What is the Difference Between Avidin and Streptavidin?
🆚 Go to Comparative Table 🆚Avidin and streptavidin are both proteins that have a high affinity and specificity for biotin. However, there are some differences between the two:
- Origin: Avidin is derived from the oviducts of birds, reptiles, and amphibians, while streptavidin is isolated from the bacterium Streptomyces avidinii.
- 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.
- Sequence Homology: The sequence of avidin shows only 30% homology with streptavidin, and anti-avidin and anti-streptavidin antibodies are not immunologically cross-reactive.
- 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.
- 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.
- 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.
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