074/jbc.m103162200

Abstract

Galactofuranosyl residues are present in various microorganisms but not in mammals. In this study, we identified a human lectin binding to galactofuranosyl residues and named this protein human intelectin (hIntL). The mature hIntL was a secretory glycoprotein consisting of 295 amino acids and N-linked oligosaccharides, and its basic structural unit was a 120-kDa homotrimer in which 40-kDa polypeptides were bridged by disulfide bonds. The hIntL gene was split into 8 exons on chromosome 1q21.3, and hIntL mRNA was expressed in the heart, small intestine, colon, and thymus. hIntL showed high levels of homology with mouse intelectin, Xenopus laevis cortical granule lectin/oocyte lectin, lamprey serum lectin, and ascidian galactose-specific lectin. These homologues commonly contained no carbohydrate recognition domain, which is a characteristic of C-type lectins, although some of them have been reported as Ca(2+)-dependent lectins. Recombinant hIntL revealed affinities to d-pentoses and a d-galactofuranosyl residue in the presence of Ca(2+), and recognized the bacterial arabinogalactan of Nocardia containing d-galactofuranosyl residues. These results suggested that hIntL is a new type lectin recognizing galactofuranose, and that hIntL plays a role in the recognition of bacteria-specific components in the host.

Highlights

Galactofuranosyl residues are present in various microorganisms but not in mammals
Recombinant human intelectin (hIntL) revealed affinities to D-pentoses and a D-galactofuranosyl residue in the presence of Ca2؉, and recognized the bacterial arabinogalactan of Nocardia containing D-galactofuranosyl residues. These results suggested that hIntL is a new type lectin recognizing galactofuranose, and that hIntL plays a role in the recognition of bacteria-specific components in the host
We purified a novel human galactosebinding lectin and cloned its cDNA. We demonstrated that this lectin, human intelectin, is a new type of Ca2ϩ-dependent lectin that has affinity to galactofuranosyl residues and recognizes bacterial arabinogalactan

Summary

EXPERIMENTAL PROCEDURES

Galactose-Sepharose—Galactose-Sepharose was produced by incubating epoxy-activated Sepharose 6B (Amersham Pharmacia Biotech) with galactose according to the manufacturer’s instructions. Several bands were cut out from the PVDF membranes stained with Coomassie Blue, and the strips were treated with 0.6 M HCl for 24 h at 25 °C (deblocking of formylation) and stored at Ϫ20 °C. These procedures were repeated five times and the strips were used for N-terminal amino acid sequence analysis. Northern Blotting—The MTN blot membranes containing 2 ␮g of poly(A)ϩ RNA from various human tissues (CLONTECH) were hybridized at 65 °C for 1 h in ExpressHyb hybridization solution (CLONTECH) with 32P-labeled cDNA of open reading frame sequences of hIntL. 1 mg of recombinant human intelectin (rhIntL) was purified from 700 ml of culture supernatant by galactose-Sepharose column chromatography

Human Intelectin Recognizes Galactofuranosyl Residue

RESULTS

DISCUSSION