Modified Cry Toxins Bypass Cadherin Receptor Resistance

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Solution Overview

Problem

The development of resistance in insect populations to Cry toxins from Bacillus thuringiensis (Bt) is a significant obstacle, as it reduces the effectiveness of these environmentally friendly insecticides, with resistance often linked to mutations in the cadherin gene that affect receptor binding, rendering insects resistant to wild 3-Domain Cry toxins.

Innovation Solution

Modified 3-Domain Cry toxins are produced by genetic constructions lacking the α-1 helix, which do not require binding to the cadherin receptor for activation and toxicity, thereby bypassing the primary resistance mechanism and maintaining toxicity against resistant insects.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If wild 3-Domain Cry toxins are used to control insects, then they are effective against susceptible insects, but they lose effectiveness against resistant insects due to cadherin receptor mutations

Engineering Contradiction:

Improvetoxin effectivenessVSAvoidresistance to cadherin mutations

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The invention extracts and removes the α-1 helix domain from the Cry toxin structure. This extracted modification allows the toxin to function without requiring binding to the cadherin receptor, thereby bypassing the resistance mechanism while maintaining toxicity against resistant insects

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The invention changes the structural parameter of the toxin by deleting the α-1 helix domain. This parameter change fundamentally alters the toxin's mechanism of action, enabling it to activate and form pores without the cadherin binding step that resistant insects block

Inventive Principle:

Principle #35Parameter changes

2Reliability

If cadherin binding is required for toxin activation, then the toxin mechanism is well-defined, but resistance develops through cadherin gene mutations

Engineering Contradiction:

Improvetoxin activation mechanismVSAvoidresistance development

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

By removing the α-1 helix domain, the invention extracts the cadherin-binding function from the toxin. This allows the remaining toxin structure to activate through alternative mechanisms that do not depend on cadherin receptors, thereby preventing resistance development

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

Instead of requiring cadherin binding to enable toxin activation, the invention inverts the approach by designing a toxin that activates without cadherin binding. The modified toxin uses alternative activation pathways that are not blocked by cadherin mutations

Inventive Principle:

Principle #13The other way round (Inversion)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The Modified 3-Domain Cry toxins effectively kill insects resistant to wild Cry toxins by forming oligomeric pre-pores without needing to bind to the cadherin receptor, thus suppressing resistance and maintaining efficacy against both susceptible and resistant insect strains.

Implementation Method 1

The toxicity of the Modified 3-Domain Cry Toxins was demonstrated against two strains of insects resistant to wild Cry1A toxins and was also tested on insects with a reduced vulnerability to Cry toxins induced by silencing the cadherin RNA

Methodology Applied

Scientific EffectOligomerization:

Implementation Method 2

Binding to cadherin facilitates the proteolytic cut of the α-1 helix of Domain I and the formation of a oligomeric pre-pore which is responsible for the toxicity of these proteins

Methodology Applied

Scientific EffectProteolytic cleavage: Hydrolysis

Data Source

PatentEP2184293B1Suppression of resistance in insects to bacillus thuringiensis cry toxins, using toxins that do not require the cadherin receptor

Publication Date: 2011.10.12 UNIV NAT AUTONOMA DE MEXICO

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AI summary

The invention relates to a method for obtaining DNA constructions coding for Cry toxins with 3 domains (also known as Cry toxins, Bt toxins or δ-endotoxins), which lack helix α-1. Said DNA constructions were modified in order to encode proteins that can kill insects that are resistant to the corresponding non-modified Cry toxins. The invention relates to the DNA constructions of the genes of modified 3-domain Cry toxins and the modified 3-domain Cry proteins, together with methods, molecular vectors and host cells containing said constructions, as well as recombinant methods for producing the modified 3-domain Cry toxins. In addition, the invention relates to formulations containing the modified 3-domain Cry toxins. Resistance of insects to non-modified Cry toxins is due to a reduced binding of the toxin to the receptors in the insect's intestine. More specifically, the invention relates to the expression of the modified 3-domain Cry toxins, the methods for expressing said modified 3-domain Cry toxins, transformed microorganisms and transgenic plants with constructions that express the modified 3-domain Cry toxins and methods for suppressing resistance of pests to non-modified Cry toxins.