Extremely high thermal stability of streptavidin and avidin upon biotin binding

GONZÁLEZ, M.,; ARGARAÑA CE; FIDELIO, G.D

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Año: 1999 vol. 16 p. 67 - 67

he effect of biotin binding on the thermal stability of streptavidin (STV) and avidin (AVD) was evaluated using differential scanning calorimetry. Biotin binding increases the midpoint of temperature Tm of thermally induced denaturation of STV and AVD in phosphate buffer from 75 and 83°C to 112 and 117°C at full biotin saturation, respectively. This thermostability is the highest reported for proteins coming from either mesophilic or thermophilic organisms. In both proteins, biotin also increases the calorimetric enthalpy and the cooperativity of the unfolding. Thermal stability of STV was also evaluated in the presence of high concentrations of urea or guanidinium hydrochloride (GuHCl). In 6 M GuHCl, STV remains as a tetramer and the Tm of the STV-biotin complex is centered at 108°C, a few degrees below the value obtained in phosphate buffer. On the contrary, STV under fully saturating condition remains mainly in its dimeric form in 8 M urea and the thermogram shows two endotherms. T