Structural stabilization displayed in the soluble phase of cocrystallization of flavianic acid with trypsin in acid media

Coprecipitation and cocrystallization of proteins with synthetic dyes are k nown to involve reversible denaturation processes which can offer specifici ty towards a target protein. Although the knowledge of conformational equil ibrium and how to control it are central into the basic molecular dynamics of protein precipitation, the exact molecular mechanism of the precipitatio n remains unknown. Aiming at understanding the events that take place befor e the coprecipitation step of generic dye-protein systems, we investigated the binding of flavianic acid to bovine trypsin, using approaches of visibl e and second-derivative ultraviolet spectroscopy, viscosimetry, densimetry and circular dichroism. The results suggest a restricted transconformation of the macromolecule linked to dye binding at a stoichiometry of 1:1. An in crease on the protein secondary structures occurred together with an electr o-constriction effect on trypsin, a borderline event to the coprecipitation process, suggesting a stabilized structure for trypsin as a ligand-induced molten globule-like state. (C) 2001 Societe francaise de biochimie et biol ogie moleculaire / Editions scientifiques et medicales Elsevier SAS. All ri ghts reserved.