Quantitative detection of conformational transitions in a calcium sensor protein by surface plasmon resonance

We determined the conditions under which surface plasmon resonance can be used to monitor at real-time the Ca(2+)-induced conformational transitions of the sensor protein recoverin immobilized over a sensor chip. The equilibrium and the kinetics of conformational transitions were detected and quantified over a physiological range of Ca(2+) and protein concentrations similar to those found within cells. Structural analysis suggests that the detection principle reflects changes in the hydrodynamic properties of the protein and is not due to a mass effect. The phenomenon appears to be related to changes in the refractive index at the metal/dielectric interface.