Structure of IgG Molecule

2. CONTENTS
 What are immunoglobulins?
 Physical characteristics of immunoglobulin
molecule
 Structure of immunoglobulin molecule
 Classes of immunoglobulins
 Chemical structure of Human IgG molecule
 IgG Subclasses
 Role of IgG in human immune response
 Multiple Myeloma

3.  The defense strategies of the body are
collectively referred to as immunity.
 Molecules which are responsible for immune
function of the body are termed as
immunoglobulin.
 Immunoglobulin , specialized group of
proteins mostly associated with gamma-
globulin of plasma protein.
 Immunoglobulins are glycoprotein molecules.
WHAT ARE
IMMUNOGLOBULINS?

4.  Immunoglobulin molecule consists of two heavy
chains and two light chains:
 Heavy chains(H) : Molecular Weight(53,000 to
75,000 each)
 Light chains(L) : Molecular Weight(23,000 each)
 AMINO ACIDS
 Heavy chains : 450 amino acids each
 Light chains : 212 amino acids each
PHYSICAL CHARACTERISTICS
F IMMUNOGLOBULIN MOLECUL

5.  Immunoglobulin is a Y-shaped tetramer.(H2L2).
 Heavy chains of immunoglobulin are linked with
carbohydrates so often called
GLYCOPROTEIN.
 Both heavy and light chains of immunoglobulin
has two regions(domains) :
 Constant
 Variable
 Specificity of immunoglobulin molecule is due to
variable regions in heavy and light chains.
TRUCTURE OF IMMUNOGLOBUL
MOLECULE

6.  The variable and constant regions differ with
respect to heavy and light chains.
 HEAVY CHAIN
 Constant: Three quarters of amino acid terminal
is constant(CH1 ,CH2 ,CH3 )
 Variable: One quarter of amino acid terminal is
variable(VH)
 LIGHT CHAIN
 Constant: Amino terminal half of light chain(CL)
 Variable: Carboxy terminal half of light chain(VL)
TRUCTURE OF IMMUNOGLOBUL
MOLECULE

8.  Humans have five classes of
immunoglobulins depending on the type of
heavy chain present in them.
 Five types of antibodies are
IgG,IgA,IgM,IgE,IgD-containing heavy chains
 Two types of light chains are present-namely
kappa and lambda.
CLASSES OF
IMMUNOGLOBULINS

9. TYPE H-CHAIN STRUCTU
RE
FUNCTION
IgG γ CHAIN Y-SHAPED
MONOMER
MOSTLY RESPONSILE
FOR HUMORAL
IMMUNITY
IgA α CHAIN MONOMER
OR DIMER
PROTECTS THE BODY
SURFACE
IgM µ CHAIN PENTAME
R
HUMORAL IMMUNITY
AND SERVES AS THE
FIRST LINE OF
DEFENSE
IgD δ CHAIN Y-SHAPED
MONOMER
B-CELL RECEPTOR
CLASSES OF Ig

10. TYPES OF
IMMUNOGLOBULINS

11. CHEMICAL STRUCTURE AND
FUNCTIONS OF HUMAN
IMMUNOGLOBULIN G(IgG)
MOLECULE

12. GRAMATIC REPRESENTATIO
OF HUMAN IgG

13.  IgG antibodies are large molecules of
about 150 kDa made of four polypeptide
chains.
 It contains two identical class Y heavy
chains of about 50 kDa and two
identical light chains of 25 kDa.
 Linkages present between the chains
are disulphide linkages.
STRUCTURE OF HUMAN IgG
MOLECULE

14.  There are four IgG subclasses described in
human, mouse and rat.
 They differ in the number of disulphide bonds
and the length and flexibility of the hinge
region.
 The four subclasses are as follows:
 IgG1 : Comprises 60-65% of main IgG
subclass and ,mainly responsible for thymus
mediated immune response against proteins
and polypeptide antigens.
IgG SUBCLASSES

15.  IgG2 : Comprises20-25% of the main
subclass and is prevalent immune response
against carbohydrate-/polysaccharide
antigens.
 IgG3 : Comprises around 5-10% of total IgG
and plays a major role in immune response
against protein or polypeptide antigens.
 IgG4 : Comprises usually less than 4% of
total IgG. It does not bind to polysaccharides
and precise role is mostly unknown.
IgG SUBCLASSES

16. SUBCLASSES OF HUMAN
IgG

17. Major immunoglobulin in blood, lymph
fluid, cerebrospinal fluid and peritoneal
fluid.
It is a key player in humoral immune
response.
Serum IgG in healthy humans presents
approximately 15% of total proteins
beside albumins, enzymes, and other
globulins and many more.
ROLE IN IMMUNE RESPONSE

18.  A plasma cell cancer constitutes 1%of all
cancers affecting the population.
 Occurs due to malignancy of a single clone of
plasma cells in bone marrow.
 This results in overproduction of abnormal
immunoglobulins mostly IgG and in some
cases IgG or IgM.
 Often leads to Amyloidosis i.e. deposits of light
chain fragments in tissues (liver, kidney ,
intestine.

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