Protein

Structure and Types

Objective: 

Illustration the nature structure 

Basil O M Saleh 

Immunoglobulins (Igs)

of Immunoglobulins, Types, AND Functions

Immunoglobulins:Structure and Function

• Definition:  Glycoprotein molecules that are 

immunogen and which function as antibodies

Immune serum

Ag adsorbed  serum

α

1

α

2

β

γ

+

-

albumin

globulins

Mobility

A

m

o

unt 

o

f 

pr

o

tei

n

produced by plasma cells (Specific Immune system )in response to an 

General Functions of 

Immunoglobulins

• Effector functions 

– Fixation of complement
– Binding to various cells

(Usually require Ag binding)

• Ag binding

– Can result in protection
– Valence

Basic Immunoglobulin Structure

• Immunoglobulins - heterogeneous

• Myeloma proteins - homogeneous 

immunoglobulins

Immunoglobulin Structure

• Heavy & Light 

Chains

• Disulfide bonds

– Inter-chain
– Intra-chain

C

H1

V

L

C

L

V

H

C

H2 

C

H3

Hinge Region

Carbohydrate

Disulfide bond

Immunoglobulin Structure

•

– V

L

& C

L

– V

H

& C

H

• Hinge Region

C

H1

V

L

C

L

V

H

C

H2 

C

H3

Hinge Region

Carbohydrate

Disulfide bond

Variable (V) & 

Constant (c) Regions

Immunoglobulin Structure

• Domains

– V

L

& C

L

– V

H

& C

H1

- C

H3

(or C

H4

)

• Oligosaccharides

C

H1

V

L

C

L

V

H

C

H2 

C

H3

Hinge Region

Carbohydrate

Disulfide bond

IgG molecule

Immunoglobulin Fragments: 

Structure/Function Relationships

• Fab

– Ag binding
– Valence = 1
– Specificity 

determined by V

H

and V

L

Papain

Fc

Fab

• Fc

– Effector functions

Immunoglobulin Fragments: 

Structure/Function Relationships

Ag  Binding

Complement Binding Site

Placental Transfer

Binding to Fc 

Receptors

Immunoglobulin Fragments: 

Structure/Function Relationships

• Fab

– Ag binding

• Fc

– Effector functions

• F(ab’)

2

Pepsin

Fc 
Peptides

F(ab’)

2

Human Immunoglobulin Classes

• IgG - Gamma (γ) heavy chains
• IgM - Mu (µ) heavy chains
• IgA - Alpha (α) heavy chains
• IgD - Delta (δ) heavy chains
• IgE - Epsilon (ε) heavy chains

Human Immunoglobulin

Light Chain Types

• Kappa (κ)
• Lambda (λ)

IgG

• Structure

– Monomer (7S)

IgG1, IgG2 and IgG4

IgG3

IgM

• Structure

– Pentamer (19S)
– Extra domain (C

H4

)

– J chain

Cµ4

J Chain

IgA

• Structure

– Serum - monomer
– Secretions (sIgA)

• Dimer (11S)
• J chain
• Secretory component

J Chain

Secretory Piece

IgD

• Structure

– Monomer
– Tail piece

Tail Piece

IgD

• Structure

• Properties

– 4th highest serum Ig
– B cell surface Ig
– Does not bind complement

IgE

• Structure

– Monomer
– Extra domain (C

H4

)

Cε4

In Summary

The Immunoglobulins are glycoprotein(CHO+Protein) in structure

and of different types IgG, M,A,D and E. All Igs are of two chain; heavy and light chain  

The light chain is of two types; Kappa and lymbda, the heavy chain are five types; 

of Heavy Chain(not Light Chain) defines the type of Immunoglobulin

The light chains and heavy chains are linked by sulfide bonds (S-S).

The MW of Igs is defined by the number of their amino acids and so by their 

poly peptide; the IgM has five poly peptides[PPs; (pentamer)], IgA has two PPs (dimer),

while other are monomer (one PP). The CHO is imprtant for protection of Igs from digestion

All Igs are synthesized by plasma cells of immune system and invloved in defence mechanism. 

The IgG is the immunoglobulin that pass the plecenta ?? tofetus and protect his or her during pregnancy.

gamma (IgG), alpha (IgA), delta (IgD), muo (IgM), and epsilon (IgE). The type of