Identification of substrates of the Mycobacterium tuberculosis proteasome

Area of Science:

• Microbiology
• Molecular Biology
• Biochemistry

Background:

• Mycobacterium tuberculosis (Mtb) proteasome-associated proteins Mpa (Mycobacterium proteasomal ATPase) and PafA (proteasome accessory factor A) are vital for virulence and nitric oxide resistance.
• A direct functional link between the Mtb proteasome protease and Mpa/PafA, and in vitro protein degradation by bacterial proteasomes, has not been previously established.

Purpose of the Study:

• To identify the first natural substrates of the bacterial proteasome.
• To elucidate the roles of Mpa and PafA in regulating the levels of essential enzymes involved in Mtb pathogenesis.
• To investigate the functional importance of Mpa in proteasome-dependent protein degradation.

Main Methods:

• Identification of proteasome substrates using biochemical assays.
• Enzyme activity assays to assess the role of Mpa and PafA in regulating substrate levels.
• Site-directed mutagenesis to investigate the function of conserved residues in Mpa.

Main Results:

• Malonyl Co-A acyl carrier protein transacylase and ketopantoate hydroxymethyltransferase were identified as the first bacterial proteasome substrates.
• Mpa and PafA, along with proteasome protease activity, are necessary for maintaining physiological levels of these identified substrates.
• Mpa levels are regulated in a proteasome-dependent manner, and a conserved tyrosine residue in Mpa is essential for its function.

Conclusions:

• The Mtb proteasome, with Mpa and PafA, degrades key bacterial proteins essential for virulence.
• These findings provide the first evidence of in vitro protein degradation by bacterial proteasomes and highlight their role in regulating virulence factors.