The sequence, structural, and functional diversity within a protein family and implications for specificity and safety: The case for ETX_MTX2 insecticidal proteins

• Published in: Journal of invertebrate pathology Vol. 142; pp. 50 - 59
• Main Authors: Moar, William J., Evans, Adam J., Kessenich, Colton R., Baum, James A., Bowen, David J., Edrington, Thomas C., Haas, Jeffrey A., Kouadio, Jean-Louis K., Roberts, James K., Silvanovich, Andre, Yin, Yong, Weiner, Brian E., Glenn, Kevin C., Odegaard, Matthew L.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01-01-2017
• Subjects: Amino Acid Sequence; Animals; Bacillus thuringiensis; Beta pore forming toxins; Bioinformatics; Computational Biology - methods; Cry51; Endotoxins - chemistry; Endotoxins - classification; Endotoxins - genetics; ETX/MTX2 Pfam; Insecticides - chemistry; Insecticides - classification; Insecticides - metabolism; Lygus; Models, Molecular; Pest Control, Biological - methods; Structure-Activity Relationship; ETX/MTX2 Pfam; Beta pore forming toxins; Cry51; Bioinformatics; Bacillus thuringiensis; Lygus
• ISSN: 0022-2011; 1096-0805
• DOI: 10.1016/j.jip.2016.05.007

[Display omitted]
•Many ETX-MTX2 insecticidal proteins have a lengthy HOSU and consumption.•ETX_MTX2 domains are found in genes and proteins of commonly consumed food species.•Head region diversity and variant selectivity are consistent with specificity and safety.•A domain-based approach should be included when evaluating insecticidal proteins.•A domain-based approach adds value to the weight of evidence safety assessment.
The need for sustainable insect pest control is driving the investigation and discovery of insecticidal proteins outside of the typical 3-domain Cry protein family from Bacillus thuringiensis (Bt). Examples include Cry35 and Cry51 that belong to protein families (Toxin_10, ETX_MTX2) sharing a common β-pore forming structure and function with known mammalian toxins such as epsilon toxin (ETX). Although β-pore forming proteins are related to mammalian toxins, there are key differences in sequence and structure that lead to organism specificity that is useful in the weight-of-evidence approach for safety assessment. Despite low overall amino acid sequence identity among ETX_MTX2 proteins, sequence and structural similarities are found in the tail region responsible for the shared oligomerization and pore formation functions (causing the “relatedness”). Conversely, most of the sequence and structural diversity is located in the head region that is likely responsible for differential receptor binding and target species specificity (e.g., insecticidal vs. mammalian). Therefore, inclusion of a domain-based protein characterization approach that includes bioinformatic and functional comparisons of conserved and diverse domains will enhance the overall weight of evidence safety assessment of proteins including recently reported Cry51 protein variants (Cry51Aa1, Cry51Aa2, and Cry51Aa2.834_16).