************第６４回尾張コンプレックスセミナー*************
　　　　
題  　目：　膜細孔形成への構造的洞察とバチルス－スリンギエ
　　　　　　ンシス蚊特異性毒素の標的特異性

Title   ：　Structural Insights into Membrane-Pore 
            Formation and Target Specificity of Bacillus 
            thuringiensis Mosquito-Specific Toxins

発 表 者：　Chanan Angsuthanasombat
Speaker ：　Assoc. Prof. Chanan Angsuthanasombat

所　  属　 ：  マヒドン大学分子生物科学研究所
Affiliation：  Institute of Molecular Biosciences, 
               Mahidol University, Thailand

日  　時：　 １０月２１日（火）午後１時００分～（約１時間）
Date    ：　 Tue. Oct. 21th, 13:00 pm (Almost one hour)

場　  所： 　情報科学研究科４階演習室
Place   ：   4F Seminar Room, Graduate School of 
             Information Science

Abstract：
We have been devoted to discovering a multitude of toxic 
mechanisms of bacterial protein toxins of interest, 
particularly the cytolytic pore-forming toxins, 
e.g. insecticidal δ-endotoxins (Cry4Aa & Cry4Ba) from 
Bacillus thuringiensis. A novel concept has been proposed 
for better explaining the toxicity involvement of 
Cry4Ba-helix 7 which could transform to a membrane-inserted 
β-hairpin to serve as a lipid anchor required for an 
efficient membrane-insertion of the pore-lining a4-a5 
hairpin [Arch Biochem Biophys-2009,482:17]. We employed 
MD simulations combined with PBSA calculations to prove 
that the pre-pore Cry4Aa trimer is stable in solution 
[PMC-Biophys-2010,3:1]. Our quantitative binding studies 
via QCM together with molecular docking provided first 
structural insights into toxin-receptor interactions 
between Cry4Ba and GPI-linked alkaline phosphatase 
[Appl Environ Microbiol-2011,77:6836]. We further 
demonstrated that Cry4Ba utilizes two critical aromatic 
loop-residues, Tyr332 and Phe364, for synergistic toxicity 
with its alternative receptor-Cyt2Aa2 [Biochem Biophys Res 
Commu-2013,435:216]. Recently, single-reversal charge in 
the β10-β11 receptor-binding loop, Cry4Aa-Lys514 or 
Cry4Ba-Asp454, was found to reflect their different 
toxicity against Culex mosquito-larvae [Biochem Biophys 
Res Commu-2014,450:948]. Moreover, the polarity of the 
Cry4Ba a4-a5 loop residue-Asn166 was demonstrated to be 
important for ion permeation and pore-opening [Biochem 
Biophys Acta-Biomemr-2014,435:216]. We also verified the 
functional significance of intrinsic stability toward the 
Pro-rich cluster in the exclusively long loop connecting 
α4 and α5 of Cry4Aa [Biochem Biophys Acta-Prot&Proteom-
2014,435:216]. Altogether, these understandings of their 
actual underlying toxic mechanisms would bolster the 
future development of better engineered biopesticides for 
control of such disease-carrying vectors.


***********************************************************