Are histidine rings the main potential sites of the interaction between proteins and the fluorescent Mg2+ indicator Mag-indo l?

Add time:07/15/2019    Source:sciencedirect.com

The investigation of the physicochemical properties of Mag-indo l, a fluorescent probe used for intracellular magnesium measurements, has shown that, in a biological environment, the deprotonated form of this probe is in simultaneous equilibrium with a protonated form, a protein and a magnesium-bound form.To understand the origin of the interaction of Mag-indo l with proteins, we have studied the effect of pH on the binding of Mag-indo l with bovine serum albumin (BSA). This interaction occurs for pH ⩽ 8.5. This indicates that interaction should take place with the protonated amino acids histidine, lysine and arginine.The investigation of the interaction of Mag-indo l with these amino acids, or the corresponding homologous polypeptides, has shown that interactions are only observed between Mag-indo l and histidine and Mag-indo l and polyhistidine. Furthermore, the interaction with histidine induces a blue shift of only 7 nm of the fluorescence spectrum of Mag-indo l, whereas the interaction with polyhistidine induces a blue shift of 28 nm of the fluorescence spectrum of Mag-indo l. The latter value, similar to that observed for the binding of Mag-indo l to BSA, indicates that binding occurs through an interaction mediated by the histidine ring.

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