************OWARI COMPLEX SEMINAR LXIV************

Title : Structural Insights into Membrane-Pore 
        Formation and Target Specificity of 
        Bacillus thuringiensis Mosquito-Specific 
        Toxins

Speaker : Assoc. Prof. Chanan Angsuthanasombat

Affiliation : Institute of Molecular Biosciences,
              Mahidol University, Thailand

Date : Tue. Oct. 21th, 13:00 pm (Almost one hour)

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 
betha-hairpin to serve as a lipid anchor required 
for an efficient membrane-insertion of the 
pore-lining alpha4-alpha5 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 betha10-
betha11 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 alpha4-alpha5 
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 alpha4 
and alpha5 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.

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