Reversibility of biotin-binding by selective modification of tyrosine in avidin.
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ABSTRACT:
SUBMITTER: Morag E
PROVIDER: S-EPMC1217322 | biostudies-other | 1996 May
REPOSITORIES: biostudies-other
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Project description:The binding of biotin to avidin is one of the strongest in nature with absolute free energy of binding, ?A(0) = -20.4 kcal/mol. Therefore, this complex became a target for a large number of computational studies, which all, however, are based on approximate techniques or simplified models and have led to a wide range of results Therefore, ?A(0) is calculated here by rigorous statistical mechanical methods and models that consider long-range electrostatics. (1) We apply our method, "hypothetical scanning molecular dynamics with thermodynamic integration" (HSMD-TI) to avidin-biotin modeled by periodic boundary conditions with particle mesh ewald (PME). (2) We apply the double decoupling method (DDM) to this system modeled by the spherical solvent boundary potential (SSBP) and the generalized solvent boundary potential (GSBP). The corresponding results for neutral biotin, ?A(0) = -29.1 ± 0.8 and -25.2 ± 0.5 kcal/mol are significantly lower than the experimental value; we also provide the result for a charged biotin, ?A(0) = -33.3 ± 0.8 kcal/mol. It is plausible to suggest that this disagreement with the experiment may stem from ignoring the (positive) contribution of a mobile loop that changes its structure upon ligand binding.
| S-EPMC3383089 | biostudies-literature
Project description:The involvement of tyrosine in the biotin-binding sites of the egg-white glycoprotein avidin and the bacterial protein streptavidin was examined by using the tyrosine-specific reagent p-nitrobenzenesulphonyl fluoride (Nbs-F). Modification of an average of about 0.5 mol of tyrosine residue/mol of avidin subunit caused the complete loss of biotin binding. This indicates that the single tyrosine residue (Tyr-33) in the avidin subunit is directly involved in the biotin-binding site and that its modification by Nbs also abolishes the binding properties of a neighbouring subunit. This suggests that the tyrosine residues of the egg-white protein may also contribute to the stabilization of the native protein structure. In streptavidin, however, the modification of an average of 3 mol of tyrosine residue/mol of subunit was required to inactivate completely the biotin-binding activity of the protein, but only 1 mol (average) of tyrosine residue/mol of subunit was protected in the presence of biotin. The difference between the h.p.l.c. elution profiles of the enzymic digests of Nbs-modified streptavidin and the Nbs-modified streptavidin-biotin complex revealed two additional fractions in the unprotected protein that contain Nbs-modified tyrosine residues. These residues, Tyr-43 (major fraction) and Tyr-54 (minor fraction), appear to contribute to the biotin-binding site in streptavidin.
| S-EPMC1131609 | biostudies-other
Project description:Mesenchymal stem cells (MSCs) have various functions, making a significant contribution to tissue repair. On the other hand, the viability and function of MSCs are not lasting after an in vivo transplant, and the therapeutic effects of MSCs are limited. Although various chemical modification methods have been applied to MSCs to improve their viability and function, most of conventional drug modification methods are short-term and unstable and cause cytotoxicity. In this study, we developed a method for long-term drug modification to C3H10T1/2 cells, murine mesenchymal stem cells, without any damage, using the avidin-biotin complex method (ABC method). The modification of NanoLuc luciferase (Nluc), a reporter protein, to C3H10T1/2 cells by the ABC method lasted for at least 14 days in vitro without major effects on the cellular characteristics (cell viability, cell proliferation, migration ability, and differentiation ability). Moreover, in vivo, the surface Nluc modification to C3H10T1/2 cells by the ABC method lasted for at least 7 days. Therefore, these results indicate that the ABC method may be useful for long-term surface modification of drugs and for effective MSC-based therapy.
| S-EPMC5717103 | biostudies-literature
Project description:BackgroundA chicken egg contains several biotin-binding proteins (BBPs), whose complete DNA and amino acid sequences are not known. In order to identify and characterise these genes and proteins we studied chicken cDNAs and genes available in the NCBI database and chicken genome database using the reported N-terminal amino acid sequences of chicken egg-yolk BBPs as search strings.ResultsTwo separate hits showing significant homology for these N-terminal sequences were discovered. For one of these hits, the chromosomal location in the immediate proximity of the avidin gene family was found. Both of these hits encode proteins having high sequence similarity with avidin suggesting that chicken BBPs are paralogous to avidin family. In particular, almost all residues corresponding to biotin binding in avidin are conserved in these putative BBP proteins. One of the found DNA sequences, however, seems to encode a carboxy-terminal extension not present in avidin.ConclusionWe describe here the predicted properties of the putative BBP genes and proteins. Our present observations link BBP genes together with avidin gene family and shed more light on the genetic arrangement and variability of this family. In addition, comparative modelling revealed the potential structural elements important for the functional and structural properties of the putative BBP proteins.
| S-EPMC1082904 | biostudies-literature
Project description:The object of this study was to define minimized biotin-binding fragments, or 'prorecognition sites', of either the egg-white glycoprotein avidin or its bacterial analogue streptavidin. Because of the extreme stability to enzymic hydrolysis, fragments of avidin were prepared by chemical means and examined for their individual biotin-binding capacity. Treatment of avidin with hydroxylamine was shown to result in new cleavage sites in addition to the known Asn-Gly cleavage site (position 88-89 in avidin). Notably, the Asn-Glu and Asp-Lys peptide bonds (positions 42-43 and 57-58 respectively) were readily cleaved; in addition, lesser levels of hydrolysis of the Gln-Pro (61-62) and Asn-Asp (12-13 and 104-105) bonds could be detected. The smallest biotin-binding peptide fragment, derived from hydroxylamine cleavage of either native or non-glycosylated avidin, was identified to comprise residues 1-42. CNBr cleavage resulted in a 78-amino acid-residue fragment (residues 19-96) that still retained activity. The data ascribe an important biotin-binding function to the overlapping region (residues 19-42) of avidin, which bears the single tyrosine moiety. This contention was corroborated by synthesizing a tridecapeptide corresponding to residues 26-38 of avidin; this peptide was shown to recognize biotin. Streptavidin was not susceptible to either enzymic or chemical cleavage methods used in this work. The approach taken in this study enabled the experimental distinction between the chemical and structural elements of the binding site. The capacity to assign biotin-binding activity to the tyrosine-containing domain of avidin underscores its primary chemical contribution to the binding of biotin by avidin.
| S-EPMC1151383 | biostudies-other
Project description:Affinity interactions between the small molecule biotin and the protein avidin have been used extensively to functionalize biomaterials. More recently, researchers have leveraged the changes in biotin-avidin affinity that occur upon biotin conjugation to larger molecules to control the release of biotinylated drugs and proteins. However, the effects of biotin-avidin interactions on hydrogel properties have not been thoroughly investigated. The objective of this study was to evaluate the effect of increasing biotin and avidin concentrations on hydrogel swelling properties, as an indicator of crosslinking. Gelatin, selected as a model hydrogel material, was biotinylated at increasing fold molar excesses of biotin with a PEG linker using N-hydroxysuccinimide chemistry. Afterwards, biotinylated gelatin was formed into hydrogels and stabilized with glutaraldehyde. Swelling properties of the biotinylated hydrogels were investigated by conducting swelling studies in different avidin solutions. Increasing the degree of biotinylation caused significant decreases in swelling ratios of the hydrogels in a dose-dependent manner, suggesting increases in crosslinking of the hydrogels. However, increasing avidin concentrations in excess of biotin content did not significantly affect swelling ratios. Moving hydrogels to phosphate-buffered saline following avidin incorporation resulted in increased swelling ratios for hydrogels prepared with a lower concentration of biotin. However, hydrogels prepared with the highest concentration of biotin did not experience increased swelling ratios, implying that the stability of biotin-avidin-mediated crosslinking depends on the number of biotin molecules available for binding. Collectively, these results demonstrate that biotin-avidin interactions control hydrogel swelling properties, and that the magnitude and stability of the effects depend on the biotin concentration. These results have important implications for affinity-based controlled release of biotinylated drugs or proteins from biotin-avidin-crosslinked hydrogels.
| S-EPMC7711042 | biostudies-literature
Project description:In this work the synthesis, photochemistry, and streptavidin interaction of new [Ru(tpy)(bpy)(SRR')](PF6)2 complexes where the R' group contains a free biotin ligand, are described. Two different ligands SRR' were investigated: An asymmetric ligand 1 where the Ru-bound thioether is a N-acetylmethionine moiety linked to the free biotin fragment via a triethylene glycol spacer and a symmetrical ligand 2 containing two identical biotin moieties. The coordination of these two ligands to the precursor [Ru(tpy)(bpy)Cl]Cl was studied in water at 80 °C. In such conditions the coordination of the asymmetric ligand 1 occurred under thermodynamic control. After the reaction, a mononuclear and a binuclear complex were isolated. In the mononuclear complex, the ratio of methionine- {[6](PF6)2} vs. biotin-bound {[7](PF6)2} regioisomer was 5.3 and the free biotin fragment of [6](PF6)2 allowed to purify it from its isomer [7](PF6)2 at small scales using avidin affinity chromatography. Coordination of the symmetrical ligand 2 afforded [Ru(tpy)(bpy)(2)](PF6)2 {[8](PF6)2} in synthetically useful scales (100 mg), good yield (82 %), and without traces of the binuclear impurity. In this complex, one of the biotin remains free whereas the second one is coordinated to ruthenium. Photochemical release of ligand 2 from [8](PF6)2 occurred upon blue light irradiation (465 nm) with a photosubstitution quantum yield of 0.011 that was independent of the binding of streptavidin to the free biotin ligand.
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Project description:Chicken avidin and bacterial streptavidin are proteins familiar from their use in various (strept)avidin-biotin technological applications. Avidin binds the vitamin biotin with the highest affinity known for non-covalent interactions found in nature. The gene encoding avidin (AVD) has homologues in chicken, named avidin-related genes (AVRs). In the present study we used the AVR genes to produce recombinant AVR proteins (AVRs 1, 2, 3, 4/5, 6 and 7) in insect cell cultures and characterized their biotin-binding affinity and biochemical properties. Amino acid sequence analysis and molecular modelling were also used to predict and explain the properties of the AVRs. We found that the AVR proteins are very similar to avidin, both structurally and functionally. Despite the numerous amino acid substitutions in the subunit interface regions, the AVRs form extremely stable tetramers similar to those of avidin. Differences were found in some physico-chemical properties of the AVRs as compared with avidin, including lowered pI, increased glycosylation and, most notably, reversible biotin binding for two AVRs (AVR1 and AVR2). Molecular modelling showed how the replacement Lys(111)-->isoleucine in AVR2 alters the shape of the biotin-binding pocket and thus results in reversible binding. Both modelling and biochemical analyses showed that disulphide bonds can form and link monomers in AVR4/5, a property not found in avidin. These, together with the other properties of the AVRs described in the present paper, may offer advantages over avidin and streptavidin, making the AVRs applicable for improved avidin-biotin technological applications.
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Project description:1. The reaction between avidin and biotin was found to be exothermic, DeltaH being -20.3kcal./mole of biotin bound. The corresponding value of DeltaH for streptavidin was -23kcal./mole. 2. The heat evolved was independent of the pH (between 5 and 9), of the buffer (borate or ammonia) and of the fractional saturation of the avidin with biotin. 3. The entropy change for the reaction was zero, and it is suggested that the entropy increase to be expected from hydrophobic interactions was counterbalanced by a decrease in entropy accompanying the formation of buried hydrogen bonds. 4. Modification of the potential hydrogen-bonding sites of the imidazolidone ring led to a decreased heat output and a positive entropy of reaction.
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Project description:Developing magnetic resonance imaging (MRI) contrast agents with high relaxivity and specificity was essential to increase MRI diagnostic sensitivity and accuracy. In this study, the MRI contrast agent, vascular endothelial growth factor receptor (VEGFR)-targeted poly (l-lysine) (PLL)-diethylene triamine pentacetate acid (DTPA)-gadolinium (Gd) (VEGFR-targeted PLL-DTPA-Gd, VPDG), was designed and prepared to enhance the MRI diagnosis capacity of tumor. Biotin-PLL-DTPA-Gd was synthesized first, then, VEGFR antibody was linked to biotin-PLL-DTPA-Gd using biotin-avidin reaction. In vitro cytotoxicity study results showed that VPDG had low toxicity to MCF-7 cells and HepG2 cells at experimental concentrations. In cell uptake experiments, VPDG could significantly increase the internalization rates (61.75%±5.22%) in VEGFR-positive HepG2 cells compared to PLL-DTPA-Gd (PDG) (25.16%±4.71%, P<0.05). In MRI studies in vitro, significantly higher T1 relaxivity (14.184 mM-1 s-1) was observed compared to Magnevist® (4.9 mM-1 s-1; P<0.01). Furthermore, in vivo MRI study results showed that VPDG could significantly enhance the tumor signal intensity and prolong the diagnostic time (from <1 h to 2.5 h). These results indicated that macromolecular VPDG was a promising MRI contrast agent and held great potential for molecular diagnosis of tumor.
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