A method for parallel microscale protein labeling and precise control over the average degree of labeling (aDoL)

Area of Science:

• Bioconjugation Chemistry
• Protein Engineering
• Chemical Biology

Background:

• Traditional protein conjugation via lysine residues and active esters faces challenges in controlling the degree of labeling (DoL).
• Instability of active esters and variable reaction efficiencies limit precise control in standard labeling methods.

Purpose of the Study:

• To develop a robust protocol for precise control of protein labeling degree (DoL) using Copper-free Click Chemistry.
• To offer a simplified, economical, and efficient method for parallel microscale protein labeling.

Main Methods:

• A two-step reaction protocol involving initial protein activation with azide-NHS (N-Hydroxysuccinimide).
• Subsequent reaction of the azide-activated protein with a limited amount of a complementary click tag.
• Purification after the first step to remove unreacted reagents before the click reaction.

Main Results:

• The click tag fully reacts with the azide-activated protein within 24 hours, eliminating the need for post-reaction purification.
• The achieved DoL directly corresponds to the input molar ratio of the click tag to the protein.
• Demonstrated parallel microscale labeling of an antibody with 9 different fluorophores using 0.5 mg of antibody.
• Achieved targeted DoL values ranging from 2 to 8 for antibody labeling.
• Conjugated fluorophores exhibited enhanced stability compared to those labeled using standard NHS-fluorophore methods.

Conclusions:

• The developed Copper-free Click Chemistry protocol provides superior control over protein labeling degree (DoL).
• This method simplifies and reduces the cost of parallel microscale protein labeling.
• The click chemistry approach results in more stable protein-conjugate linkages compared to traditional methods.