Developing crosslinkers specific for epimerization domain in NRPS initiation modules to evaluate mechanism.

Area of Science:

• Biochemistry
• Enzymology
• Natural Product Biosynthesis

Background:

• Nonribosomal peptide synthetases (NRPSs) are crucial for synthesizing complex peptides, including those with d-amino acids.
• The epimerization (E) domain within NRPSs catalyzes the stereochemical conversion of l-amino acids to d-amino acids, a vital step in natural product formation.
• The precise catalytic mechanism of E domains remains incompletely understood.

Purpose of the Study:

• To develop novel chemical tools for elucidating the catalytic mechanism and identifying key residues of NRPS epimerization (E) domains.
• To investigate the specific roles of catalytic residues in the l- to d-amino acid conversion mediated by the E domain.

Main Methods:

• Design and synthesis of pantetheine crosslinking probes mimicking the natural substrate l-Phe.
• Application of mechanism-based crosslinking assays coupled with MALDI-TOF Mass Spectrometry (MS) to identify crosslinking sites.
• Site-directed mutagenesis to validate the identified catalytic residues and compare their reactivity.

Main Results:

• Identification of histidine (H743) and glutamate (E882) as critical crosslinking site residues within the E domain.
• Mutagenesis studies confirmed the catalytic roles of H743 and E882.
• Glutamate (E882) was identified as the dominant nucleophile, supporting its role in deprotonating the Cα-H of amino acid substrates.

Conclusions:

• Pantetheine crosslinking probes are effective tools for studying the molecular mechanisms of E domains and potentially C domains.
• The findings provide critical insights into the catalytic machinery of E domains, specifically highlighting the roles of histidine and glutamate.
• This research advances the understanding of NRPS function, aiding efforts in combinatorial biosynthesis for novel compound discovery.