Production of rapidly reversible antibody and its performance characterization as binder for continuous glucose monitoring

Discovery of a sulfated fucan-specific carbohydrate-binding module: The first member of a new carbohydrate-binding module family

Sulfated fucan is an important functional polysaccharide with various physiological activities. Carbohydrate-binding module (CBM) is a representative class of carbohydrate-binding protein, which could be employed as a favorable tool for the investigations and applications of polysaccharides. Nevertheless, only one confirmed sulfated fucan-binding CBM has been hitherto reported. In the present study, an unknown domain with a predicted β-sandwich fold was discovered from a fucanase Fun174A, and further cloned and heterologously expressed in Escherichia coli. The expressed protein Fun174A-CBM displayed a specific binding capacity to sulfated fucan. The bio-layer interferometry assays showed that the protein could bind to the sulfated fucan tetrasaccharide with an affinity constant of 2.83 × 10^-4 M. Fun174A-CBM shared no significant sequence similarity to any identified CBMs, indicating that it represents a new CBM family. The discovery of Fun174-CBM and the novel CBM family would be beneficial to the investigations of sulfated fucan-binding proteins.

Semi-automated single-molecule microscopy screening of fast-dissociating specific antibodies directly from hybridoma cultures

Fast-dissociating, specific antibodies are single-molecule imaging probes that transiently interact with their targets and are used in biological applications including image reconstruction by integrating exchangeable single-molecule localization (IRIS), a multiplexable super-resolution microscopy technique. Here, we introduce a semi-automated screen based on single-molecule total internal reflection fluorescence (TIRF) microscopy of antibody-antigen binding, which allows for identification of fast-dissociating monoclonal antibodies directly from thousands of hybridoma cultures. We develop monoclonal antibodies against three epitope tags (FLAG-tag, S-tag, and V5-tag) and two F-actin crosslinking proteins (plastin and espin). Specific antibodies show fast dissociation with half-lives ranging from 0.98 to 2.2 s. Unexpectedly, fast-dissociating yet specific antibodies are not so rare. A combination of fluorescently labeled Fab probes synthesized from these antibodies and light-sheet microscopy, such as dual-view inverted selective plane illumination microscopy (diSPIM), reveal rapid turnover of espin within long-lived F-actin cores of inner-ear sensory hair cell stereocilia, demonstrating that fast-dissociating specific antibodies can identify novel biological phenomena.

Purification and characterization of Fab fragments with rapid reaction kinetics against myoglobin

Myoglobin is an early biomarker for acute myocardial infarction. Recently, we isolated the antibody IgG-Myo2-7ds, which exhibits unique rapid reaction kinetics toward human myoglobin antigen. Antibodies with rapid dissociation kinetics are thought to be premature IgG forms that are produced during the early stage of in vivo immunization. In the present study, we identified the epitope region of the IgG-Myo2-7ds antibody to be the C-terminal region of myoglobin, which corresponds to 144-154 aa. The Fab fragment was directly purified by papain cleavage and protein G affinity chromatography and demonstrated kinetics of an association constant of 4.02 × 10(4) M(-1) s(-1) and a dissociation constant of 2.28 × 10(-2) s(-1), which retained the unique reaction kinetics of intact IgG-Myo2-7ds antibodies. Because a rapid dissociation antibody can be utilized for antibody recycling, the results from this study would provide a platform for the development of antibody engineering in potential diagnostic areas such as a continuous monitoring system for heart disease.

Refolded scFv antibody fragment against myoglobin shows rapid reaction kinetics

Myoglobin is one of the early biomarkers for acute myocardial infarction. Recently, we have screened an antibody with unique rapid reaction kinetics toward human myoglobin antigen. Antibodies with rapid reaction kinetics are thought to be an early IgG form produced during early stage of in vivo immunization. We produced a recombinant scFv fragment for the premature antibody from Escherichia coli using refolding technology. The scFv gene was constructed by connection of the V(H)-V(L) sequence with a (Gly4Ser)3 linker. The scFv fragment without the pelB leader sequence was expressed at a high level, but the solubility was extremely low. A high concentration of 8 M urea was used for denaturation. The dilution refolding process in the presence of arginine and the redox reagents GSH and GSSH successfully produced a soluble scFv protein. The resultant refolded scFv protein showed association and dissociation values of 9.32 × 10⁻⁴ M⁻¹·s⁻¹ and 6.29 × 10⁻³ s⁻¹, respectively, with an affinity value exceeding 10⁷ M⁻¹ (k(on)/k(off)), maintaining the original rapid reaction kinetics of the premature antibody. The refolded scFv could provide a platform for protein engineering for the clinical application for diagnosis of heart disease and the development of a continuous biosensor.

Semi-continuous, label-free immunosensing approach for Ca2+-based conformation change of a calcium-binding protein

Label-free immunosensing based on the conformational change of CBP depending on analyte concentration was explored for semi-continuous analysis of Ca²⁺.

Label-free, needle-type biosensor for continuous glucose monitoring based on competitive binding

With the goal of developing a method for the continuous monitoring of blood glucose, an implantable sensor was developed by placing an optical fiber probe within the internal hollow space of a syringe needle. A glucose binder, concanavalin A (Con A), was immobilized on the probe tip and a protein (e.g., bovine serum albumin) chemically coupled with a sugar ligand (e.g., mannose) was loaded as a solution inside of the needle, which were then closed using a semi-permeable membrane. Upon immersion in the glucose sample, small molecules were able to freely pass through the membrane and compete with the ligand conjugate for Con A binding. This changed the molecular layer thickness on the probe surfaces depending on the glucose concentration, which shifted the wavelength of the guided light along the fiber. Such interference in the wavelength pattern was measured using a commercial sensor system, Octet, without employing a label. Using this analytical approach, two major steps controlling the performance of glucose detection were overcome: permeation of glucose (optimum with 50 nm-porous polycarbonate membrane under the experimental conditioned used) and molecular diffusion of the ligand conjugate within the sensor compartment (19 gauge-needle, offering minimal demensions for the probe). Under optimal conditions, the sensor was able to monitor glucose fluctuations, even in serum medium, with a response time of less than 15 min in a range 10-500 mg/dL. This, however, could be further shortened down to about 5 min in principle by miniaturizing the sensor dimensions.