title: The pesticidal Cry6Aa toxin from Bacillus thuringiensis is structurally similar to HlyE-family alpha pore-forming toxins.
abstract: The 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.
  
  
  
  The 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.
  
  
  
  Cry6 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.
authors: Shamrock Structures LLC, Woodridge, IL, USA.
authors: Alexey
authors: A
authors: Dementiev
authors: Cardiff School of Biosciences, Cardiff University, Park Place, Cardiff, CF15 8FA, UK.
authors: Jason
authors: J
authors: Board
authors: University of Massachusetts Medical School, 373 Plantation Street, Worcester, MA, 01605-2377, USA.
authors: Anand
authors: A
authors: Sitaram
authors: Dow AgroSciences, LLC, Indianapolis, IN, USA.|Present address: Indiana State Department of Health Laboratories, Indianapolis, IN, USA.
authors: Timothy
authors: T
authors: Hey
authors: Dow AgroSciences, LLC, Indianapolis, IN, USA.|Present address: Xylogenics, LLC, Indianapolis, IN, USA.
authors: Matthew S
authors: MS
authors: Kelker
authors: Dow AgroSciences, LLC, Indianapolis, IN, USA.
authors: Xiaoping
authors: X
authors: Xu
authors: University of Massachusetts Medical School, 373 Plantation Street, Worcester, MA, 01605-2377, USA.
authors: Yan
authors: Y
authors: Hu
authors: Cardiff School of Biosciences, Cardiff University, Park Place, Cardiff, CF15 8FA, UK.|Present address: Laboratorio de Interacción Planta-Insecto, Departamento de Biología Medioambiental, Centro de Investigaciones Biológicas - CSIC, Madrid, Spain.
authors: Cristian
authors: C
authors: Vidal-Quist
authors: Dow AgroSciences, LLC, Indianapolis, IN, USA.
authors: Vimbai
authors: V
authors: Chikwana
authors: Dow AgroSciences, LLC, Indianapolis, IN, USA.
authors: Samantha
authors: S
authors: Griffin
authors: Dow AgroSciences, LLC, Indianapolis, IN, USA.
authors: David
authors: D
authors: McCaskill
authors: Dow AgroSciences, LLC, Indianapolis, IN, USA.
authors: Nick X
authors: NX
authors: Wang
authors: 6125 Londonberrie Ct., Midland, MI, 48640, USA.
authors: Shao-Ching
authors: SC
authors: Hung
authors: School of Life Sciences and Center of Novel Biomaterials, The Chinese University of Hong Kong, Shatin, HK SAR, China.
authors: Michael K
authors: MK
authors: Chan
authors: School of Life Sciences and Center of Novel Biomaterials, The Chinese University of Hong Kong, Shatin, HK SAR, China.
authors: Marianne M
authors: MM
authors: Lee
authors: Cardiff School of Biosciences, Cardiff University, Park Place, Cardiff, CF15 8FA, UK.|Present address: Antimicrobial Reference Laboratory, Southmead Hospital, Westbury-on-Trym, Bristol, BS10 5NB, UK.
authors: Jessica
authors: J
authors: Hughes
authors: Cardiff School of Biosciences, Cardiff University, Park Place, Cardiff, CF15 8FA, UK.
authors: Alice
authors: A
authors: Wegener
authors: University of Massachusetts Medical School, 373 Plantation Street, Worcester, MA, 01605-2377, USA.
authors: Raffi V
authors: RV
authors: Aroian
authors: Dow AgroSciences, LLC, Indianapolis, IN, USA.
authors: Kenneth E
authors: KE
authors: Narva
authors: Cardiff School of Biosciences, Cardiff University, Park Place, Cardiff, CF15 8FA, UK. Berry@cf.ac.uk.
authors: Colin
authors: 0000-0002-9943-548X
authors: C
authors: Berry
mesh_terms: D000818:Animals; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins / Q000737:chemistry* / Q000633:toxicity*; D001681:Biological Assay; D017173:Caenorhabditis elegans / Q000187:drug effects; D018360:Crystallography, X-Ray; D004220:Disulfides / Q000378:metabolism; D004731:Endotoxins / Q000737:chemistry* / Q000633:toxicity*; D006460:Hemolysin Proteins / Q000737:chemistry* / Q000633:toxicity*; D008958:Models, Molecular; D010575:Pesticides / Q000737:chemistry / Q000633:toxicity*; D052899:Pore Forming Cytotoxic Proteins / Q000737:chemistry*; D011487:Protein Conformation; D040681:Structural Homology, Protein; D014357:Trypsin / Q000378:metabolism
chemical_list: D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D004220:Disulfides; D004731:Endotoxins; D006460:Hemolysin Proteins; D010575:Pesticides; D052899:Pore Forming Cytotoxic Proteins; C030956:insecticidal crystal protein, Bacillus Thuringiensis; D014357:Trypsin
keywords: Bacillus thuringiensis; Cry6; Hemolysin; Insecticidal toxin