Mag-indo-1-protein interaction as a tool for probing the 3D conformation of protein sub-domains: Influence of the chemical microenvironment of the histidin residue(s) on the parameters of the interaction

Magnesium complexation with Mag-indo-1 results in a shift of the emission fluorescence spectrum from 480 nm to 417 nm. Mag-indo-1 is also able to bind calcium and zinc. These cationic interactions induce the same spectral shift but the fluorescence intensity and the dissociation constant are dependent of the nature of the cation. Furthermore Mag-indo-1 bind also proteins through a specific interaction with some histidin residues. That interaction induces a characteristic spectral shift of the emission fluorescence spectra from 480 to 457 nM. Emission and synchronous fluorescence techniques have been used to monitor that interaction with proteins such as turkey and hen white egg lysozymes. Using a method of resolution of complex fluorescence spectra, it has been possible to calculate the number of interaction sites and the correlative dissociation constants. Depending on the nature of the protein a quenching of the natural fluorescence of the protein was observed, associated with an energy transfer from some tryptophan(s) to Mag-indo-1. Moreover the value of the dissociation constant was found dependent of the molecular microenvironment of the histidin residue. These results suggest that Mag-indo-1 could be used as an intramolecular fluorescent ruler to explore the changes in 3D conformation resulting from genetically induced amino-acid substitutions and to monitor changes in the chemical microenvironment of specific sub-domains of these proteins.

Duke Scholars

Author Tuan Vo-Dinh Biomedical Engineering