Electron transport proteins

1. ELECTRON TRANFER PROTEINS
Babita Neupane | B.Sc.Ag | M.Sc.Bioinformatics |neupanebabita3@gmail.com
PROTEIN-PROTEIN INTERACTIONS

2. ELECTRON TRANSPORT CHAIN
➢ It is a series of protein complexes and molecules located in the inner mitochondrial
membrane of eukaryotic cells and the plasma membrane of prokaryotic cells.
➢ It is a critical component of aerobic cellular respiration, responsible for the final
stages of energy production.
The ETS consists of several protein complexes embedded within the inner
mitochondrial membrane.
Complex I (NADH dehydrogenase) contains Flavin mononucleotide (FMN), which
accepts 2 electrons and H + from 2 NADH to become the reduced form of FMNH2; also
contains iron atoms, which assist in the transfer of the e − and H + to coenzyme Q.
Complex II (Succinate dehydrogenase) contains iron and succinate, which oxidizes
FAD to form FADH23.
Coenzyme Q Accepts electrons from FMNH2 (complex I) and FADH2 (complex II) &
transfers electrons to complex III.
Complex III (cytochrome b) It contains heme group, in which the Fe 3+ accepts the
electrons from coenzyme Q to become Fe 2+ & transfers electrons to cytochrome c.
Cytochrome C It contains the heme group, in which the Fe 3+ accepts the electrons
from complex III to become Fe 2+ & transfers electrons to complex IV.
Complex IV (cytochrome A) It contains the heme group, in which the Fe 3+ accepts
electrons from cytochrome c to become Fe 2+ransfers electrons to O2, which is
combined with hydrogen to form H2O
Complex V (ATP synthase) It contains a proton channel that allows for protons to cross
into the matrix, using the proton gradient energy to form ATP.

4. INTRODUCTION
➢Electron transfer proteins facilitate the movement of electrons in biological systems.
➢They are involved in processes such as energy production, metabolism, redox reactions,
and signaling.
➢These proteins act as intermediaries in electron transport chains, transferring electrons
between donors and acceptors.
➢They enable the synthesis of ATP and play a crucial role in essential cellular functions.
➢Examples of electron transfer proteins include cytochromes, flavoproteins, and iron-sulfur
proteins.
➢These are highly regulated and coordinated within cells to ensure proper functioning and
maintain cellular homeostasis.
➢Dysfunction or mutations in electron transfer proteins can lead to various diseases,
including mitochondrial disorders and certain types of cancer.
➢Studying electron transfer proteins and their mechanisms is vital for understanding
fundamental biological processes and developing new therapeutic approaches.

5. Structure and Classification of Electron Transfer Protein
Based on Structure
i. Globular Proteins: These proteins have
a compact, folded structure with a
defined three-dimensional shape.
Examples include cytochromes and
ferredoxins.
ii. Membrane Proteins: These proteins are
embedded within cellular membranes
and often have specific structural
features to facilitate electron transfer
across the membrane. Examples
include cytochrome c oxidase and
photosynthetic reaction centers.
Ferredoxin Ferredoxin
Cytochrome C oxidase

6. Based on Cofactor composition
i. Heme Proteins: These proteins contain heme groups, which consist of a
porphyrin ring coordinated to an iron atom. Heme proteins include cytochromes
and catalases.
ii. Iron-Sulfur Proteins: These proteins contain iron-sulfur clusters as cofactors,
which consist of iron atoms coordinated to inorganic sulfur atoms. Examples
include ferredoxins and high potential iron-sulfur proteins (HiPIPs).
iii. Copper Proteins: These proteins contain copper ions as cofactors and participate
in electron transfer reactions. Examples include cytochrome c oxidase and
plastocyanin.
iv. Flavoproteins: These proteins contain flavin nucleotides (such as flavin adenine
dinucleotide - FAD or flavin mononucleotide - FMN) as cofactors.
Flavoproteins include flavodoxins and flavocytochromes.

7. Based on electron transfer mechanisms
i. One-Electron Transfer Proteins
These proteins transfer electrons one at a time, typically through a series of
redox reactions involving electron carriers such as heme groups or iron-sulfur
clusters.
ii. Multi-Electron Transfer Proteins
These proteins can transfer multiple electrons in a single step, often involving
cofactors such as flavins or copper ions.

8. SOME CRUCIAL ELECTRON TRANSFER PROTEINS

9. Cytochromes
➢ A group of electron transfer proteins that
contain heme prosthetic groups.
➢ They participate in electron transport
reactions and can be classified into
different classes, such as cytochrome c,
cytochrome b(complex II and III), and
cytochrome a (complex IV),
cytochrome and f and cytochrome P450.
➢ Cytochromes help establish a proton
gradient across membranes, which
drives ATP synthesis through
chemiosmosis.
➢ Cytochromes play a crucial role in
various redox reactions, including those
involved in the electron transport chain.

10. Iron-Sulfur Proteins
➢Iron-sulfur proteins contain iron-sulfur clusters as cofactors.
➢The clusters can have different structures, such as cubane-like, [2Fe-2S], [3Fe-4S], and [4Fe-4S].
➢They participate in electron transfer reactions, serving as electron carriers in metabolic pathways
and electron transport chains.
➢Iron-sulfur proteins are involved in enzyme catalysis, facilitating redox reactions, substrate
binding, and activation.
➢They can act as sensors for environmental signals, modulating gene expression or enzyme activity
in response to oxygen or redox status.
➢Iron-sulfur cluster biogenesis involves specific biosynthetic pathways for cluster assembly,
transfer, and insertion into target proteins.
➢Examples of iron-sulfur proteins include ferredoxins, aconitase, Rieske proteins, and nitrogenase.

11. Flavoproteins
➢Flavoproteins are a group of electron transfer proteins
that contain a prosthetic group called a flavin cofactor,
which is derived from riboflavin (vitamin B2).
➢The flavin cofactor can exist in two forms: flavin
mononucleotide (FMN) and flavin adenine dinucleotide
(FAD).
➢The flavin cofactor undergoes reversible changes in its
redox state, allowing it to accept or donate electrons
during enzymatic reactions.
➢These proteins participate in a wide range of electron
transfer reactions, including oxidation-reduction
reactions and electron transfer to oxygen.
➢Flavoproteins are found in many enzyme systems,
including the electron transport chain and various
oxidoreductases.

12. Copper Proteins
➢Copper proteins contain copper ions as their cofactors,
which participate in electron transfer reactions.
➢The two main copper proteins in the electron transport
chain are cytochrome c oxidase and
plastocyanin(plant)
➢These proteins contains copper centers, including a
binuclear copper site called the binuclear center
(BNC).
➢The binuclear center in cytochrome c oxidase acts as a
relay point, allowing for the stepwise transfer of
electrons during the reduction of oxygen.
➢The copper ions in these proteins can exist in different
oxidation states (Cu+ and Cu2+) and undergo
reversible redox reactions, allowing for the transfer of
electrons.

13. Quinones
• Quinones are not proteins themselves; they can interact with proteins in biological
systems.
• For example, in the electron transport chain, quinones such as ubiquinone
(Coenzyme Q) can associate with protein complexes and shuttle electrons between
different protein-bound redox centers.

14. Implications of study of electron transfer proteins in Bioinformatics
i. Protein structure prediction
ii. Functional annotation
iii. Protein-protein interactions
iv. Enzyme mechanism prediction
v. Evolutionary analysis
vi. Drug design and target identification
vii. Systems biology and network analysis
By leveraging the knowledge and properties of electron transfer proteins, bioinformatics approaches
can provide valuable insights into protein function, structure, interactions, evolution, and contribute to
various applications in drug discovery and systems biology.

15. THANK YOU !!