Affitin

Affitins, also known as AdNectin proteins, are a class of non-antibody scaffold proteins engineered for high-affinity binding to specific target molecules. Unlike antibodies, which are based on immunoglobulin domains, affitins are derived from the Saccharomyces cerevisiae protein Sac7d, a small, highly stable DNA-binding protein.

Affitins are significantly smaller than antibodies (around 6 kDa compared to 150 kDa for IgG antibodies), which can offer advantages in tissue penetration and biodistribution. They are typically selected and optimized using combinatorial library display technologies, such as phage display or ribosome display, to identify variants with high affinity for the desired target.

Key characteristics of affitins include:

• Non-immunoglobulin scaffold: They are not derived from the immune system and, therefore, generally exhibit lower immunogenicity compared to antibodies.
• Small size: This allows for better tissue penetration and faster clearance from the body.
• High stability: Affitins are known for their resistance to heat, pH extremes, and proteases.
• Ease of production: They can be efficiently produced in microbial systems like E. coli, making them cost-effective to manufacture.
• Versatility: Affitins can be engineered to bind a wide range of targets, including proteins, peptides, small molecules, and even nucleic acids.
• Modular design: Functional domains, such as fluorescent tags or cytotoxic payloads, can be readily fused to affitins to create multifunctional molecules for various applications.

Affitins are being explored for a variety of applications, including:

• Diagnostics: As targeting agents for medical imaging and biosensors.
• Therapeutics: As drug delivery vehicles and targeted therapies for cancer and other diseases.
• Biotechnology: As affinity reagents for protein purification, enzyme immobilization, and other applications.
• Research: As tools for studying protein-protein interactions and other biological processes.

Their unique properties and versatile design make affitins a promising alternative to antibodies in many areas of research and development.