Kanglemycin A Can Overcome Rifamycin Resistance Caused by ADP-Ribosylation by Arr Protein

Area of Science:

• Microbiology
• Molecular Biology
• Drug Discovery

Background:

• Rifamycins are crucial antibiotics targeting bacterial RNA polymerase (RNAP).
• Resistance often arises from RNAP mutations, but some bacteria employ ADP-ribosyl transferases (Arr) to inactivate rifamycins.
• Arr enzymes modify rifamycins via ADP-ribosylation, rendering them ineffective.

Purpose of the Study:

• To investigate how ADP-ribosylation by Arr affects rifampicin's inhibition of transcription.
• To determine if kanglemycin A (KglA), a natural rifamycin, is susceptible to Arr-mediated inactivation.
• To explore the structural basis for differential inactivation of rifamycins by Arr enzymes from different bacterial species.

Main Methods:

• Biochemical assays to measure transcription inhibition by rifampicin and KglA.
• Enzymatic assays using purified Arr enzymes from *Mycobacterium smegmatis* and *Mycobacterium abscessus*.
• Structural analysis and comparison of Arr enzyme active sites.

Main Results:

• ADP-ribosylation by Arr directly abolishes rifampicin's ability to inhibit transcription.
• Kanglemycin A, due to its unique sugar moiety, is not inactivated by *M. smegmatis* Arr.
• However, KglA is inactivated by *M. abscessus* Arr, suggesting evolutionary adaptation.
• Differences in Arr enzyme structure, specifically at the interaction site with KglA's sugar moiety, explain the differential inactivation.

Conclusions:

• ADP-ribosylation is a key mechanism for bacterial resistance to rifampicin.
• Kanglemycin A exhibits resistance to certain Arr enzymes, highlighting its potential as an antimicrobial.
• Structural variations in Arr enzymes contribute to the evolution of resistance and susceptibility to different rifamycins.