Introduction Common terms used Protein ligand interaction 1)in oxygen binding protein Heme Structure of hemoglobin Ligand binding effected by protein structure Oxygenation &deoxygenation Cooperative binding of oxygen Models for cooperative binding Hb also transports H+&co2 2)complementary interaction immune system &immunoglobulin Introduction Structure of antibodies Binding of antigen to antibody Applications Conclusion Reference

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

2.  Introduction
 Common terms used
 Protein ligand interaction
 1)in oxygen binding protein
 Heme
 Structure of hemoglobin
 Ligand binding effected by protein structure
 Oxygenation &deoxygenation
 Cooperative binding of oxygen
 Models for cooperative binding
 Hb also transports H+&co2
 2)complementary interaction immune system &immunoglobulin
 Introduction
 Structure of antibodies
 Binding of antigen to antibody
 Applications
 Conclusion
 Reference

3.  Protein are the most abundant intercellular
macromolecules constitute about half the dry weight of
most organism .
 Protein are dynamic molecules whose function almost
Invariably depend on interaction with other molecules
On interaction with other molecules .

4. COMMON TERMS USED
• LIGAND- A molecule of any kind bound reversibly
to a protein is called a ligand .
• A ligand may be of any kind including protein .
• BINDING SITE –the site on a protein where a
ligand binds is called binding site .
• INDUCED FIT-the structural adaptation that
occurs between protein and ligand is called induced
fit.

5.  1)in oxygen binding protein –He reversible binding
of a ligand to the protein is well illustrated in two
oxygen binding protein .
 Myoglobin
 Hemoglobin
 Hemoglobin is the oxygen transporter in erythrocytes
and transports oxygen from the lungs ,gills or skin of
an animal to this capillary for use in respiration.
 Myoglobin stores and facilitates oxygen transport in
rapidly respiring muscles.

6.  HEME-
 oxygen is poorly soluble in aqueous solution and cannot be
carried to the tissues in sufficient quantities if it simply
dissolved in the blood serum.
 Multicellular organism exploit the property of metal
Especially iron and copper to carry oxygen that has high
tendency to bind oxygen.
In these organisms iron is incorporated in to a protein bound
prosthetic group is called heme.

8. STRUCTURE OF HEMOGLOBIN –
Hemoglobin is roughly spherical ,with a diameter
Of nearly 5.5nm.
It is a tetrameric protein containing four heme
prosthetic groups ,one associated with each
polypeptide chain .
Adult hemoglobin contains two types of globins
,two alpha chain and two bita chains .(146
residues) each.
The four polypeptide chain fit together almost
tetrahedrally to produce characteristic quaternary
structure.

10.  The interaction of ligand to protein is greatly effected by
protein structure is often accompanied by conformational
changes.
 The binding affinity of co to heme is 20,000 times better than
O2 but when heme is component of myoglobin it is reduced
to 100 times i.e. only 200 times better than O2.
 Oxygen binds to heme with the O2 axis at angle a binding
conformation readily accommodated by myoglobin .

12.  OXYGENATION AND DEOXYGENATION OF
HEMOGLOBIN- x ray analysis have reveled two
major conformation of Hb.
 R state- conformation of oxy Hb.
 T state- conformation of deoxy Hb

14.  Bonds involved in the structure of hemoglobin .
 The four chains are held together by non covalent
interactions.
 The alpha and beta chains are held together as a pair by
ionic and hydrogen bonds .
 The two pairs alpha1 beta 1 and alpha2 beta2 which act as
a dimers are then joined by additional ionic bonds
hydrogen bonds and hydrophobic forces.

15.  COOPERATIVE BINDING OF O2 WITH
HEMOGLOBINS- hemoglobin binds oxygen efficiently in
lungs where the po2is 13.3 kpa and release O2 in tissues where
the po2 is about 4kpa .myoglobin is ill-suited for this function .
 A protein with high affinity towards O2 would bind it
efficiently in lungs but would not release much of it in the
tissue.
 If the protein bound O2 with sufficiently low affinity to release
it in the tissue ,it would not pick up much oxygen in the lungs.
 Hemoglobin has properly of undergoing a transitional shift
from T to R state.
 T state is the low affinity state , R state is a high affinity state.

17.  HEMOGLOBIN –AN ALLOSTERIC PROTEIN –
 Allosteric means “allos”=other and “stereo”=solid or
shape.
 Ligands which induced different conformation to the
protein ,are known as modulators they can be of two
types .
 Homotropic-when ligand and modulator are identical ,the
interaction is homotropic .
 Hetrotropic- when modulator is ligand other than normal
ligand interaction is hetrotropic.

18. MODELS FOR COOPERATIVE BINDING.-
1)SEQUENTIAL MODEL- it is developed by Daniel E
Koshland Jr. in 1966 which in its simplest from make 3
ssumptions-
Only two conformational states ,T and R are associable to any
subunit .
 .

20.  Developed by Jeeques monad J. whyman and Jean
Pierre changeux in 1965.
 The essence of this model is that symmetry is conserved
in allosteric transition and that all subunits changes
confirmation together.

21. 

22.  HEMOGLOBIN ALSO TRANSPORTS AND CO2
 The co2 produced by oxidation of organic fuels in
mitochondria is hydrated to formed bi-carbonate.
 Co2 + H2O
H+ + HCO3

23.  Immune system provides to the human body
the infection particles .
 ANTTIBODY- antibodies are the effector
molecules of the hum oral immunity
produced by the B cells and reside in the
serum.
 ANTIGEN- Any molecules capable of
producing an immune response is called
antigen.

24. (

26.  Antibody is a Y shaped molecule having two heavy
chains and two light chains .
 DOMAINS-domains are the amino acid sequences that
are homologous in the two domain chains-Light
chain contain one variable vl and one constant
domain ,heavy chain contain one variable and four
constant cH1, cH2. cH3,Ch4.
 FAB FRAGMENT –the upper variable region that helps in
the binding of antigen I called the fab fragment.
 Fe fragment-the lower constant part help in biological
activity called fe fragment because it is found to
crystallize during cold storage.

27.  .HINGE REGION-the heavy chains contains an
extended peptide sequence between the cH1, and cH2
domains that has no homology with other domain this
region is called hinge region it is flexible and rich in
praline residues.

28.  Antibody bind tightly and specifically to the
antigen.
 The specificity of an antibody can be
determined by the amino acid residues in the
variable domains of its heavy and light chains
 Antigen-Ab interaction is quiet strong .
 Eg. Of this interaction between complex
derived from HIV and a fab molecule the
structural changes on the ag binding site are
quite striking.

29.  The protein ligand interaction has
application in the following methods:
 ELISA-enzyme linked immune sorbent assay.
 PRINCIPLE –it is based on principle that when
an enzyme is conjugated to an antibody and
reacts with a colorless substrate it generates
colored reaction product .
 The intensity of colored is measured and the
concentration of the antibody or the antigen
thus can be determined.

31. AFFINITY OF
CHROMATOGRAPHY-
The technique exploits the unique
property of extremely specific biological
Interaction of protein and protein ligand
interaction to achieve separation and
purification.
M + l k+l ML
Macromolecule ligand k-l complex.

33. •CONCLUSION-
 the proteins are a group of macromolecules that
has structural as well as regulatary function in the
body
Most of the function of protein is very much
influenced by its capacity to band with ligand.

34. REFERENCE
Principle of biochemistry –by nelson
and cox. 4th edition.
Biochemistry by-lubert streyer 5th edition
 www.wikipedia.com
 Date-12/3/2014
 Time-7 pm