Streptavidin vs. Avidin — What's the Difference?

Streptavidin, derived from the bacterium Streptomyces avidinii, is known for its strong non-covalent binding to biotin, a vital nutrient. This characteristic makes it invaluable in biotechnological applications, especially in biochemical assays where precise biotin-streptavidin interactions are crucial. Unlike avidin, streptavidin lacks glycosylation, which reduces its non-specific binding to other molecules, enhancing its utility in research settings. Avidin, on the other hand, originates from egg whites and also exhibits a high affinity for biotin. Its natural role is to thwart bacterial growth by sequestering biotin, a vital nutrient for many organisms. Avidin's biotin-binding ability is exploited in various biochemical assays; however, its glycosylation can lead to higher non-specific binding compared to streptavidin. This property can sometimes limit its usefulness in certain scientific applications.

Both proteins are tetramers, meaning they consist of four subunits, which allow them to bind multiple biotin molecules simultaneously. This multivalency amplifies the sensitivity of detection methods in which they are used. However, the biotin-binding sites of avidin and streptavidin differ slightly, influencing their binding affinity and kinetics.

The difference in their source streptavidin from bacteria and avidin from egg whites—also reflects on their immunogenicity and potential applications. Streptavidin is generally preferred in applications requiring lower background noise due to its lack of glycosylation and hence, lower non-specific binding.

Despite their differences, both streptavidin and avidin find common ground in their pivotal role in biotechnological and diagnostic applications, leveraging their biotin-binding capabilities to facilitate a range of detection, purification, and labeling techniques.