Affinity-matured antibody with a disulfide bond in H-CDR3 loop.

Affinity maturation increases antigen-binding affinity and specificity of antibodies by somatic hypermutation. Various monoclonal antibodies against (4-hydroxy-3-nitrophenyl)acetyl (NP) were obtained during affinity maturation. Among them, highly matured anti-NP antibodies, such as E11 and E3, possess Cys96 and Cys100 in the complementarity-determining region 3 of the heavy chain, which would form a disulfide bond.

Metal-binding and folding thermodynamics of Escherichia coli ribonuclease HI related to its catalytic function.

Escherichia coli ribonuclease HI (RNH) hydrolyzes the RNA strands of RNA/DNA hybrids in the presence of Mg at the highest level, relative to other metal ions. The Mg binding affinity was 8.39 × 10 M, which was lower than those of other metal ions.

Pivotal role of a conserved histidine in Escherichia coli ribonuclease HI as proposed by X-ray crystallography.

The ribonuclease (RNase) H family of enzymes catalyze the specific cleavage of RNA strands of RNA/DNA hybrid duplexes and play an important role in DNA replication and repair. Since the first report of the crystal structure of RNase HI, its catalytic mechanisms, which require metal ions, have been discussed based on numerous structural and functional analyses, including X-ray crystallography. In contrast, the function of the conserved histidine residue (His124 in Escherichia coli) in the flexible loop around the active site remains poorly understood, although an important role was suggested by NMR analyses.