Tyrosinase-catalyzed site-specific immobilization of engineered C-phycocyanin to surface.

Enzymatic crosslinking of proteins is often limited by the steric availability of the target residues, as of tyrosyl side chains in the case of tyrosinase. Carrying an N-terminal peptide-tag containing two tyrosine residues, the fluorescent protein C-phycocyanin HisCPC from Synechocystis sp. PCC6803 was crosslinked to fluorescent high-molecular weight forms with tyrosinase. Crosslinking with tyrosinase in the presence of L-tyrosine produced non fluorescent high-molecular weight products. Incubated in the presence of tyrosinase, HisCPC could also be immobilized to amino-modified polystyrene beads thus conferring a blue fluorescence. Crosslinking and immobilization were site-specific as both processes required the presence of the N-terminal peptide in HisCPC.