What is the Difference Between Avidin and Streptavidin?

05/15/2025 • Felipe Moraes

Avidin and streptavidin are both proteins that have a high affinity and specificity for biotin. However, there are some differences between the two:

  1. Origin: Avidin is derived from the oviducts of birds, reptiles, and amphibians, while streptavidin is isolated from the bacterium Streptomyces avidinii.
  2. Structure: Avidin is a tetrameric glycoprotein with a molecular weight of approximately 62.4 kDa, while streptavidin is a slightly smaller molecule with a molecular weight of approximately 53.6 kDa and lacks the glycoprotein portion of the molecule.
  3. Sequence Homology: The sequence of avidin shows only 30% homology with streptavidin, and anti-avidin and anti-streptavidin antibodies are not immunologically cross-reactive.
  4. Binding Affinity: Avidin has a higher binding affinity for free biotin (Kd ~ 10^(-15) M) than streptavidin (Kd ~ 10^(-14) M). However, when biotin is conjugated to another molecule, streptavidin shows higher affinity than avidin.
  5. Non-specific Binding: Avidin has a higher tendency for aggregation and shows higher non-specific binding due to the glycoprotein portion of the molecule. Streptavidin, which lacks the glycoprotein portion, shows less non-specific binding.
  6. Applications: Both avidin and streptavidin have important applications in molecular biology and bio-nanotechnology, such as purification or detection of various molecules, Western blotting, and developing nanobiotechnology. However, due to its lower non-specific binding and higher affinity for biotin-conjugated molecules, streptavidin is often considered a better choice for biochemical applications.

Comparative Table: Avidin vs Streptavidin

Here is a table comparing avidin and streptavidin:

Feature Avidin Streptavidin
Origin Found in the oviducts of birds, reptiles, and amphibians Prepared from the purification of the bacterium Streptomyces avidinii
Molecular Weight 66,000 dalton glycoprotein 52,800 dalton protein
Isoelectric Point Highly cationic Near-neutral
Nonspecific Binding Exhibits nonspecific binding, sometimes causing background problems in histochemical applications and flow cytometry Reportedly exhibits less nonspecific binding than avidin
Glycosylation Glycosylated Not glycosylated
Biotinyl Ester Derivative Hydrolysis Has the ability to hydrolyze biotinyl ester derivatives Lacks the ability to hydrolyze biotinyl ester derivatives

Avidin and streptavidin are both proteins with high affinity and specificity for biotin. Avidin is a glycoprotein found in the oviducts of birds, reptiles, and amphibians, while streptavidin is a protein prepared from the purification of the bacterium Streptomyces avidinii. Avidin has a higher molecular weight and is highly cationic, while streptavidin has a near-neutral isoelectric point. Avidin exhibits nonspecific binding, which can sometimes cause background problems in certain applications, while streptavidin reportedly exhibits less nonspecific binding. Avidin is glycosylated, whereas streptavidin is not.

Read more