Linker modification introduces useful molecular instability in a single chain antibody

Area of Science:

• Biochemistry
• Molecular Biology
• Immunotechnology

Background:

• Recombinant single-chain antibodies (SCAs) are engineered proteins combining variable light (VL) and variable heavy (VH) domains.
• SCAs can be designed to bind specific targets, such as fluorescein (Fl), and modulate their properties, like fluorescence.
• Understanding SCA stability is crucial for their application in analytical systems and biosensors.

Purpose of the Study:

• To investigate the denaturation process of a fluorescein-binding SCA (SCA 4-4-20/212).
• To construct and characterize a novel SCA (SCA 4-4-20/9) with a modified linker length.
• To compare the binding, stability, and proteolysis susceptibility of SCAs with different linker lengths.

Main Methods:

• Site-directed mutagenesis using PCR to create SCA 4-4-20/9 with a nine-residue linker from SCA 4-4-20/212 (14-residue linker).
• Fluorescence quenching assay to monitor binding of SCAs to fluorescein (Fl).
• Assessment of antibody denaturation, heat stability, response to denaturing agents, and susceptibility to proteolysis.

Main Results:

• SCA 4-4-20/212 binding to Fl quenched fluorescence, allowing monitoring of antibody denaturation in a two-step process (rapid then slow).
• The two-step denaturation suggests selective susceptibility of CDR loops.
• SCA 4-4-20/9, with a shorter linker, exhibited increased sensitivity to denaturation and proteolysis compared to SCA 4-4-20/212, indicating a conformational rearrangement.

Conclusions:

• The linker length significantly impacts the conformational stability and susceptibility to degradation of recombinant single-chain antibodies.
• The modified SCA 4-4-20/9 demonstrates increased molecular instability, which could be advantageous for specific applications.
• Engineered molecular instability in SCAs may be a valuable feature for their use in analytical systems and biosensor development.