Helix pomatia Lectin, an Inducer of Drosophila Immune Response, Binds to Hemomucin, a Novel Surface Mucin

Ulrich Theopold,Christos Samakovlis,Hediye Erdjument-Bromage,Natalie Dillon,Bernt Axelsson,Otto Schmidt,Paul Tempst,Dan Hultmark

doi:10.1074/jbc.271.22.12708

Abstract

We describe the isolation and initial characterization of hemomucin, a novel Drosophila surface mucin that is likely to be involved in the induction of antibacterial effector molecules after binding a snail lectin (Helix pomatia A hemagglutinin). Two proteins of 100 and 220 kDa were purified from the membrane fraction of a Drosophila blood cell line using lectin columns. The two proteins are products of the same gene, as demonstrated by peptide sequencing. The corresponding cDNAs code for a product that contains an amino-terminal putative transmembrane domain, a domain related to the plant enzyme strictosidine synthase, and a mucin-like domain in the carboxyl-terminal part of the protein. The gene is expressed throughout development. In adult flies, high expression is found in hemocytes, in specialized regions of the gut, and in the ovary, where the protein is deposited onto the egg surface. In the gut, the mucin co-localizes with the peritrophic membrane. The cytogenetic location of the gene is on the third chromosome in the region 97F-98A.

Highlights

Named surface mucins have been described in the vertebrate immune system (10)
The H.p. lectindependent induction could be inhibited by GalNAc, the sugar known to inhibit H.p. lectin binding to human leukocytes (Fig. 1B), showing that the induction is not due to nonlectin contaminants in the H.p. lectin preparation
We describe here the isolation and initial characterization of hemomucin, a novel cell surface molecule from a Drosophila hemocyte cell line

Summary

Introduction

They participate in the initial attachment of leukocytes during inflammatory responses, which leads to the migration toward the site of inflammation (11) This function is facilitated by a specialized structure common to surface mucins, i.e., highly O-glycosylated protein domains separated by proline residues (12) that inhibit the formation of a globular structure. Heterologous lectins have been shown to label structures on the cell surfaces of Drosophila hemocytes (18, 19), giving rise to a phenotype that was described as “speckled.” The number of speckled cells increased in flies after immune stimulation with heterospecific implants as well as in flies with melanotic tumors (19) These and other findings (20) suggest that the pro-

Methods

Results

Conclusion