[Show abstract][Hide abstract] ABSTRACT: In antibody purification processes, the acidic buffer commonly used to elute the bound antibodies during conventional affinity chromatograph, can damage the antibody. Herein we describe the development of several types of affinity ligands which enable the purification of antibodies under much milder conditions.
[Show abstract][Hide abstract] ABSTRACT: The understanding of how primordial proteins emerged has been a fundamental and longstanding issue in biology and biochemistry. For a better understanding of primordial protein evolution, we synthesized an artificial protein on the basis of an evolutionary hypothesis: segment-based elongation starting from an autonomously foldable short peptide. A 10-residue protein, chignolin, the smallest foldable polypeptide ever reported, was used as a structural support to facilitate higher structural organization and gain-of-function in the development of an artificial protein. Repetitive cycles of segment elongation and subsequent phage display selection successfully produced a 25-residue protein, termed AF.2A1, with nanomolar affinity against the Fc region of immunoglobulin G. AF.2A1 shows exquisite molecular recognition ability such that it can distinguish conformational differences of the same molecule. The structure determined by NMR measurements demonstrated that AF.2A1 forms a globular protein-like conformation with the chignolin-derived β-hairpin and a tryptophan-mediated hydrophobic core. Using sequence analysis and a mutation study, we discovered that the structural organization and gain-of-function emerged from the vicinity of the chignolin segment, revealing that the structural support served as the core in both structural and functional development. Here, we propose an evolutionary model for primordial proteins in which a foldable segment serves as the evolving core to facilitate structural and functional evolution. This study provides insights into primordial protein evolution and also presents a novel methodology for designing small sized proteins useful for industrial and pharmaceutical applications.
Journal of Biological Chemistry 12/2013; · 4.65 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Optimizing antibody purification is crucial to overcoming a bottleneck in the costly manufacturing process for antibody therapy. To address this issue, we designed a pH-sensitive Staphylococcus aureus protein A variant that retained its innate stability and affinity toward antibody. On the basis of structural information and mutation analysis data, we identified candidate positions for accumulative histidine substitutions to cause electrostatic repulsion under acidic conditions. The histidine substitutions effectively decreased the dissociation rate under acidic conditions by three orders of magnitude. Avoiding deleterious effects of the substitutions, we successfully engineered a protein A variant that exhibited high pH sensitivity and maintained affinity, thermal stability, and alkaline tolerance. The variant was capable of serving as an affinity ligand that made affinity chromatography under milder acidic conditions possible; the elution peak shifted from pH 4.2 to 5.6. Only two substitutions were needed to achieve this pH sensitivity. This structure-based approach is applicable to other protein-based ligands.
Journal of chromatography. B, Analytical technologies in the biomedical and life sciences 04/2013; 929C:155-160. · 2.78 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Protein-protein interaction in response to environmental conditions enables sophisticated biological and biotechnological processes. Aiming toward the rational design of a pH-sensitive protein-protein interaction, we engineered pH-sensitive mutants of streptococcal protein G B1, a binder to the IgG constant region. We systematically introduced histidine residues into the binding interface to cause electrostatic repulsion on the basis of a rigid body model. Exquisite pH sensitivity of this interaction was confirmed by surface plasmon resonance and affinity chromatography employing a clinically used human IgG. The pH-sensitive mechanism of the interaction was analyzed and evaluated from kinetic, thermodynamic, and structural viewpoints. Histidine-mediated electrostatic repulsion resulted in significant loss of exothermic heat of the binding that decreased the affinity only at acidic conditions, thereby improving the pH sensitivity. The reduced binding energy was partly recovered by "enthalpy-entropy compensation." Crystal structures of the designed mutants confirmed the validity of the rigid body model on which the effective electrostatic repulsion was based. Moreover, our data suggested that the entropy gain involved exclusion of water molecules solvated in a space formed by the introduced histidine and adjacent tryptophan residue. Our findings concerning the mechanism of histidine-introduced interactions will provide a guideline for the rational design of pH-sensitive protein-protein recognition.
Journal of Biological Chemistry 04/2009; 284(18):12373-83. · 4.65 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: What is the smallest protein? This is actually not such a simple question to answer, because there is no established consensus among scientists as to the definition of a protein. We describe here a designed molecule consisting of only 10 amino acids. Despite its small size, its essential characteristics, revealed by its crystal structure, solution structure, thermal stability, free energy surface, and folding pathway network, are consistent with the properties of natural proteins. The existence of this kind of molecule deepens our understanding of proteins and impels us to define an "ideal protein" without inquiring whether the molecule actually occurs in nature.
Journal of the American Chemical Society 11/2008; 130(46):15327-31. · 10.68 Impact Factor