Crystal Nucleation of Proteins Induced by Surface Plasmon Resonance

The crystallization of lysozyme and ribonucleaseA was induced using photochemical reactions triggered by surface plasmon resonance of gold nanostructures. The tryptophan residues of the protein are radicalized by the enhanced electric field induced by surface plasmon resonance. This radical reacts in the protein molecule to produce a reaction intermediate in which a nearby tyrosine residue is radicalized. This reaction intermediate reacts with another protein to form a dimer linked by tyrosine residues. Since this dimer is covalently bonded, it is stable without decomposition. With this as a nucleus, it grows into a crystal. An enhanced electric field induced by surface plasmon resonance of gold nanostructures was used to radicalize amino acids in proteins. Surface plasmon resonance induced by visible light radicalizes amino acids by the same mechanism as multiphoton absorption. When a metastable solution of lysozyme and ribonucleaseA was dropped on the substrate on which the gold nanostructure was constructed, and surface plasmon resonance of the gold nanostructure was induced, crystals precipitated.