Preprint Article Version 1 This version is not peer-reviewed

Specificity of Escherichia coli Heat-Labile Enterotoxin Investigated by Single-Site Mutagenesis

Version 1 : Received: 18 December 2018 / Approved: 19 December 2018 / Online: 19 December 2018 (16:20:44 CET)
Version 2 : Received: 28 January 2019 / Approved: 28 January 2019 / Online: 28 January 2019 (15:23:24 CET)

How to cite: Heggelund, J.E.; Heim, J.B.; Bajc, G.; Hodnik, V.; Anderluh, G.; Krengel, U. Specificity of Escherichia coli Heat-Labile Enterotoxin Investigated by Single-Site Mutagenesis. Preprints 2018, 2018120236 (doi: 10.20944/preprints201812.0236.v1). Heggelund, J.E.; Heim, J.B.; Bajc, G.; Hodnik, V.; Anderluh, G.; Krengel, U. Specificity of Escherichia coli Heat-Labile Enterotoxin Investigated by Single-Site Mutagenesis. Preprints 2018, 2018120236 (doi: 10.20944/preprints201812.0236.v1).

Abstract

Diarrhoea caused by enterotoxigenic Escherichia coli is one of the leading causes of mortality in children under five years of age and is a great burden on developing countries. The major virulence factor of the bacterium is the heat-labile enterotoxin (LT), a close homologue of the cholera toxin. The toxins bind to carbohydrate receptors in the gastrointestinal tract, leading to toxin uptake and, ultimately, to severe diarrhoea. Previously, LT from human- and porcine-infecting ETEC (hLT and pLT, respectively) were shown to have different carbohydrate-binding specificities, in particular with respect to N-acetyllactosamine-terminating glycosphingolipids. Here, we probed eleven single-residue variants of the heat-labile enterotoxin with surface plasmon resonance spectroscopy and compared the data to the parent toxins. In addition we present a 1.45 Å crystal structure of pLTB in complex with branched Lacto-N-neohexaose (Galb4GlcNAcb6[Galb4GlcNAcb3]Galb4Glc). The largest difference in binding specificity is caused by mutation of residue 94, which links the primary and secondary binding sites of the toxins. Residue 95 (and to a smaller extent also residues 7 and 18) also contribute, whereas residue 4 shows no effect on monovalent binding of the ligand and may rather be important for multivalent binding, enhancing avidity.

Subject Areas

bacterial toxin; cholera toxin; Escherichia coli heat-labile enterotoxin; lectin; N-acetyllactosamine binding; neutral glycosphingolipids; protein-carbohydrate interactions; surface plasmon resonance; X-ray crystal structure

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