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Title: Aedes aegypti membrane-bound alkaline phosphatase expressed in Escherichia coli retains high-affinity binding for Bacillus thuringiensis Cry4Ba toxin
Authors: Anon Thammasittirong
Manasave Dechklar
Somphob Leetachewa
Kusol Pootanakit
Chanan Angsuthanasombat
Mahidol University
Kasetsart University
Keywords: Agricultural and Biological Sciences;Biochemistry, Genetics and Molecular Biology;Environmental Science;Immunology and Microbiology
Issue Date: 1-Oct-2011
Citation: Applied and Environmental Microbiology. Vol.77, No.19 (2011), 6836-6840
Abstract: Glycosylphosphatidylinositol-linked alkaline phosphatase (GPI-ALP) from the epithelial membrane of the larval midgut of Aedes aegypti was previously identified as a functional receptor of the Bacillus thuringiensis Cry4Ba toxin. Here, heterologous expression in Escherichia coli of the cloned ALP, lacking the secretion signal and GPI attachment sequences, and assessment of its binding characteristics were further investigated. The 54-kDa His tag-fused ALP overexpressed as an inclusion body was soluble when phosphate buffer (pH 7.5) was supplemented with 8 M urea. After renaturation in a nickel-nitrilotriacetic acid (Ni-NTA) affinity column, the refolded ALP protein was able to retain its phosphatase activity. This refolded ALP also showed binding to the 65-kDa activated Cry4Ba toxin under nondenaturing (dot blot) conditions. Quantitative binding analysis using a quartz crystal microbalance revealed that the purified ALP immobilized on a gold electrode was bound by the Cry4Ba toxin in a stoichiometry of approximately 1:2 and with high affinity (dissociation constant [K d ] of ~14 nM) which is comparable to that calculated from kinetic parameters (dissociation rate constant [k off ]/binding constant [k on ]). Altogether, the data presented here of the E. coli-expressed ALP from A. aegypti retaining high-affinity toxin binding support our notion that glycosylation of this receptor is not required for binding to its counterpart toxin, Cry4Ba. © 2011, American Society for Microbiology.
ISSN: 10985336
Appears in Collections:Scopus 2011-2015

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