Transglutaminase-mediated internal protein labeling with a designed peptide loop.

Area of Science:

• Biochemistry
• Protein Engineering
• Enzymology

Background:

• Post-translational modification is crucial for protein function.
• Site-specific protein labeling enables precise functional studies.
• Microbial transglutaminase (MTG) offers a tool for targeted protein modification.

Purpose of the Study:

• To investigate post-translational internal protein labeling via a genetically encoded peptide tag.
• To assess the impact of site-specific labeling on enzyme activity.
• To develop a method for labeling proteins without functional impairment.

Main Methods:

• Insertion of a 13-mer peptidyl loop (K-loop) containing a lysine residue into bacterial alkaline phosphatase (BAP).
• Enzymatic labeling of the K-loop using microbial transglutaminase (MTG) and a Gln-donor substrate.
• Assay of BAP activity following site-specific labeling at different protein locations.

Main Results:

• Successful MTG-mediated labeling of the engineered K-loop within BAP.
• Labeling near the BAP active site (residues 91-93) significantly reduced enzyme activity.
• Labeling at a distal site (residues 219-221) allowed site-specific covalent modification without affecting BAP activity.

Conclusions:

• Genetically encoded peptide tags can facilitate site-specific post-translational protein labeling.
• The location of labeling is critical for maintaining protein function.
• This method provides a strategy for internal protein modification without compromising enzymatic activity.