High-resolution 2D solid-state NMR provides insights into nontuberculous mycobacteria

Area of Science:

• Biophysical Chemistry
• Microbiology
• Structural Biology

Background:

• Nontuberculous mycobacteria (NTM) are a growing public health concern, with some species posing significant pathogenic threats.
• Understanding the structural and chemical differences in NTM cell walls is crucial for developing targeted treatments.
• Previous characterization methods have limitations in resolving the complex composition of mycobacterial cell envelopes.

Purpose of the Study:

• To employ high-resolution magic-angle spinning (MAS) solid-state NMR (ssNMR) for detailed characterization of NTM cell-wall components.
• To compare the cell-wall composition and dynamics between a model NTM strain (Mycobacterium smegmatis) and a pathogenic strain (Mycobacterium abscessus).
• To identify specific chemical sites and molecular structures within the NTM cell envelope using advanced NMR techniques.

Main Methods:

• Utilized 1D and 2D 1H-13C ssNMR spectroscopy on hydrated, whole-cell, and isolated cell envelope NTM samples.
• Employed cross-polarization (CP) andinsensitive nuclei enhancement (INEPT) based NMR pulse sequences for selective signal analysis.
• Applied peak deconvolution and chemical shift analysis to assign signals to specific cell-wall components, complemented by electron microscopy (EM).

Main Results:

• Identified over 100 distinct 13C signals, with tentative assignments for approximately 30 polysaccharides.
• Detected signals corresponding to peptidoglycan, arabinogalactan, and mycolic acid in both NTM strains.
• Observed differences suggesting a smaller, more flexible peptidoglycan layer in M. abscessus compared to M. smegmatis, potentially linked to pathogenicity.

Conclusions:

• High-resolution 2D ssNMR is a powerful tool for first-time characterization and chemical site identification in NTM strains.
• Distinct cell-wall structural features, particularly in the peptidoglycan layer, may correlate with the pathogenicity of NTM species.
• These findings provide a foundation for developing structure-based strategies to combat NTM infections.