Affinity maturation of a V(H)H by mutational hotspot randomization.

Area of Science:

• Biotechnology
• Immunology
• Protein Engineering

Background:

• V(H)H antibodies from naive libraries typically exhibit low micromolar dissociation constants (K(D)s), necessitating affinity improvement for therapeutic and diagnostic applications.
• Current affinity maturation methods include non-targeted in vitro approaches with significant affinity gains, alongside a targeted strategy using specific nucleotide mutational hotspots.

Purpose of the Study:

• To improve the affinity of a parathyroid hormone (PTH)-specific V(H)H antibody (PTH22) using targeted randomization of hotspot codons.
• To investigate the role of these hotspot codons in antibody affinity, solubility, and structural integrity.

Main Methods:

• Construction of a PTH22 mutant ribosome display library by randomizing nine complementarity-determining region (CDR) hotspot codons (AGY/RGYW).
• Affinity assessment of the resulting V(H)H variants.
• Nucleotide sequence analysis of wild-type and evolved V(H)Hs to understand mutational patterns.

Main Results:

• A lead V(H)H binder with a 30-fold affinity improvement was identified.
• Sequence analysis indicated that many AGY/RGYW hotspots are not primarily linked to affinity enhancement.
• These hotspots appear to influence V(H)H solubility, structural stability, and deletion/insertion events.

Conclusions:

• Targeted hotspot codon mutagenesis can achieve moderate affinity increases in V(H)H antibodies.
• This mutagenesis strategy is valuable for simultaneously optimizing antibody physical properties, such as solubility and structure, alongside affinity.
• The findings suggest a more nuanced role for specific nucleotide hotspots in V(H)H antibody engineering than previously assumed.