title: Improving Cry8Ka toxin activity towards the cotton boll weevil (Anthonomus grandis).
abstract: BACKGROUND
  The cotton boll weevil (Anthonomus grandis) is a serious insect-pest in the Americas, particularly in Brazil. The use of chemical or biological insect control is not effective against the cotton boll weevil because of its endophytic life style. Therefore, the use of biotechnological tools to produce insect-resistant transgenic plants represents an important strategy to reduce the damage to cotton plants caused by the boll weevil. The present study focuses on the identification of novel molecules that show improved toxicity against the cotton boll weevil. In vitro directed molecular evolution through DNA shuffling and phage display screening was applied to enhance the insecticidal activity of variants of the Cry8Ka1 protein of Bacillus thuringiensis.
  
  
  RESULTS
  Bioassays carried out with A. grandis larvae revealed that the LC50 of the screened mutant Cry8Ka5 toxin was 3.15-fold higher than the wild-type Cry8Ka1 toxin. Homology modelling of Cry8Ka1 and the Cry8Ka5 mutant suggested that both proteins retained the typical three-domain Cry family structure. The mutated residues were located mostly in loops and appeared unlikely to interfere with molecular stability.
  
  
  CONCLUSIONS
  The improved toxicity of the Cry8Ka5 mutant obtained in this study will allow the generation of a transgenic cotton event with improved potential to control A. grandis.
authors: Embrapa Recursos Genéticos e Biotecnologia, PqEB- Final W5 Norte -Brasília, DF, Brasil.
authors: Gustavo R
authors: GR
authors: Oliveira
authors: Maria C M
authors: MC
authors: Silva
authors: Wagner A
authors: WA
authors: Lucena
authors: Erich Y T
authors: EY
authors: Nakasu
authors: Alexandre A P
authors: AA
authors: Firmino
authors: Magda A
authors: MA
authors: Beneventi
authors: Djair S L
authors: DS
authors: Souza
authors: José E
authors: JE
authors: Gomes
authors: José D A
authors: JD
authors: de Souza
authors: Daniel J
authors: DJ
authors: Rigden
authors: Hudson B
authors: HB
authors: Ramos
authors: Carlos R
authors: CR
authors: Soccol
authors: Maria F
authors: MF
authors: Grossi-de-Sa
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D032621:DNA Shuffling / Q000379:methods*; D004731:Endotoxins; D006460:Hemolysin Proteins; D007300:Insect Control / Q000379:methods*; D007814:Larva; D007928:Lethal Dose 50; D058977:Molecular Sequence Annotation; D008969:Molecular Sequence Data; D009154:Mutation; D019151:Peptide Library; D055550:Protein Stability; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D048889:Weevils
chemical_list: D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D004731:Endotoxins; D006460:Hemolysin Proteins; D019151:Peptide Library; C030956:insecticidal crystal protein, Bacillus Thuringiensis