| วัตถุประสงค์
: |
The objective of this project is to characterize the structure and function of the Bin toxin from Lysinibacillus sphaericus, which has been used, together with another well-known larvicide Bacillus thuringiensis subsp. israelensis, to control mosquito larvae, in many regions of the world. Over the past decade, collective findings have been produced from our laboratory, however, some critical information is still missing especially the structural information of individual Bin toxin subunits and their complex either in solution or in the membrane-mimicking environment. To work towards this goal, we have successfully solved, by X-ray crystallography, the structure of the BinB receptor-binding subunit of the binary toxin to high resolution of 1.75 ?. However, the full function of the binary toxin requires both BinA and BinB subunits, hence, the structural characterization of the BinA and the BinA/BinB complex remains to be accomplished. Also, solving the structure of the binary toxin in solution may not be enough to fully understand the molecular transitions that occur during the oligomerization and membrane insertion. Hence, the structures of the binary toxin subunits in the presence of membrane-mimicking environment such as detergent micelles remain to be elucidated. Together with the structural analysis, functional assays have been carried out in search of the critical regions and amino acids for the toxicity and specificity of the Bin toxin. Based on the close similarity of BinB structure and that of parasporin-2, one of the Bt toxins, which exhibits cytocidal activity to certain human cancer cells, it is thus of particular interest to explore the possible anti-tumor activity of Bin toxin. Our findings are expected to provide a structural framework to engineer the toxin for toxic enhancement, expand the host-range specificity, prevention of mosquito resistance as well as a potential medicinal application of Bin toxin as chemotherapeutic agent. This research project is a logical continuation of our ongoing studies on the structure and function of the binary toxin and will target four main objectives:
1. To understand the detailed structures, both in the solution and in the membrane-mimicking environment, of the Bin toxin components and their complex.
2. To identify the determinants for Bin toxin, guided by the structural results above, during the key steps of the toxicity including membrane interaction, receptor recognition and pore formation.
3. To elucidate the mechanism underlying the larval intoxication through the investigation of the intracellular trafficking and the larval midgut response mechanism.
4. To explore the possible anti-tumor activity of Bin toxin against human cancer cells for its potential medicinal application.
|
