Structure and function of individual parts of immunoglobulins. Classes of immunoglobulins, properties and functions. Monoclonal antibodies - preparation, use.

Immunoglobulins are class of proteins produced by B cells and plasma cells. Another term used to refer to Immunoglobulins are antibodies. They serve as line of defense by binding to antigens that correspond to the pathogens that invade our body.

Structure and function of Immunoglobulins

Basic structure :

Antibodies are Y shaped glycoproteins consisting of two small polypeptide chains and two large polypeptide chains. In each respective pair, the polypeptide chains are identical. There are five major classes of immunoglobulins, of which the most abundant in human sera are gamma globulins.

Each short arms of the Y shaped glycoprotein are composed of a pair of chains; light chain and heavy chain held together by disulfide bonds. The two arms are held together by one or more disulfide bonds by the hinge. The chains in immunoglobulins have similar tertiary structure with certain features, most notably "Immunoglobulin folds". Immunoglobulin folds are characterized "beta barrel" antiparallel beta pleated sheets connected by loops of variable and which are held together disulfide bond/s.

The Antibodies can be divided into two fragments;

• Fc: a homogenous portion which can be crystallized
• Antigen binding region: Fab2: this region of the antibody binds to antigens
  • This region consist of heavy and one of two types of light chains.

Basic structure of antibody

Specific features of antibodies

• Hinge regions: this regions provides the characteristic of flexibility that further enables the antibody to bind to the antigen
• In Fab, each heavy chain binds one of two different kinds of light chains; kappa and lambda
• There are five types of heavy chains recognized in humans and each of them are assigned a greek letter
  • Alpha Ά
  • Mu μ
  • Epsilon ε
  • Delta δ
  • Gamma γ
• There are five isotopes of antibodies, they differ from each based on the type of heavy chain present in Fab.
  • Immunoglobulin G : Gamma γ
  • Immunoglobulin A : Alpha Ά
  • Immunoglobulin M : Mu μ
  • Immunoglobulin E : Epsilon ε
  • Immunoglobulin D : Delta δ
• 

  Highlights the variable regions on Antibodies
  Variable domain : which consists of heterodimers of light chain and heavy chain and the function of this region is antigen binding
• Hyper variable regions : Constituents of these region are 100-110 amino acids.
  • Complementary determine region : present on each heavy and light chain, each chain contains three hyper variable regions.
  • This feature allows Ig to recognize a wide range of antigens
  • Two identical variable regions