Photosensitized Formation of Soluble Bionanoparticles of Lysozyme

Abstract

Photosensitized crosslinking of hen egg-white lysozyme (LZ) in buffer solutions was obtained by blue-LED excitation of ruthenium (II) tris-bipyridyl dication (Ru(bpy)32+) in a molar excess of persulfate anion (S2O82−), both in the absence and presence of dissolved oxygen. The results show a rapid monomer consumption of >75 %, with sequential formation of soluble LZ nanoparticles, e. g., dimers (LZ2),…n-mers (LZn≥6) with diameters from 6 to 13 nm, regardless of the presence of dissolved oxygen in solution. The bionanoparticles are crosslinked through 3,3'-dityrosine (diTyr) bonds, by the recombination of tyrosyl radicals of Y20, Y23, and Y53 residues of different protein molecules, produced by intermediated oxidants Ru(bpy)33+ and SO4.− generated after excitation. Furthermore, under aerobic conditions, photosensitized formation of singlet molecular oxygen (1O2) also results in the oxidative transformation of tryptophan residues into fluorescent kynurenine-type derivatives. These findings may contribute to the rational development of functional protein bionanoparticles.