C-type lectins from the nematode parasites Heligmosomoides polygyrus and Nippostrongylus brasiliensis

Yvonne Harcus,Gavin Nicoll,Janice Murray,Kara Filbey,Natalia Gomez-Escobar,Rick M Maizels

doi:10.1016/j.parint.2009.08.011

Abstract

The C-type lectin superfamily is highly represented in all metazoan phyla so far studied. Many members of this superfamily are important in innate immune defences against infection, while others serve key developmental and structural roles. Within the superfamily, many proteins contain multiple canonical carbohydrate-recognition domains (CRDs), together with additional non-lectin domains. In this report, we have studied two gastrointestinal nematode parasites which are widely used in experimental rodent systems, Heligmosomoides polygyrus and Nippostrongylus brasiliensis. From cDNA libraries, we have isolated 3 new C-type lectins from these species; all are single-CRD proteins with short additional N-terminal domains. The predicted Hp-CTL-1 protein contains 156 aa, Nb-CTL-1 191 aa and Nb-CTL-2 183 aa; all encode predicted signal peptides, as well as key conserved sequence motifs characteristic of the CTL superfamily. These lectins are most similar to C. elegans CLEC-48, 49 and 50, as well as to the lectin domains of mammalian immune system proteins CD23 and CD206. RT-PCR showed that these H. polygyrus and N. brasiliensis genes are primarily expressed in the gut-dwelling adult stages, although Nb-CTL-2 transcripts are also prominent in the free-living infective larval (L3) stage. Polyclonal antibodies raised to Hp-CTL-1 and Nb-CTL-1 reacted to both proteins by ELISA, and in Western blot analysis recognised a 15-kDa band in secreted proteins of adult N. brasiliensis (NES) and a 19-kDa band in H. polygyrus ES (HES). Anti-CTL-1 antibody also bound strongly to the cuticle of adult H. polygyrus. Hence, live parasites release C-type lectins homologous to some key receptors of the mammalian host immune system, raising the possibility that these products interfere in some manner with immunological recognition or effector function.

Highlights

The C-type lectin (CTL) superfamily has emerged as one of the largest and most widely expressed set of proteins among metazoan organisms in general [1,2]
From an adult H. polygyrus cDNA library, we identified Hp-CTL-1 as a full-length transcript encoding a 22aa predicted signal peptide and a 135-aa single-domain carbohydrate-recognition domains (CRDs) (Fig. 1), with a predicted mature mol.wt. of 17,811 before signal peptide cleavage is taken into account
It was noted that minor sequence variants were present in different clones from the cDNA library of N. brasiliensis, indicating some degree of polymorphism at these gene loci; similar minor variation has been noted with CTL sequences from the tissue-dwelling nematode Toxocara canis [39]

Summary

Introduction

The C-type lectin (CTL) superfamily has emerged as one of the largest and most widely expressed set of proteins among metazoan organisms in general [1,2]. They are characterized by a conserved 115–130 amino acid carbohydrate-recognition domain (CRD) which includes multiple Ca2+-binding sites, which determine the calcium (C-type) dependency of ligation. They contain 4 critical cysteine residues which stabilise a two-loop structure, with the key residues involved in sugar binding located on a long flexible loop.

Methods

Results

Conclusion