Tsetse salivary glycoproteins are modified with paucimannosidic N-glycans, are recognised by C-type lectins and bind to trypanosomes

Author summary In addition to helping the ingestion of a bloodmeal, the saliva of vector insects can modulate vertebrate immune responses. However, most research has focused on the salivary proteins, while the sugars (glycans) that modify them remain unexplored. Here we studied N-glycosylation, a common post-translational modification where sugar structures are attached to specific sites of a protein. Insect salivary N-glycans may affect how the saliva is recognized by the host, possibly playing a role during pathogen transmission. In this manuscript, we present the first detailed structural characterization of the salivary N-glycans in the tsetse fly Glossina morsitans, vector of African trypanosomiasis. We found that tsetse fly glycoproteins are mainly modified by simple N-glycans with short mannose modifications, which are recognised by mammalian C-type lectins (mannose receptor and DC-SIGN). Furthermore, we show that salivary glycoproteins bind to the surface of the trypanosomes that are transmitted to the vertebrate host; this opens up interesting questions as to the role of these glycoproteins in the successful establishment of infection by this parasite. Overall, our work represents a novel contribution towards the salivary N-glycome of an important insect vector, and towards the understanding of vector saliva and its complex effects in the vertebrate host. African sleeping sickness is caused by Trypanosoma brucei, a parasite transmitted by the bite of a tsetse fly. Trypanosome infection induces a severe transcriptional downregulation of tsetse genes encoding for salivary proteins, which reduces its anti-hemostatic and anti-clotting properties. To better understand trypanosome transmission and the possible role of glycans in insect bloodfeeding, we characterized the N-glycome of tsetse saliva glycoproteins. Tsetse salivary N-glycans were enzymatically released, tagged with either 2-aminobenzamide (2-AB) or procainamide, and analyzed by HILIC-UHPLC-FLR coupled online with positive-ion ESI-LC-MS/MS. We found that the N-glycan profiles of T. brucei-infected and naive tsetse salivary glycoproteins are almost identical, consisting mainly (>50%) of highly processed Man(3)GlcNAc(2) in addition to several other paucimannose, high mannose, and few hybrid-type N-glycans. In overlay assays, these sugars were differentially recognized by the mannose receptor and DC-SIGN C-type lectins. We also show that salivary glycoproteins bind strongly to the surface of transmissible metacyclic trypanosomes. We suggest that although the repertoire of tsetse salivary N-glycans does not change during a trypanosome infection, the interactions with mannosylated glycoproteins may influence parasite transmission into the vertebrate host.

Publication year:2021

Keywords:A1 Journal article

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BOF-publication weight:3

CSS-citation score:1

Authors:International

Authors from:Government

Accessibility:Open