BackgroundThe Cry6 family of proteins from Bacillus thuringiensis represents a group of powerful toxins with great potential for use in the control of coleopteran insects and of nematode parasites of importance to agriculture. These proteins are unrelated to other insecticidal toxins at the level of their primary sequences and the structure and function of these proteins has been poorly studied to date. This has inhibited our understanding of these toxins and their mode of action, along with our ability to manipulate the proteins to alter their activity to our advantage. To increase our understanding of their mode of action and to facilitate further development of these proteins we have determined the structure of Cry6Aa in protoxin and trypsin-activated forms and demonstrated a pore-forming mechanism of action.ResultsThe two forms of the toxin were resolved to 2.7 Å and 2.0 Å respectively and showed very similar structures. Cry6Aa shows structural homology to a known class of pore-forming toxins including hemolysin E from Escherichia coli and two Bacillus cereus proteins: the hemolytic toxin HblB and the NheA component of the non-hemolytic toxin (pfam05791). Cry6Aa also shows atypical features compared to other members of this family, including internal repeat sequences and small loop regions within major alpha helices. Trypsin processing was found to result in the loss of some internal sequences while the C-terminal region remains disulfide-linked to the main core of the toxin. Based on the structural similarity of Cry6Aa to other toxins, the mechanism of action of the toxin was probed and its ability to form pores in vivo in Caenorhabditis elegans was demonstrated. A non-toxic mutant was also produced, consistent with the proposed pore-forming mode of action.ConclusionsCry6 proteins are members of the alpha helical pore-forming toxins – a structural class not previously recognized among the Cry toxins of B. thuringiensis and representing a new paradigm for nematocidal and insecticidal proteins. Elucidation of both the structure and the pore-forming mechanism of action of Cry6Aa now opens the way to more detailed analysis of toxin specificity and the development of new toxin variants with novel activities.Electronic supplementary materialThe online version of this article (doi:10.1186/s12915-016-0295-9) contains supplementary material, which is available to authorized users.

Understanding of proteins and other biological macromolecules must be based on an appreciation of their 3-dimensional shape and the fine details of their structure. Conveying these details in a clear and stimulating fashion can present challenges using conventional approaches and 2-dimensional monitors and projectors. Here we describe a method for the production of 3-D interactive images of protein structures that can be manipulated in real time through the use of augmented reality software. Users first see a real-time image of themselves using the computer's camera, then, when they hold up a trigger image, a model of a molecule appears automatically in the video. This model rotates and translates in space in response to movements of the trigger card. The system described has been optimized to allow customization for the display of userselected structures to create engaging, educational visualizations to explore 3-D structures. V C 2014 by The International Union of Biochemistry and Molecular Biology, 42(5): 446-449, 2014.

Homology modelling can provide important insights into the structures of proteins when a related protein structure has already been solved. However, for many proteins, including a number of invertebrate-active toxins and accessory proteins, no such templates exist. In these cases, techniques of ab initio, template-independent modelling can be employed to generate models that may give insight into structure and function. In this overview, examples of both the problems and the potential benefits of ab initio techniques are illustrated. Consistent modelling results may indicate useful approximations to actual protein structures and can thus allow the generation of hypotheses regarding activity that can be tested experimentally.