The lon protease from Mycobacterium smegmatis: molecular cloning, sequence analysis, functional expression, and...

Area of Science:

• Microbiology
• Molecular Biology
• Biochemistry

Background:

• Mycobacterium smegmatis possesses a Lon homolog (Ms-Lon), an ATP-dependent protease.
• This finding, combined with previous research, establishes M. smegmatis as the first known eubacterium with both Lon and a complete 20S proteasome.

Purpose of the Study:

• To characterize the M. smegmatis Lon homolog (Ms-Lon).
• To investigate the functional conservation and substrate specificity of Ms-Lon compared to E. coli Lon (Ec-Lon).
• To explore the catalytic activity and structural interactions within Ms-Lon.

Main Methods:

• Gene characterization of M. smegmatis Lon homolog.
• Functional expression and toxicity assays in E. coli.
• In vitro peptidase activity assays with purified Ms-Lon.
• Site-directed mutagenesis of the catalytic residue (S675) and ATPase activity assays.

Main Results:

• Ms-Lon expression in E. coli showed moderate toxicity, indicating conserved discrimination against non-substrate proteins.
• Ms-Lon efficiently degraded RcsA, a known substrate of Ec-Lon, demonstrating conserved substrate recognition.
• Purified Ms-Lon exhibited chymotrypsin-like specificity, requiring ATP/dATP and stimulated by unfolded protein.
• Mutagenesis of S675 significantly reduced in vitro activity, but the S675C variant retained specific in vivo protease activity.
• Ms-Lon variants showed reduced ATPase activity, suggesting interaction between active sites.

Conclusions:

• M. smegmatis Lon homolog (Ms-Lon) shares functional and substrate specificity conservation with E. coli Lon.
• Ms-Lon possesses distinct catalytic properties and active site interactions.
• The study highlights the conserved nature of protein degradation machinery in eubacteria.