Rusticyanin Explained

Rusticyanin (RCN) is a copper protein with a type I copper center that plays an integral role in electron transfer.^{[1] [2]} It can be extracted from the periplasm of the gram-negative bacterium Thiobacillus ferrooxidans (T. ferrooxidans), also known as Acidithiobacillus ferrooxidans (At. ferrooxidans).^[3] Rusticyanin is also found in the membrane-bound form in the surface of T. ferrooxidans. It is a part of an electron transfer chain for Fe(II) oxidation.^[4]

Function

As A. ferrooxidans can grow aerobically at pH values of 1.6 to 3.5, it obtains its energy for chemolithotrophic growth on soluble ferrous ions. Rusticyanin is involved in the respiratory oxidation of ferrous ions to ferric ions, producing three protons for every ferrous ion oxidized. The mechanism of electron transfer in the respiratory oxidation pathway of Fe²⁺ in A. ferrooxidans is still unclear despite decades of research in this area. However, the involvement of rusticyanin in shuttling electrons from a cytochrome c2 to another cytochrome c4 during the oxidation of ferrous to ferric ions is experimentally shown. Rusticyanin is thought to shuttle electrons from high molecular weight cytochrome via cytochrome c552 to cytochrome oxidase.^[5] Predicted functional partners include coxD (cytochrome c oxidase, aa3-type, subunit IV, 64 amino acids), coxC (cytochrome c oxidase, aa3-type, subunit III, 184 amino acids), ctaB (protoheme IX farnesyltransferase), Cyc2 (cytochrome c, 485 amino acids), AFE_3142 (major facilitator family transporter, 397 amino acids), coxA (cytochrome c oxidase, aa3-type, subunit I, 627 amino acids), Cyc1 (cytochrome c552, 230 amino acids), and AFE_3141 (rrf2 family protein, 146 amino acids).^[6]

Reactions

Fe(II) redox of cytochrome c552 and rusticyanin occurs with the following:^[7]

Fe²⁺_[membrane] + an oxidized rusticyanin_[membrane] → Fe³⁺_[membrane] + a reduced rusticyanin_[membrane];

a reduced rusticyanin_[membrane] + an oxidized cytochrome c552_[membrane] → an oxidized rusticyanin_[membrane] + a reduced cytochrome c552_[membrane];

a reduced rusticyanin_{[outside cell]} + an oxidized CycA1 cytochrome_{[outside cell]} → a reduced CycA1 cytochrome_{[outside cell]} + an oxidized rusticyanin_{[outside cell]}

Notes and References

1. Ronk. M.. Shively. J. E.. Shute. E. A.. Blake. R. C.. 1991-10-01. Amino acid sequence of the blue copper protein rusticyanin from Thiobacillus ferrooxidans. Biochemistry. 30. 39. 9435–9442. 0006-2960. 1892844. 10.1021/bi00103a007.
2. Walter. R. L.. Ealick. S. E.. Friedman. A. M.. Blake. R. C.. Proctor. P.. Shoham. M.. 1996-11-15. Multiple wavelength anomalous diffraction (MAD) crystal structure of rusticyanin: a highly oxidizing cupredoxin with extreme acid stability. Journal of Molecular Biology. 263. 5. 730–751. 0022-2836. 8947572. 10.1006/jmbi.1996.0612. free.
3. Yamada. Tohru. September 2004. Rusticyanin, a Bacterial Electron Transport Protein, Cause G1 Arrest in J774 and Apoptosis in Human Cancer Cells. Cell Cycle. 3. 1182–1187. 10.4161/cc.3.9.1125 . free.
4. Book: Shoham, Menachem. Handbook of Metalloproteins. John Wiley & Sons, Ltd.. 2006.
5. Hazra. T.K.. February 1992. Role of rusticyanin in the electron transport process in Thiobacillus ferrooxidans. Indian Journal of Biochemistry & Biophysics. 29. 77–81.
6. Web site: rus - Rusticyanin precursor - Acidithiobacillus ferrooxidans (strain ATCC 23270 / DSM 14882 / CIP 104768 / NCIMB 8455) - rus gene & protein. www.uniprot.org. en. 2018-05-26.
7. Web site: Mycobacterium colombiense an oxidized rusticyanin. biocyc.org. 2018-05-26.