plastocyanin

it is a protein

1. EAST WEST UNIVERSITY Department of Genetic Engineering and Biotechnology   Course Title: Chemistry for Biologists-I Course Code: CHE108 Course Instructor: ABID AL REZA (Lecturer ) Group Name: “404 ERROR” Group Member: 1.Asma Hossain ; (2015-2-77-004) 2.Suraya Akter ; (2015-2-77-011) 3.Sabrina Akter Zarin ; (2015-2-77-041) 4.Tania Islam; (2016-1-77-036)

2. “ Plastocyanin ” Points : 1.Introduction 2. Structure 3. Function 4. Reaction 5.Conclusion

3. INTRODUCTION

4. Plastocyanin is a copper-containing protein involved in electron-transfer. The protein is monomer, with a molecular weight around 10,000 Daltons, and 99 amino acids in most vascular plants. It is a member of the plastocyanin family of copper-binding proteins. It carries electrons at one point in the electron transport chain.in its reduced form, it gives electrons directly to the systems that reduce nitrate and sulfate and via NADPH to the system that reduces carbon dioxide. Plastocyanin molecules are water soluble and can move through the inner space of the thylakoids .

5. Figure of Plastocyanin

6. STRUCTURE

7. Plastocyanin was the first of the blue copper proteins to be characterised by X-ray crystallography . The tertiary structure is a beta-barrel — common in proteins which bind to other proteins . The geometry of the copper bindingsite is described as a ‘distorted trigonal pyramidal’.The trigonal plane of the pyramidal base is composed of two nitrogen atoms (N1 & N2) from separate histidine residues and a sulfur atom (S1) from a cysteine residue. A second sulfur atom (S2) from an axial methionine residue froms the apex. The distortion occuers in the bond lengths between the copper atom and sulfur ligands.The Cu-S1 contact is much shorter (207 picometers ) than Cu-S2 (282 picometers ). The elongated Cu-S2 bonding destabilises the Cu II form and increases the redox potential or the protein.

8. In plant plastocyanins , acidic residues are located on either side of the highly conserved tyrosine -83. Algal plastocyanins , and those from vascular plants in the family Apiaceae , contain similar acidic residues but are shaped differently from those of plant plastocyanins —they lack residues 57 and 58. In cyanobacteria , the distribution of charged residues on the surface is different from eukaryotic plastocyanins and variations among different bacterial species is large. Many cyanobacterial plastocyanins have 107 amino acids. Although the acidic patches are not conserved in bacteria the hydrophobic patch is always present. These hydrophobic and acidic patches are believed to be the recognition/binding sites for the other proteins involved in electron transfer.

9. Fig : Structure of plastocyanin

10. FUNCTION

11. The aim of this review is to analyze the current state of knowledge concerning the blue copper protein plastocyanin (PC) focusing on its interactions with its reaction partners cytochrome f and P700. In photosynthesis,plastocyanin functions as an electron transfer agent between cytochrome f of the cytochrome   b 6 f complex from photosystem II and P700+ from photosystem I . Cytochrome   b 6 f   complex and P700 +  are both membrane-bound proteins with exposed residues on the lumen-side of the  thylakoid  membrane of  chloroplasts . Cytochrome f acts as an electron donor while P700+ accepts electrons from reduced plastocyanin .

12. Fig: Function of plastocyanin

13. REACTION

14. Plastocyanin (Cu2+Pc) is reduced (an electron is added) by cytochrome f according to the following reaction: Cu2+Pc + e− → Cu+Pc After dissociation, Cu+Pc diffuses through the lumen space until recognition/binding occurs with P700+, at which point P700+ oxidizes Cu+Pc according to the following reaction: Cu+Pc → Cu2+Pc + e− The redox potential is about 370 mV and the isoelectric pH is about 4.

15. In the reduced form of plastocyanin , His-87 will become protonated with a pKa of 4.4. Protonation prevents it acting as a ligand and the copper site geometry becomes trigonal planar. While the molecular surface of the protein near the copper binding site varies slightly, all plastocyanins have a hydrophobic surface surrounding the exposed histidine of the copper binding site.

16. CONCLUSION

17. In photosynthesis, plastocyanin functions are really important. Without photosynthesis we can’t imagine the significant living organisms of the environment . In a word, plastocyanin is an important metalloprotein for the environment. THANK YOU