The document discusses protein-ligand and protein-protein interactions, highlighting their essential roles in biological functions and molecular processes like DNA replication. It explains oxygen binding in hemoglobin and myoglobin, detailing their structural characteristics and cooperative binding mechanisms. Additionally, it covers the structure of immunoglobulin G in antigen interaction and the mechanics of muscle contraction involving actin and myosin.

1. PROTEIN LIGAND INTERACTION
&
PROTEIN PROTEIN INTERACTION
By
KAUSHAL KUMAR SAHU
Assistant Professor (Ad Hoc)
Department of Biotechnology
Govt. Digvijay Autonomous P. G. College
Raj-Nandgaon ( C. G. )

2. CONTENT
 INTRODUCTION
 Protein – ligand Intraction
Oxygen binding
Ag – Ab Intraction
 Protein – Protein Intraction
Muscle Contraction
• CONCLUSION
• Reference

3. INTRODUCTION
 Protein–protein interactions occur when two or more protein bind together,
often to carry out their biological function.
 Many of the most important molecular processes in the cell such as DNA
replication are carried out by large molecular machines that are built from a large
number of protein components organised by their protein–protein interactions.
 Interactions between proteins are important for the majority of biological
functions.
 For example, signals from the exterior of a cell are mediated to the inside
of that cell by protein– protein interactions of the signaling molecules.
 Indeed, protein–protein interactions are at the core of the entire interatomic
system of any living cell.

5. OXYGEN BINDING
 Heme consists of a complex organic ring structure,
protoporphynrin, to which is bound a single iron atom in
its ferrous (Fe2+ ) state.
 The iron atom has six coordination bonds, four to nitrogen
atoms that are part of the flat porphyrin ring system and
two perpendicular to the porphyrin state.
 Iron in the Fe 2+ state binds oxygen reversibly; in the Fe 3+
state it does not bind oxygen.

7. Protein structure affects how ligands bind
1. Steric effects
2. Molecular motions/breathing
in the structure
1: 20,000 1: 200

8. The structure of myoglobulin
*a single binding site for O2
*78% a helices
*His93 or HisF8 (the 8th
residue in a helix F) binds
to heme
*Bends between a helices

9. Fig. Comparison between Mb and Hbb

10. Fig. Dominant interactions between Hb subunits
>30 aa
19 aa (hydrophobic, H-bonds,
affected strongly upon O2 binding)

11. Hb undergoes a structural change on binding oxygen
Fig. The T(tense) R(relaxed) transition

12. Fig. Changes in conformation near heme on O2 binding

13. Hb binds oxygen cooperatively
Fig. A sigmoid (cooperative) binding curve
4 vs. 13.3 kPa
Mb – a single
subunit protein
Hb – 4 subunits,
an allosteric protein

14. Two models suggest mechanisms for cooperative binding
Concerted (all-or-none), 1965 Sequential, 1966

15. Fig. 7-17
Binding of BPG to deoxyHb
T state
T
R
O2
++
BPG is negatively charged

16. The structure of immunoglobulin G (IgG)

17. Binding of IgG to an antigen

18. The Ab-Ag interaction is the basis for a variety of
important analytical procedures
Ployclonal vs. monoclonal Ab
ELISA (enzyme-linked immunosorbent assay)

20. Protein interactions modulated by chemical energy
Actin, myosin, and molecular motors
Fig. Myosin

21. The major components of muscle
myosine
actine

22. Structure of skeletal muscle
relaxed
contracted

23. Muscle contraction

24. Molecular mechanism of muscle contraction
3~4 pN of forces, 5~10 nm movement/cycle

25. REFERANCE
LEHNINGER PRINCIPLES OF
BIOCHEMISTRY
FIFTH EDITION