Pathogenic bacteria remodel central metabolic enzyme to build a cyclopropanol warhead

Area of Science:

• Microbiology
• Biochemistry
• Structural Biology

Background:

• The Burkholderia pseudomallei (BP) group causes serious infectious diseases like melioidosis and glanders.
• BP bacteria possess a gene cluster for synthesizing polyketides (malleicyprols) with a virulence-critical cyclopropanol unit.
• The biochemical pathway for cyclopropanol formation and the enzymes involved remain largely unknown.

Purpose of the Study:

• To elucidate the biochemical mechanism of malleicyprol warhead formation in Burkholderia pseudomallei.
• To identify and characterize the enzyme responsible for constructing the cyclopropanol ring.
• To provide structural insights into the enzyme's catalytic mechanism.

Main Methods:

• Biochemical assays were employed to study enzyme activity.
• X-ray crystallography was used to determine the structures of the enzyme (BurG) in various states.
• Mutagenesis studies were performed on key enzyme residues.

Main Results:

• The enzyme BurG, an NAD+-dependent ketol-acid reductoisomerase family member, was identified as the cyclopropanol-forming enzyme.
• Eight crystal structures revealed the enzyme's mechanism, including a hidden oxidoreduction and C-S bond cleavage.
• Structural and biochemical data elucidated the step-by-step formation of the strained cyclopropanol ring.

Conclusions:

• BurG catalyzes the formation of the malleicyprol warhead through a novel mechanism.
• This study reveals a unique instance of enzyme neofunctionalization, repurposing a central metabolism enzyme for virulence factor production.
• Understanding this pathway opens opportunities for targeted antivirulence drug development against BP infections.