Expressed Protein Ligation without Intein.

Area of Science:

• Biochemistry
• Chemical Biology
• Synthetic Biology

Background:

• Functionalized C-termini, like C-terminal thioesters, are crucial for synthesizing larger proteins using expressed protein ligation.
• Current methods often rely on intein fusion, which can lead to premature hydrolysis and poor compatibility with denatured conditions.

Purpose of the Study:

• To develop an enzyme-free method for expressed protein ligation.
• To bypass the limitations of traditional intein-based protein ligation techniques.

Main Methods:

• Chemically activating a cysteine residue in a recombinant protein using a cyanylating reagent.
• Utilizing the activated cysteine's N-side amide for nucleophilic acyl substitution with various amines, including amino acids and hydrazine.
• Generating protein hydrazides for subsequent expressed protein ligation.

Main Results:

• Demonstrated the successful synthesis of complex protein conjugates, including ubiquitin and ubiquitin-like protein conjugates.
• Synthesized modified histone H2A with C-terminal posttranslational modifications and active RNase H.
• Produced exenatide, a commercially available therapeutic peptide, showcasing the method's versatility.
• Achieved protein ligation without enzymatic intervention, overcoming issues like premature hydrolysis.

Conclusions:

• Activated Cysteine-Directed Protein Ligation (ACPL) offers a simple yet powerful enzyme-free alternative for protein synthesis.
• This technique significantly expands the synthetic capabilities in protein chemistry.
• ACPL opens new avenues for research in protein modification and bioconjugation.