A distinct holoenzyme organization for two-subunit pyruvate carboxylase

Area of Science:

• Biochemistry
• Structural Biology
• Microbiology

Background:

• Pyruvate carboxylase (PC) is vital for metabolism and bacterial virulence.
• PC typically exists as a homo-tetramer or a two-subunit enzyme with proposed α4β4 stoichiometry.
• Understanding PC structure is key to its function in bacteria.

Purpose of the Study:

• To determine the crystal structure of the two-subunit pyruvate carboxylase from Methylobacillus flagellatus.
• To elucidate the holoenzyme stoichiometry and architecture of this bacterial PC.
• To investigate the role of two-subunit PC in bacterial physiology.

Main Methods:

• X-ray crystallography to determine the three-dimensional structure of M. flagellatus PC.
• Biochemical assays to confirm enzyme stoichiometry.
• Mutagenesis studies to validate structural findings.
• Functional studies in Pseudomonas aeruginosa to assess PC's role in colony morphogenesis.

Main Results:

• The crystal structures revealed an unexpected α2β4 stoichiometry for the M. flagellatus PC holoenzyme.
• The overall architecture of the α2β4 holoenzyme is distinct from homo-tetrameric PCs.
• Biochemical and mutagenesis data confirmed the α2β4 stoichiometry.
• Functional studies demonstrated that two-subunit PC is essential for colony morphogenesis in Pseudomonas aeruginosa.

Conclusions:

• The study reveals a novel α2β4 stoichiometry for a two-subunit pyruvate carboxylase, challenging previous assumptions.
• The unique structural architecture of this PC holoenzyme provides new insights into its function.
• Two-subunit PC plays a significant role in bacterial colony development, highlighting its importance beyond basic metabolism.