Plastocyanin is a copper-containing protein involved in electron transfer during photosynthesis. It carries electrons from cytochrome f to photosystem I. The structure of plastocyanin has been characterized through X-ray crystallography, revealing a beta-barrel structure and trigonal copper binding site. Plastocyanin cycles between its reduced and oxidized states as it transfers electrons between cytochrome f and photosystem I via specific reaction pathways. As an essential component of photosynthesis, plastocyanin plays an important role in environmental processes.

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 b6f
complex from photosystem II and P700+ from photosystem I.
Cytochrome b6f 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.
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