Streptavidin cooperative allosterism upon binding biotin observed by differential changes in intrinsic fluorescence

Abstract

While the binding of biotin by streptavidin does not appear to be cooperative in the traditional sense of altered binding strength, it has been suggested that it may be cooperative in terms of differential structural changes in the protein. In this work we present intrinsic tryptophan fluorescence data as evidence of a cooperative structural change. The technique involves examination of the differences in fluorescence emission corresponding to distinct tryptophan populations accompanying protein-ligand binding. Specifically we note that the 335 nm emission population (i.e. more hydrophobic) saturates prior to the saturation of the 350 nm emission population commonly used in the standard binding activity assay. We also note that the wavelength of maximum emission, total integrated fluorescence emission and full width at half maximum during the titration of ligand into streptavidin also reach saturation before the expected 4:1 stoichiometric end point. This suggests that the binding of the first 3 biotins effect greater structural changes in the protein than the final ligand.

Cooperative allostery and structural dynamics of streptavidin at cryogenic- and ambient-temperature

“…8e). Although a previous study indicated that the binding of biotin is not cooperative according to principal component analysis 44 , these results confirm that biotin binding may not have a stabilizing effect but can cause the allosteric response of streptavidin 23 . Also, biotin binding may affect other dimer chains of the tetrameric structure and provide cooperativity for additional ligand binding by perturbing active site residues.…”

“…Our data suggest that this structural feature is intermolecular allostery between monomers of streptavidin. Recently, a new model was proposed to describe structural cooperativity of streptavidin and a cooperative allosterism upon binding biotin 23 . Ligand binding is characterized by L3/4.…”

“…Along with two opposing views, it was also suggested that the streptavidin-biotin interaction showed positive cooperativity, and the cooperativity of the tetramer was accompanied by closeness of the streptavidin upon biotin binding 21,22 . Later on, this phenomenon was named "cooperative allosterism" 23 . Streptavidin-biotin complex has numerous applications and many of them are investigated structurally.…”

Cooperative Allostery and Structural Dynamics of Streptavidin at Cryogenic- and Ambient-temperature

“…8e) . Although a previous study indicated that the binding of biotin is not cooperative according to PCA analysis [44], these results confirm biotin binding may not have a stabilizing effect but can cause the allosteric response of streptavidin [23]. Also, biotin binding may affect other dimer chains of the tetrameric structure and provide cooperativity for additional ligand binding by perturbing active site residues.…”

“…Along with two opposing views, it was also suggested that the streptavidin-biotin interaction showed positive cooperativity, and the cooperativity of the tetramer was accompanied by closeness of the streptavidin upon biotin-binding [21,22]. Later on, this phenomenon was named "cooperative allosterism" [23]. Streptavidin-biotin complex has numerous applications and many of them are investigated structurally.…”