What is the Difference Between Avidin and Streptavidin

The key difference between avidin and streptavidin is that avidin has a high affinity and specificity for biotin but comparatively less affinity than streptavidin because streptavidin-biotin is one of the strongest complexes having a non-covalent bond.

Avidin is a type of protein that forms in the oviducts of birds, reptiles, and amphibians. Streptavidin is a type of protein that is prepared from the purification of the bacterium Streptomyces avidinii.

CONTENTS

1. Overview and Key Difference
2. What is Avidin 
3. What is Streptavidin 
4. Avidin vs Streptavidin in Tabular Form
5. Summary – Avidin vs Streptavidin 

What is Avidin?

Avidin is a type of protein that forms in the oviducts of birds, reptiles, and amphibians. This protein is a tetrameric biotin-binding protein that deposits in the whites of eggs. There are dimeric members of avidin in addition to tetrameric forms. We can find these dimeric forms in some bacteria. When considering chicken egg white, it has about 0.05% of avidin in relation to the total protein content.

There are four identical subunits in the tetrameric protein. Therefore, we can call it a homotetramer. Each tetramer can bind with biotin (also named vitamin B7). The affinity and specificity of this binding are very high. Avidin-biotin complex is one of the strongest known non-covalent bonds.

We can find functional avidin in raw eggs. When cooked, the biotin affinity for avidin gets destroyed. However, the natural function of the avidin egg is not yet known exactly. Scientists have postulated that this protein forms in the oviduct of the egg as a bacterial growth inhibitor. It can bind with biotin (biotin is helpful for bacterial growth).

Moreover, there is a non-glycosylated form of avidin available as a commercial product. It is still unknown whether this non-glycosylated form occurs naturally or not. There are some important applications of this protein, including research applications, biochemical assays, purification media, etc.

What is Streptavidin?

Streptavidin is a type of protein that is prepared from the purification of the bacterium Streptomyces avidinii. It is a tetramer. There are homo-tetramers of streptavidin having an extraordinarily high affinity for biotin. It is known that the binding of biotin to streptavidin is one of the strongest non-covalent interactions in nature. This protein is useful in molecular biology and bio-nanotechnology due to the resistance of the streptavidin-biotin complex towards organic solvents, denaturants, proteolytic enzymes, extreme temperatures, pH values, and detergents.

There are important applications of streptavidin such as purification or detection of various biomolecules, purification, and detection of genetically modified peptides, in Western blotting, developing Nanobiotechnology, etc.

What is the Difference Between Avidin and Streptavidin?

Avidin is a type of protein that forms in the oviducts of birds, reptiles, and amphibians. Streptavidin is a type of protein that is prepared from the purification of the bacterium Streptomyces avidinii. The key difference between avidin and streptavidin is that avidin has a high affinity and specificity for biotin but comparatively less affinity than streptavidin because streptavidin-biotin is one of the strongest complexes having a non-covalent bond.

The below infographic presents the differences between avidin and streptavidin in tabular form for side by side comparison.

Summary – Avidin vs Streptavidin

Avidin and streptavidin are important proteins. The key difference between avidin and streptavidin is that avidin has a high affinity and specificity for biotin but comparatively less affinity than streptavidin because streptavidin-biotin is one of the strongest complexes having a non-covalent bond.

Reference:

1. “Biotinylation.” Thermo Fisher Scientific – US.

Image Courtesy:

1. “Tetramer” By Oxford grad at English Wikipedia (CC BY-SA 3.0) via Commons Wikimedia
2. “Streptavidin” By Roo1812 (picture), Weber, P.C., Ohlendorf, D.H., Wendoloski, J.J., Salemme, F.R. (Data used) – Own work, using PDB: 1STP​ (Public Domain) via Commons Wikimedia