Proteins folding and denaturation

3. Definition;
• PROTEIN–PROTEIN INTERACTIONS (PPIs) are
physical contacts of high specificity established between
two or more protein molecules to carry out their
biological functions effectively as result of these
interactions that include electrostatic forces, hydrogen
bonding and the hydrophobic effect.

4. Introduction;
Protein–protein interactions occur when two or more proteins bind together, often to
carry out their biological function.
The protein –protein interaction have commonly been termed the ‘INTERACTOME’
by scientists.
 French researchers first coined the term "interactome" in 1999; the first protein-protein
interactome data appeared in 2000.
WHY WE STUDY PPI?
Protein-protein interactions determine outcome of most cellular processes.
Proteins which are close homologues often interact in the same way

5. •Protein-protein interactions provide evolutionary history of protein sequence and
structural divergence
• PPIs are Pre-cursor to networks.
•Finding interactions between proteins involved in common cellular functions is a
way to get a broader view of how they work cooperatively in a cell.
•Experimental studies indicate that many diseases that are related to molecular
events occur due to lack of protein-protein interactions.
•Studying protein interactions, especially disease-related, beneficial for the process
of drug design.

6. Protein b
unknown
Protein a
known
Interaction
Better understanding of protein b’s function

7. Protein b
Function b
Protein a
Function a
Interaction
Detecting relationship between
pathways
Detecting new pathways

8. Examples of PPIs
Electron Transfer Protéines
Signal Transduction
Membrane Transport
CellMétabolism
Muscle Contraction

9. Signal Transduction

10. Importance of PPIs
Important field in cell biology & biochemistry.
Posttranslational modifications.
 Signaling networks.
 Important field in viral replication which is very difficult to predict.
Crucial for the understanding of the biological pathways, like cell
signaling .
PPI dysfunctions may lead to disease situations.
 Important targets for therapy and drug designing.

11. PPIs Classification
• Based on Affinity
Obligate
Non-obligate
• On The Basis of StabilityDuration of interaction
Permanent
Transient
• On The Basis Of Composition
Homo- Oligomers
Hetero-oligomers
• On The Basis Of Bonding
Covalent
Non-covalent

18. Role Of Water in PPIs
Water molecules play a significant role in the interactions between proteins.
The crystal structures of complexes, obtained at high resolution from different but
homologous proteins, have shown that some interface water molecules are conserved
between homologous complexes.
The majority of the interface water molecules make hydrogen bonds with both
partners of each complex.
Some interface amino acid residues or atomic groups of one protein partner engage
in both direct and water mediated interactions with the other protein partner.

19. Indirect interactions, mediated by
two water molecules, are more
numerous in the homologous
complexes of low affinity.
Thus, water molecules may facilitate
the interactions .

21. Yeast Two Hybrid System
•Also known as Y2H or two-hybrid screening.
• Molecular biology technique used to discover
protein-protein interactions and protein–DNA
interactions .
• Testing for physical interactions (such as binding)
between two proteins or a single protein and a
DNA molecule, respectively.
•Pioneered by Stanley Fields and Ok-kyu Song in
1989.

24. Yeast two hybrid system
Simple transcription
Reporter Gene
Transcription
DBD
DBD = DNA Binding Domain
AD
AD = Activation Domain
Upstream Activating Sequence
UAS

25. Yeast two hybrid system
Hybrid proteins
DBD
Bait
AD
fish

26. Reporter gene
transcription
UAS
DBD
BAIT
AD
FISH
Yeast two hybrid system
Hybrid proteins

27. Yeast two hybrid system
plasmids Plasmid A
DBD
Plasmid B
AD
Yeast

33. Applications Of PPIS
•Many PPIs are being used as therapeutic targets as they exhibit properties such as
allosteric sites.
•Maraviroc, a drug that inhibits CCR5 gp 120 interaction and is a prominent anti HIV
drug.
• Recently , a group of scientists were able to develop 30 peptides using protein–protein
interaction studies to inhibit telomerase recruitment towards telomeres.
•PPIs have been used to identify the functions of unknown proteins.
• It is based on the assumption that uncharacterized proteins have similar functions as
their interacting proteins

34. Factors
Affecting PPIs
Protein concentration, which in turn are affected by expression levels and
degradation rates.
 Protein affinity for proteins or other binding ligands.
Ligands concentrations (substrates, ions, etc.).
 Presence of other proteins, nucleic acids, and ions.
 Electric fields around proteins.
 Occurrence of covalent modifications.

35. THANK
YOU
Any
Queries?