Binding of azurin to cytochrome c 551 as investigated by surface plasmon resonance and fluorescence.

ABSTRACT

The interaction between azurin (Az) and cytochrome c 551 (CytC551) from Pseudomonas aeruginosa deserves particular interest for both its physiological aspects and their possible applications in bionano devices. Here, the kinetics of the interaction has been studied by surface plasmon resonance and fluorescence quenching. Surface plasmon resonance data have been successfully interpreted by the heterogeneous ligand model, which predicts the existence of two binding sites on the immobilized Az for CytC551 molecules in solution. On the other hand, the fluorescence study indicates the formation of a complex, with the involvement of the lone Az tryptophan (Trp) at position 48. The two different techniques point out the occurrence of an encounter complex between Az and CytC551 that evolves toward the formation of a more stable complex characterized by an equilibrium dissociation constant KD typical of transient interactions.