Chicken Avidin-related Protein 4/5 Shows Superior Thermal Stability when Compared with Avidin while Retaining High Affinity to Biotin.

The protein chicken avidin is a commonly used tool in various applications. The avidin gene belongs to a gene family that also includes seven other members known as the avidin-related genes (AVR). We report here on the extremely high thermal stability and functional characteristics of avidin-related protein AVR4/5, a member of the avidin protein family. The thermal stability characteristics of AVR4/5 were examined using a differential scanning calorimeter, microparticle analysis, and a microplate assay. Its biotin-binding properties were studied using an isothermal calorimeter and IAsys optical biosensor. According to these analyses, in the absence of biotin AVR4/5 is clearly more stable (Tm = 107.4 ± 0.3 °C) than avidin (Tm = 83.5 ± 0.1 °C) or bacterial streptavidin (Tm = 75.5 °C). AVR4/5 also exhibits a high affinity for biotin (Kd ≈ 3.6 × 10-14 M) comparable to that of avidin and streptavidin (Kd ≈ 10-15 M). Molecular modeling and site-directed mutagenesis were used to study the molecular details behind the observed high thermostability. The results indicate that AVR4]5 and its mutants have high potential as new improved tools for applications where exceptionally high stability and tight biotin binding are needed. [ABSTRACT FROM AUTHOR]