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Published on: May 26, 2011
Involvement of N-glycans in binding of Photorhabdus luminescens Tc toxin
Peter Njenga Ng'ang'a1,2, Lina Siukstaite3,4, Alexander E Lang1
1Institute for Experimental and Clinical Pharmacology and Toxicology, Faculty of Medicine, University of Freiburg, Freiburg, Germany.
Abstract:
Photorhabdus luminescens Tc toxins are large tripartite ABC-type toxin complexes, composed of TcA, TcB and TcC proteins. Tc toxins are widespread and have shown a tropism for a variety of targets including insect, mammalian and human cells. However, their receptors and the specific mechanisms of uptake into target cells remain unknown. Here, we show that the TcA protein TcdA1 interacts with N-glycans, particularly Lewis X/Y antigens. This is confirmed using N-acetylglucosamine transferase I (Mgat1 gene product)-deficient Chinese hamster ovary (CHO) Lec1 cells, which are highly resistant to intoxication by the Tc toxin complex most likely due to the absence of complex N-glycans. Restoring Mgat1 gene activity, and hence complex N-glycan biosynthesis, recapitulated the sensitivity of these cells to the toxin. Exogenous addition of Lewis X trisaccharide partially inhibits intoxication in wild-type cells. Additionally, sialic acid also largely reduced binding of the Tc toxin. Moreover, proteolytic activation of TcdA1 alters glycan-binding and uptake into target cells. The data suggest that TcdA1-binding is most likely multivalent, and carbohydrates probably work cooperatively to facilitate binding and intoxication.
Insights
Photorhabdus luminescens Tc toxins bind to N-glycans, like Lewis X/Y antigens, on target cells. This interaction is crucial for toxin uptake and intoxication, with sialic acid reducing binding.
Area of Science:
- Microbiology
- Molecular Biology
- Glycobiology
Background:
- Photorhabdus luminescens Tc toxins are tripartite ABC-type complexes.
- These toxins target insect, mammalian, and human cells, but receptors and uptake mechanisms are unknown.
Purpose of the Study:
- To identify the receptors and understand the uptake mechanisms of Photorhabdus luminescens Tc toxins.
Main Methods:
- Utilized N-acetylglucosamine transferase I (Mgat1)-deficient Chinese hamster ovary (CHO) Lec1 cells.
- Assessed toxin sensitivity and binding after restoring Mgat1 gene activity.
- Investigated the effect of Lewis X trisaccharide and sialic acid on intoxication.
- Examined the impact of proteolytic activation on TcdA1 binding and uptake.
Main Results:
- TcdA1 protein interacts with N-glycans, specifically Lewis X/Y antigens.
- Mgat1-deficient CHO Lec1 cells, lacking complex N-glycans, showed high resistance to Tc toxin.
- Restoring Mgat1 gene activity restored toxin sensitivity.
- Lewis X trisaccharide partially inhibited intoxication, while sialic acid reduced toxin binding.
- Proteolytic activation altered TcdA1 glycan-binding and cellular uptake.
Conclusions:
- N-glycans, particularly Lewis X/Y antigens, are likely receptors for Photorhabdus luminescens Tc toxins.
- Carbohydrate binding appears multivalent and cooperative, facilitating toxin binding and intoxication.
- Sialic acid may play a role in modulating toxin interaction with target cells.
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