Calcium-regulated interactions of human alpha-lactalbumin with bee venom melittin |
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Authors: | E A Permyakov V M Grishchenko L P Kalinichenko N Y Orlov K Kuwajima S Sugai |
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Institution: | Institute of Biological Physics, U.S.S.R. Academy of Sciences, Pushchino, Moscow Region. |
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Abstract: | Affinity chromatography, fluorescence and circular dichroism spectroscopy methods have been used to study the interaction of melittin, a 26-residue peptide from bee venom, with Ca2(+)-binding alpha-lactalbumin from human milk. It has been revealed that melittin binds to the apo- and acidic states of alpha-lactalbumin while the presence of Ca2+ makes the interaction essentially weaker. The association constant for the complex of melittin with apo-alpha-lactalbumin determined from spectropolarimetric melittin-titration data is 2 X 10(7) M-1. The complexation of alpha-lactalbumin with melittin decreases its affinity to Ca2+ by three orders of magnitude. The interaction of apo-alpha-lactalbumin with melittin causes some changes in the environment of its aromatic amino acid residues and drastically alters the conformation of melittin, increasing its alpha-helical content but leaving its single tryptophan residue accessible to water. In the case of the acidic state of alpha-lactalbumin the interaction does not induce an increase in alpha-helical content of melittin. |
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