The role of β18-β19 loop structure in insecticidal activity of Cry1Ac toxin from Bacillus thuringiensis

• 来源期刊: 科学通报(英文版)
• 年，卷（期）: 2008,（20）
• 页码范围: 3178-3184
• 页数: 7页
• 语种: 英文
• DOI: 10.1007/s11434-008-0391-5

摘要

The β18-β19 loop in domain Ⅲ of Cry1Ac toxin is unique among Bacillus thuringiensis Cry proteins. In this study, the role of the loop structure in insecticidal activity of Cry1Ac toxin was investigated. Alanine scanning mutations within the loop were initially generated and most mutants were over-expressed and reduced toxicity at different degrees, except mutant N546A that showed almost 2 times enhanced toxicity against Helicoverpa armigera larvae. Further mutagenic analysis of N546 re-vealed that a charged amino acid in this position would cause very unfavorable influence on insecti-cidal activity. In addition, the deletion of N546 led to protein instability because of destruction of the loop integrity. Besides, mutant W544F was much more toxic than W544Y, indicating that hydrophobic nature of the position was important for maintaining the stability and activity of Cry1Ac protein. These findings are the first biological evidence for a structural function of β18-β19 loop in insecticidal activity of the Cry1Ac toxin.