Mycobacterium tuberculosis assembles a unique hexameric E2p core of the pyruvate dehydrogenase complex

Area of Science:

• Biochemistry
• Structural Biology
• Microbiology

Background:

• The pyruvate dehydrogenase complex (PDHc) is crucial for cellular metabolism, converting pyruvate to acetyl-CoA.
• PDHc's core scaffold, dihydrolipoyl transacetylase (E2p), typically forms 24-mer or 60-mer structures.
• Mycobacterium tuberculosis (Mtb) E2p (DlaT) also functions in a peroxynitrite reductase/peroxidase (PNR/P) complex.

Purpose of the Study:

• To determine the assembly and structure of the Mtb E2p core (DlaT).
• To investigate the functional implications of the Mtb PDHc architecture.
• To understand how Mtb PDHc architecture relates to its dual role in metabolism and antioxidant defense.

Main Methods:

• Cryo-electron microscopy (cryo-EM) to determine the structure of DlaT assemblies.
• Structure-guided mutagenesis to probe protein interfaces.
• In vitro activity assays to assess PDHc function.

Main Results:

• DlaT assembles into hexamers and dodecamers at physiologically relevant concentrations.
• The hexameric form of DlaT functions as the E2p core of the Mtb PDHc.
• Unique inter-trimer interfaces prevent the formation of canonical 24- or 60-mer structures.

Conclusions:

• Mtb PDHc exhibits a noncanonical hexameric E2p core, distinct from other characterized PDHcs.
• This specialized architecture facilitates metabolic regulation and adaptation to oxidative stress via the PNR/P pathway.
• The findings reveal novel diversity in PDHc organization and a unique metabolic complex structure in mycobacteria.