Rapid, high-yield recovery of a recombinant digoxin binding single chain Fv from Escherichia coli

Design of a Phenotypic Sensor About Protein and Moisture in Wheat Grain

A near-infrared (NIR) spectrometer can perceive the change in characteristics of the grain reflectance spectrum quickly and nondestructively, which can be used to determine grain quality information. The full-band spectral information of samples of multiple physical states can be measured using existing instruments, yet it is difficult for the full-band instrument to be widely used in grain quality detection due to its high price, large size, non-portability, and inability to directly output the grain quality information. Because of the above problems, a phenotypic sensor about grain quality was developed for wheat, and four wavelengths were chosen. The interference of noise signals such as ambient light was eliminated by the phenotypic sensor using the modulated light signal and closed sample pool, the shape and size of the incident light spot of the light source were determined according to the requirement for collecting the reflectance spectrum of the grain, and the luminous units of the light source with stable light intensity and balanced luminescence were developed. Moreover, the sensor extracted the reflectance spectrum information using a weak optical signal conditioning circuit, which improved the resolution of the reflectance signal. A grain quality prediction model was created based on the actual moisture and protein content of grain obtained through Physico-chemical analyses. The calibration test showed that the R² of the relative diffuse reflectance (RDR) of all four wavelengths of the phenotypic sensor and the reflectance of the diffusion fabrics were higher than 0.99. In the noise level and repeatability tests, the standard deviations of the RDR of two types of wheat measured by the sensor were much lower than 1.0%, indicating that the sensor could accurately collect the RDR of wheat. In the calibration test, the root mean square errors (RMSE) of protein and moisture content of wheat in the Test set were 0.4866 and 0.2161%, the mean absolute errors (MAEs) were 0.6515 and 0.3078%, respectively. The results showed that the NIR phenotypic sensor about grain quality developed in this study could be used to collect the diffuse reflectance of grains and the moisture and protein content in real-time.

History, mechanism of action, and toxicity: a review of commonly used dough rheology improvers

Dough rheology improvers, which often are oxidative reagents in nature, have long been used in bread-making industry to enhance protein crosslinking and subsequently improve the dough rheological properties and bread qualities. Numerous studies were conducted to explore the effects of these oxidative agents on dough quality improving, however, the underlying mechanism of their action during dough development has not been fully understood. Due to the public health concerns, multiple oxidative reagents were banned in some countries across the world, while others are still permitted in accordance with regulations. Therefore, a comprehensive understanding of their application, significance, and safety in bread manufacturing is necessary. This review aims to provide a detailed information about the evolutionary history of several commonly used oxidants acting as dough rheology improvers, their mechanisms of action, as well as their potential toxicity.

Microcalorimetric Study of the Effect of Hexa-histidine Tag and Denaturant on the Interaction Mechanism between Protein and Metal-Chelating Gel

A recombinant protein, Schistosoma japonicum glutathione-S-transferase (SjGST), was fused with a C-terminal hexa-histidine tag to obtain SjGST/His. Both proteins were used to probe the interaction mechanisms with the metal ions immobilized on chromatography gels. Isothermal titration calorimetry was used to directly measure the adsorption enthalpies (DeltaH(ads)) of both proteins with Ni-NTA and TALON (Co(2+)) commercial affinity resins, under the conditions of with and without the presence of a denaturant. The result reveals that SjGST/His had a lower DeltaH(ads) value with Ni-NTA than did SjGST, mainly attributed to the formation of more coordination bonds with or a stronger binding with Ni-NTA. Furthermore, the difference between the DeltaH(ads) values of SjGST/His onto TALON under the nature and denaturing conditions were insignificant, implying that the binding topography of the hexa-histidine tail with immobilized Co(2+) was not significantly changed with the presence of a denaturant. In addition, this study shows that the proposed binding models and the directly measured adsorption heat can be combined to elucidate the difference in the interaction mechanisms of SjGST/His adsorption onto those two adsorbents from a thermodynamic perspective. Copyright 2001 Academic Press.

Noncompetitive immunoassay of small analytes at the femtomolar level by affinity probe capillary electrophoresis: direct analysis of digoxin using a uniform-labeled scFv immunoreagent

A general method for noncompetitive immunoassay of small analytes using affinity probe capillary electrophoresis (APCE) is demonstrated using digoxin as a model analyte. A uniform immunoreagent was prepared from a single-chain antibody (scFv) gene specific for digoxin. Site-directed mutagenesis introduced a unique cysteine residue for uniform labeling with a thiol-reactive fluorochrome. After expression in E. coli, the scFv was purified by immobilized metal affinity chromatography (IMAC) using an added C-terminal 6-histidine sequence. The protein was renatured and labeled while immobilized on the IMAC resin. After 0.02-microm filtration to remove microaggregates, the resulting reagent was highly uniform and stable at -12 degrees C for at least 1 year. Three formats of APCE using the scFv reagent were explored. A "mix-and-inject" assay optimized for low detection limits demonstrated analysis of 10 pM digoxin in aqueous standard solutions in 10 min. A rapid mix-and-inject format in a short capillary allowed detection of 1 nM digoxin in 1 min. Digoxin samples in serum and urine were injected directly after 10-fold dilution. In combination with solid-phase extraction, 400 fM digoxin was detected in 1 mL of serum. Including solid-phase extraction, reproducibility was within 2.5%, and the linear range was 3 orders of magnitude. The strategy adopted in this paper should be of general use in the low-level analysis of small analytes.

In vitro scanning saturation mutagenesis of all the specificity determining residues in an antibody binding site

For the first time, each specificity determining residue (SDR) in the binding site of an antibody has been replaced with every other possible single amino acid substitution, and the resulting mutants analyzed for binding affinity and specificity. The studies were conducted on a variant of the 26-10 antidigoxin single chain Fv (scFv) using in vitro scanning saturation mutagenesis, a new process that allows the high throughput production and characterization of antibody mutants [Burks,E.A., Chen,G., Georgiou,G. and Iverson,B.L. (1997) Proc. Natl Acad. Sci. USA, 94, 412-417]. Single amino acid mutants of 26-10 scFv were identified that modulated specificity in dramatic fashion. The overall plasticity of the antibody binding site with respect to amino acid replacement was also evaluated, revealing that 86% of all mutants retained measurable binding activity. Finally, by analyzing the physical properties of amino acid substitutions with respect to their effect on hapten binding, conclusions were drawn regarding the functional role played by the wild-type residue at each SDR position. The reported results highlight the value of in vitro scanning saturation mutagenesis for engineering antibody binding specificity, for evaluating the plasticity of proteins, and for comprehensive structure-function studies and analysis.

Microcalorimetric Studies of the Interactions of Lysozyme with Immobilized Cu(II): Effects of pH Value and Salt Concentration

In this investigation, employing a highly sensitive microcalorimeter, we measure the influence of pH value and salt concentration on the heat of interaction between lysozyme and CS-IDA-Cu(II) gel. The direct enthalpy measurement of the interaction provides thermodynamic information regarding the binding behavior of lysozyme toward the immobilized metal ion. The binding enthalpy altered by adsorbed lysozyme at various pH values and salt concentrations are measured. The findings, along with the reported binding isotherm, are discussed herein.

In vitro scanning saturation mutagenesis of an antibody binding pocket

We have combined PCR mutagenesis with in vitro transcription/translation and ELISA for the rapid generation and characterization of antibody mutants. The PCR products are used directly as the template for the in vitro transcription/translation reactions and because no cloning steps are required, the in vitro saturation mutagenesis of one residue can be completed in duplicate within a week by a single investigator. In vitro scanning saturation mutagenesis was used to analyze the role and plasticity of six key contact residues (H:Tyr-33, H:Asn-35, H:Tyr-50, H:Trp-100, L:Val-94, and L:Pro-96) in the binding pocket of a single chain Fv antibody derived from the 26-10 monoclonal antibody. A total of 114 mutant antibodies were produced; all 19 substitutions at each of the 6 chosen positions. The mutants were analyzed for binding to digoxin, digitoxin, digoxigenin, and ouabain resulting in the generation of a comprehensive data base of 456 relative affinity values. Excellent agreement between the relative affinity values obtained with in vitro synthesized mutant antibodies and equilibrium affinity data obtained with previously reported purified mutant monoclonal antibodies was observed. Approximately 75% of the single amino acid mutants exhibited significant binding to one or more of the digoxin analogs. Mutations that alter and, in some cases, reverse specificity for the different digoxin analogs were identified. In vitro scanning saturation mutagenesis represents a new tool for protein structure-function and engineering studies and can be interfaced with laboratory automation so that an even higher throughput of protein mutants can be constructed and analyzed.

High-level expression in insect cells and purification of secreted monomeric single-chain Fv antibodies

We have constructed a recombinant baculovirus encoding an anti-(phenyl-oxazolone) single-chain Fv antibody (anti-phOx-scFv) fused to the baculovirus GP67 secretion signal sequence, 6 liters of Sf9 insect cells were infected with this virus at a multiplicity of infection of one and cultured in a bioreactor for 72 h. The dialyzed supernatant was subjected to cation exchange chromatography at pH 6.0 followed by size exclusion chromatography on a Sephadex G100 superfine matrix. This rapid protocol resulted in the isolation of monomeric scFv with a purity of greater than 98%. The final yield was 32 mg/l (10(9) cells/l). Partial amino-terminal sequencing revealed that the GP67 signal sequence was completely removed upon secretion. The dissociation constant of the scFv monomers is about 1 x 10(-4) M. By competitive ELISA scFv dimers yielded a half maximum inhibitory concentration of 3.4 x 10(-7 M which matches the earlier measured Kd for the anti-phOx-scFv (3.2-5.3 x 10-7 M. Marks et al. (1991) J. Mol. Biol. 222, 581-597: Marks et al. (1992) Bio/Technology 10, 779-783). This method is readily scaled up for the preparation of scFv antibodies in high yield and purity obviating any affinity chromatography and/or refolding steps by exploitation of insect cell expression as an efficient alternative to E. coli expression.