Binding properties of Bacillus thuringiensis Cry4A toxin to the apical microvilli of larval midgut of Culex pipiens

• Published in: Bioscience, biotechnology, and biochemistry Vol. 65; no. 11; pp. 2419 - 2427
• Main Authors: Yamagiwa, M. (Okayama Univ. (Japan)), Kamauchi, S, Okegawa, T, Esaki, M, Otake, K, Amachi, T, Komano, T, Sakai, H
• Format: Journal Article
• Language: English
• Published: Tokyo Japan Society for Bioscience, Biotechnology, and Agrochemistry 01.11.2001; Japan Society for Bioscience Biotechnology and Agrochemistry
• Subjects: Animals; BACILLUS THURINGIENSIS; Bacterial Proteins - metabolism; Bacterial Toxins; Binding Sites; Biological and medical sciences; Biotechnology; Cry4A; Culex - metabolism; CULEX PIPIENS; Digestive System - metabolism; Endotoxins - metabolism; Epithelial Cells - metabolism; Fundamental and applied biological sciences. Psychology; Hemolysin Proteins; Hydrogen-Ion Concentration; In Vitro Techniques; INTESTINES; Larva - metabolism; LARVAE; membrane binding; Microvilli - metabolism; midgut; TOXINS
• ISSN: 0916-8451; 1347-6947
• DOI: 10.1271/bbb.65.2419

Cry4A is a dipteran-specific delta-endotoxin produced by Bacillus thuringiensis, and toxic to Culex pipiens (mosquito) larvae. The immunohistochemical staining of the midgut sections of C. pipiens larvae revealed that Cry4A bound in vitro and in vivo to the microvilli of the epithelial cells of posterior midgut and gastric caecae. The binding of digoxigenin-Iabeled Cry4A (DIG-Cry4A) to the apical microvilli was almost abolished in the presence of excess unlabeled Cry4A, suggesting that the binding of Cry4A to the microvilli was specific. Several Cry4A-specific binding proteins were detected using the ligand blotting technique with DIG-Cry4A. Moreover, an insertion assay was done, where the binding of DIG-Cry4A to the BBMVs was completely irreversible and did not compete with excess unlabeled Cry4A. On the basis of these results, we propose a schematic interpretation for the binding process of Cry4A.