TAILIEUCHUNG - Báo cáo khoa học: Vibrio cholerae hemolysin Implication of amphiphilicity and lipid-induced conformational change for its pore-forming activity

Vibrio choleraehemolysin (HlyA), a water-soluble protein with a native monomeric relative molecular mass of 65 000, forms transmembrane pentameric channels in target to lipid vesicles nonspecifically and without saturation; however, self-assembly is triggered specifically by we show that the HlyA partitioned quantitatively to amphiphilic media irrespective of their compositions, indicating that the toxin had an amphiphilic surface. | Eur. J. Biochem. 269 4351-4358 2002 FEBS 2002 doi Vibrio cholerae hemolysin Implication of amphiphilicity and lipid-induced conformational change for its pore-forming activity Kausik Chattopadhyay1 Debasish Bhattacharyya2 and Kalyan K. Banerjee1 1National Institute of Cholera and Enteric Diseases Kolkata 700 010 India 2Indian Institute of Chemical Biology Kolkata 700 032 India Vibrio cholerae hemolysin HlyA a water-soluble protein with a native monomeric relative molecular mass of 65 000 forms transmembrane pentameric channels in target biomembranes. The HlyA binds to iipid vesỉđes nonspecific-ally and without saturation however self-assembly is triggered specifically by cholesterol. Here we show ilial the HlyA partitioned quantitatively to amphiphilic media irrespective of their compositions indicating that the toxin had an amphiphilic surface. Asinloietinn. a p1-galactosyl-termin-ated glycoprotein which binds specifically to the HlyA in a lectin-glycoprotein type of interaction and inhibits carbohydrate-independent interaction of the toxin with lipid reduced effective amphiphilicity of the toxin significantly. Resistance of the HlyA to proteases together with the tryptophan fluorescence emission spectrum suggested a compact structure for the toxin. Fluorescence energy 1rans I er from Ihe HlyA to dansyl-phosphatidylethanolamine required the presence of cholesterol in the lipid bilayer and was synchronous with oligomerization. Phoepholipid bihiyer without cholesterol caused a partial unfolding of the HlyA monomer as indicated by the transfer of tryptophan residues from the nonpolar core of the protein to a more polar region. These observations suggested a partitioning of the HlyA to lipid vesicles is driven by the tendency of the amphiphilic toxin to reduce energetically unfavorable contacts with water and is not affected significantly by the composition of the vesicles and b partial unfolding of the HlyA at the lipid-water .

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