engleski

Binding of indole-3-acetic acid derivatives to serum albumin

Auxins, in coordination with other plant hormones, regulate practically all aspects of plant growth and development. However, the mechanism of auxin action is still poorly understood. The main goal of this study was to explore the interactions of indole-3-acetic acid and its derivatives with human serum albumin as a model protein. It is known that serum albumins specifically bind indolic compounds and, in their amino acid sequences, share certain analogies with some auxin-binding proteins of plant origin. Correlation of the relative binding constants of indole-3-acetic acids to serum albumin with structural and physico-chemical descriptors reveals that affinities are dominantly influenced by hydrophobic interactions. As a rule, more lipophilic auxins bind more strongly than more polar analogues. Alkyl groups at indole ring position 2 obstruct proper orientation of the molecules within the binding site, while substituents at position 6, if more voluminous than fluorine, favor strong binding to the protein. Electron withdrawing substituents enhance the binding affinities of these compounds for the protein. Esterification of the carboxyl group as well as methylation of the indole-ring nitrogen does not lead to drastically reduced binding affinities. Comparison of the binding constants of indole-3-acetic acids to human serum albumin with their growth promoting activities in Avena coleoptiles indicates that the putative plant receptor is sterically more demanding.

ring-substituted indole-3-acetic acid; IAA; human serum albumin; HSA; substituent effect on ligand binding; structure-affinity relationship

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