Ralstonia eutropha TF93 is blocked in tat-mediated protein export

Area of Science:

• Microbiology
• Protein Transport
• Enzyme Biochemistry

Background:

• Ralstonia eutropha TF93 is a bacterium known for its metabolic versatility.
• Proper translocation of redox enzymes is crucial for bacterial respiration and energy metabolism.
• The twin-arginine translocation (Tat) system is responsible for exporting folded proteins across membranes.

Purpose of the Study:

• To investigate the role of the twin-arginine signal peptide in the translocation of redox enzymes in Ralstonia eutropha TF93.
• To identify the specific redox enzymes affected by translocation defects in strain TF93.
• To determine if the TatA protein can restore normal enzyme localization.

Main Methods:

• Immunoblot analysis to detect protein localization.
• Physiological studies to assess enzyme activity and function.
• Heterologous expression of Azotobacter chroococcum tatA in Ralstonia eutropha TF93.

Main Results:

• The catalytic subunits of membrane-bound [NiFe] hydrogenase (MBH) and periplasmic nitrate reductase (Nap) were mislocalized in TF93.
• Copper-containing nitrous oxide reductase (NosZ) also failed to translocate to the periplasm.
• Enzymatic activity of translocated MBH and Nap suggested cofactor insertion prior to export.
• Heterologous expression of TatA restored the periplasmic destination of MBH, Nap, and NosZ.

Conclusions:

• Ralstonia eutropha TF93 has a defect in the twin-arginine signal peptide-dependent protein translocation pathway.
• This defect affects the localization of essential redox enzymes involved in respiration.
• The bacterial TatA protein is essential for the proper export of these enzymes and can restore function when expressed heterologously.