Cyclic Peptide Antibody Purification Ligand

The patent extracts only the essential binding function from protein A by designing a minimal cyclic peptide sequence (Formula I) that retains IgG binding capability while removing the bacterial protein structure responsible for immunogenicity and endotoxin contamination. The cyclic peptide consists of 13-17 amino acid residues with specific structural features that enable selective antibody binding without the harmful properties of full-length protein A.

The patent creates a simplified copy or model of protein A's binding interface through the cyclic peptide structure. Instead of using the complete protein A molecule, the invention synthesizes a peptide copy that mimics the critical binding region, achieving the same purification function with reduced complexity and eliminated harmful components.

The patent employs a cost-effective synthetic peptide approach rather than expensive protein purification processes. The cyclic peptide can be synthesized through standard peptide synthesis methods, which are more economical than producing and highly purifying bacterial protein A. This disposable synthetic ligand approach reduces both manufacturing cost and immunogenicity simultaneously.

The patent changes the fundamental parameter of the affinity ligand from a large bacterial protein to a small synthetic peptide. This parameter change in molecular size, origin, and structure enables achieving low immunogenicity through synthesis rather than through expensive purification processes, thereby reducing overall manufacturing cost.

The patent applies local quality by forming a cyclic structure at the critical binding region while maintaining flexibility in other parts of the peptide. The cyclic portion (formed by disulfide bond or other crosslinks) provides chemical stability where needed, while the linear portions maintain conformational flexibility for optimal antibody binding, thus resolving the contradiction between stability and activity.

The patent creates a composite structure combining cyclic and linear segments within the same peptide. The cyclic portion provides structural stability and chemical resistance, while the linear extensions maintain binding flexibility. This composite architecture allows simultaneous achievement of both chemical resistance and binding activity.