Structural basis for microcin C7 inactivation by the MccE acetyltransferase

Area of Science:

• Microbiology
• Structural Biology
• Biochemistry

Background:

• Microcin C7 (McC) is a bacteriocin that inhibits protein synthesis by targeting aspartyl-tRNA synthetase.
• McC is produced as a conjugate and activated by processing, posing a self-toxicity risk to producing strains.
• The mccE gene product, MccE, inactivates processed McC via acetylation, contributing to bacterial autoimmunity.

Purpose of the Study:

• To characterize the acetylation mechanism of processed microcin C7 by the MccE enzyme.
• To elucidate the structural basis of MccE's substrate recognition and acetylation activity.

Main Methods:

• Biochemical assays to study the MccE acetyltransferase domain (MccE(AcTase)) activity.
• X-ray crystallography to determine the structures of MccE(AcTase) in complex with substrates, inhibitors, and products.
• Analysis of protein-ligand interactions, including π-stacking interactions.

Main Results:

• Detailed characterization of the MccE(AcTase) enzymatic mechanism.
• Determination of five crystal structures providing insights into substrate binding.
• Identification of an unexpected substrate recognition mode involving π-stacking interactions.
• Demonstration that MccE(AcTase) can detoxify various aminoacylnucleotides beyond microcin C7.

Conclusions:

• The MccE enzyme utilizes a unique π-stacking interaction for substrate recognition, similar to cap-binding proteins.
• Structural insights explain MccE's broad substrate specificity in detoxifying aminoacylnucleotides.
• This study provides a molecular understanding of antibiotic self-immunity mechanisms in bacteria.