Avidin nonspecific binding properties

Biotin modification reagents are widely used to attach a biotin group to proteins or other molecules for subsequent use in avidin, streptavidin, or NeutrAvidin separations or assays. Traditional biotin compounds containing aliphatic or other hydrophobic linker arms are discussed in detail in Chapter 11. In this section, the biotin-PEG compounds exclusively are discussed due to their unique hydrophilic properties, which include low nonspecific binding character and low immunogenicity. 

In some cases, the positively charged properties of egg-white avidin provide an advantage for its use in lieu of streptavidin. This is particularly the case when high levels of derivatization (for example in the synthesis of a fluorescent derivative of avidin) is required. Thus, the high number of free lysines in avidin furnishes an excellent medium for extensive derivatization with simultaneous reduction of the pi to an acceptable level. The use of nonglycosylated avidin for such purposes would counteract the other major source of nonspecific binding, i.e., saccharide-specific interactions. 

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