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

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

Similar to streptavidin, the binding of biotin by avidin does not appear to be cooperative in the traditional sense of altered binding strength, though it appears to be cooperative in terms of ligand induced structural communication across subunits in the protein as previously shown for streptavidin. In this work we provide data from intrinsic tryptophan fluorescence as evidence of a cooperative structural change. The technique involves examination of the changes in fluorescence emission corresponding to the various tryptophan populations accompanying avidin-biotin binding. We note that the 335 nm emission population (i.e. more hydrophobic local environment) saturates prior to full ligation and the saturation of the 350 nm emission population commonly used in standard binding activity assays. We also note that total integrated fluorescence emission and peak height during the titration of ligand into streptavidin also reach saturation prior to the 4:1 stoichiometric end point. Unique to avidin and distinct from the behavior of streptavidin described in our prior work, the wavelength of maximum emission and full width at half maximum (FWHM) data do not saturate prior to the 4:1 stoichiometric end point. Avidin also exhibited larger FWHM for both apo and holo forms suggesting greater heterogeneity in local tryptophan environments, as compared to streptavidin. Taken together, the data suggests that the binding of the first 3 biotins effect greater structural changes in the protein than the final ligand in a similar way for avidin and streptavidin.

Functionalization of a Fully Integrated Electrophotonic Silicon Circuit for Biotin Sensing

Electrophotonic (EPh) circuits are novel systems where photons and electrons can be controlled simultaneously in the same integrated circuit, attaining the development of innovative sensors for different applications. In this work, we present a complementary metal-oxide-semiconductor (CMOS)-compatible EPh circuit for biotin sensing, in which a silicon-based light source is monolithically integrated. The device is composed of an integrated light source, a waveguide, and a p-n photodiode, which are all fabricated in the same chip. The functionalization of the waveguide's surface was investigated to biotinylate the EPh system for potential biosensing applications. The modified surfaces were characterized by AFM, optical microscopy, and Raman spectroscopy, as well as by photoluminescence measurements. The changes on the waveguide's surface due to functionalization and biotinylation translated into different photocurrent intensities detected in the photodiode, demonstrating the potential uses of the EPh circuit as a biosensor.

Structural changes and molecular mechanism study on the inhibitory activity of epigallocatechin against α-glucosidase and α-amylase

In this study, the inhibition and mechanism of epigallocatechin (EGC) on two key glycoside hydrolases (α-glucosidase, α-amylase) were explored from the molecular structure level. The chemical structure of EGC was characterized by X-ray diffraction, Fourier transform infrared (FTIR) spectroscopy, and proton nuclear magnetic resonance spectroscopy. EGC's inhibition on these enzymes was colorimetrically determined. The effects of EGC on the chemical structure and spatial configuration of the enzymes were explored via FTIR spectroscopy, fluorescence spectroscopy, and molecular docking techniques. The results showed that EGC exhibited the inhibition of α-glucosidase and α-amylase in a non-competitive manner, showing a continuous upward trend as EGC's concentration increased. There was a fluorescence quenching effect of EGC on α-glucosidase and α-amylase. Molecular docking confirmed that EGC can bind to amino acid residues in the enzyme through intermolecular hydrogen bonds and hydrophobic interactions, resulting in the changed chemical structure and spatial conformation of the enzymes. This decreased enzyme activity. This result suggested that EGC has the potential to inhibit two key glycoside hydrolases, and it would be beneficial to incorporate EGC into functional foods for diabetics.

Cytosolic Protein Delivery Using Modular Biotin-Streptavidin Assembly of Nanocomposites

Current strategies for the delivery of proteins into cells face general challenges of endosomal entrapment and concomitant degradation of protein cargo. Efficient delivery directly to the cytosol overcomes this obstacle: we report here the use of biotin-streptavidin tethering to provide a modular approach to the generation of nanovectors capable of a cytosolic delivery of biotinylated proteins. This strategy uses streptavidin to organize biotinylated protein and biotinylated oligo(glutamate) peptide into modular complexes that are then electrostatically self-assembled with a cationic guanidinium-functionalized polymer. The resulting polymer-protein nanocomposites demonstrate efficient cytosolic delivery of six biotinylated protein cargos of varying size, charge, and quaternary structure. Retention of protein function was established through efficient cell killing via delivery of the chemotherapeutic enzyme granzyme A. This platform represents a versatile and modular approach to intracellular delivery through the noncovalent tethering of multiple components into a single delivery vector.

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

Multimeric protein assemblies are abundant in nature. Streptavidin is an attractive protein that provides a paradigm system to investigate the intra- and intermolecular interactions of multimeric protein complexes. Also, it offers a versatile tool for biotechnological applications. Here, we present two apo-streptavidin structures, the first one is an ambient temperature Serial Femtosecond X-ray crystal (Apo-SFX) structure at 1.7 Å resolution and the second one is a cryogenic crystal structure (Apo-Cryo) at 1.1 Å resolution. These structures are mostly in agreement with previous structural data. Combined with computational analysis, these structures provide invaluable information about structural dynamics of apo streptavidin. Collectively, these data further reveal a novel cooperative allostery of streptavidin which binds to substrate via water molecules that provide a polar interaction network and mimics the substrate biotin which displays one of the strongest affinities found in nature.