Azurin

Azurin is a small (~14 kDa) blue copper-containing electron transfer protein found in the periplasm of gram-negative bacteria, particularly *Pseudomonas aeruginosa*. Structurally, it is a monomer with a beta-barrel configuration stabilized by a copper ion coordinated by conserved amino acids[1][2][6][8]. Its classic biological role is to moderate single-electron transfer by cycling between Cu(I) and Cu(II) oxidation states during cellular respiration. Beyond its electron transfer function, azurin exhibits preferential cytotoxicity toward a variety of human cancer cells by entering these cells, binding to the tumor suppressor protein p53, and promoting apoptosis, while sparing most normal cells[3]. The internal p28 domain of azurin enables cell penetration and is being investigated as an anticancer peptide. Additional studies revealed that azurin can interfere with ephrinB2-mediated signaling in cancer cells, further supporting its potential as an antitumor agent. While not a receptor, enzyme, or transporter in the conventional sense, azurin’s distinctive redox properties and selective tumor-targeting functions position it as a novel protein therapeutic candidate and biological tool for studying electron transfer and cancer biology[3][1][8]. No currently approved drugs directly target azurin, but derivative peptides are undergoing research for cancer therapy.

Other names

Blue copper proteinCupredoxinPaz (for mature Pseudomonas aeruginosa azurin)Bacterial azurin

Induces apoptosis in cancer cells (via interaction with p53 and cytochrome c), Interferes with cell signaling (by mimicking ephrinB2 ligand and inhibiting EphB2 receptor signaling), Electron transfer via copper redox cycle