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Thursday, January 9, 2014

Avidin Biotin System


Avidin - Biotin systems are widely used in biochemical analysis and has got various applications in biotechnology and clinical medicine. The avidin-biotin system utilizes biotin, a low molecular weight vitamin, which can be chemically coupled to low or high molecular weight molecules such Protein, DNA or hormones. The biotin in its native or derivatized (having reporter probes ) form can be recognized by Avidin or streptavidin .



Avidin is a protein found in the egg white and streptavidin is found in stremptomyces avidinii. Both Avidin and Streptavidin has very high binding affinity towards the biotin.

Biotin is a low molecular weight vitamin commonly known as the vitamin H. Biotin has various roles in human body, first of all its an essential nutrient, biotin is also involved in the biosynthesis of fatty acids, gluconeogenesis, energy production and de novo synthesis of purines nucleotides.

Structure of Biotin


Structure of Biotin / Vitamin H

Biotin (C10H16N2O3S) has a Molecular Weight = 244.31 and is composed of
  • An ureido ring fused with a tetrahydrothiophene ring,
  • A valeric acid substituent attached to 1 of the 2 carbon atoms of the tetrahydrothiophene ring.
Biotin - Avidin Based Detetction System

Probes used in the Avidin-Biotin System

Probes Used can be prepared in two ways:

1. Chemically Coupled Probes
2. Biotinylated Probes

Chemically Coupled Probe
Avidin or streptavidin can be chemically coupled and are fluorescent, radioactive, or other types of macromolecules (proteins,polysaccharides, etc.).

Biotinylated ProbesOther method is to Biotinylate the probes and to make it interact them with streptavidin under sub-saturating ratios, thus leaving extra binding sites vacant.

More recently, fusion proteins have been prepared of streptavidin with different enzymes and native fluorescent proteins.

Which is best to use Avidin or Streptavidin?
Streptavidin is generally preffered over Avidin, because of its of neutral charge and lack of glycosylation. Nowadays various derivatives of avidin are available which are less expensive.

Types of Probes Used in the Avidin-Biotin System
  • Enzymes 
  • Radiolabels 
  • Flourescent Agents 
  • Chemilumniscent Agents 
  • Chromophores 
  • Heavy Metals 
  • Colloidal Gold 
  • Ferritin 
  • Hemocyanin 
  • Phages 
  • Macromolecular Carriers 
  • Liposomes 
  • Solid Support 
Applications of Avidin - Biotin System
  • Isolation Studies
  • Affinity Chromatography
  • Affinity Precipitation
  • Immobilizing Agents
  • Enzyme Reactor Systems
  • Selective retrieval
  • Selective Elimination
  • Diagnostics
  • Immunoassay
  • Signal Amplification
  • Blotting Technology
  • Bioaffinity Sensor
  • Gene probes
  • Chromosome Mapping
  • Affinity Cytochemistry
  • Localization Studies
  • Light Microscopy
  • Flourescence microscopy
  • Electron Microscopy
  • Histochemistry
  • Phage-display technology
  • Hybridoma Technology
  • Epitope Mapping
  • Cell Separation
  • Flow Cytometry
  • Fusogenic agent
  • Monolayer Technology
Advantages and Disadvantages of Avidin and Streptavidin
Advantage of Avidin is its ability of reversible interaction, in many applications reversible interaction is desired. Streptavidin has strong binding to Biotin which cannot be reserved can be disadvantageous. Avidin monomers can be immobilized and can be used for reversible interactions.

References:
Encyclopedia in Molecular Biology