6 research outputs found
Crystal Structure of a Ten-Amino Acid Protein
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
Crystal Structure of a Ten-Amino Acid Protein
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
Optimizing pH Response of Affinity between Protein G and IgG Fc: HOW ELECTROSTATIC MODULATIONS AFFECT PROTEIN-PROTEIN INTERACTIONS*S⃞
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