A novel SPR based method for measuring diffusion coefficients: From small molecules to supramolecular aggregates

Investigating peptides and proteins conformations in vitro is of paramount importance in biochemistry and cell biology, as the understanding of many physiological pathways and pathological processes, which underscore the onset and progression of “conformational diseases”, is closely dependent on the actual possibility of monitoring the conformation, oligomerization and the specific properties, such as metal-binding features, that proteins adopt in complex systems. In this work, we report a newly designed Surface Plasmon Resonance (SPR) based dispersion analysis, hereby named D-SPR, which allows to measure the diffusion coefficients of molecules with unprecedented easiness and precision. Several small molecules have been tested with this new approach, and the diffusion coefficients obtained are in accordance with the values reported in the literature. A theoretical background is given and the newly designed method has been also applied to carnosine, a dipeptide which has recently attracted great attention by virtues of its anti-oxidative, anti-aggregating and enzyme activating properties. Results clearly show the high performance of the new method, which is based on the newly unveiled SPR capability to measure diffusion coefficients, to give information on carnosine metal-induced oligomerization, expanding the potentiality of commonly used SPR instruments well over the canonic investigation of biomolecular interactions.