Azurin

Azurin is a small, monomeric, single-copper-containing metalloprotein belonging to the cupredoxin family. It is found in certain species of bacteria, particularly Pseudomonas aeruginosa and Alcaligenes denitrificans. Azurin functions as an electron transfer protein in the bacterial respiratory chain, shuttling electrons between cytochrome c oxidase and a reductase.

The protein's structure is characterized by a beta-barrel fold with the copper ion coordinated by residues including histidine, cysteine, and methionine. This unique coordination geometry gives azurin its intense blue color, which is characteristic of copper proteins with type 1 copper centers. The copper ion alternates between the Cu(I) and Cu(II) oxidation states during electron transfer.

Azurin has been the subject of extensive research due to its well-defined structure, relatively small size, and the intriguing properties of its copper center. Studies have focused on understanding the mechanism of electron transfer, the role of the protein environment in modulating the redox potential of the copper ion, and the potential applications of azurin in fields such as biosensors and nanotechnology. Furthermore, some research has explored the ability of azurin, or its derived peptides, to inhibit the growth of certain cancer cells.