Structure of 2-keto-3-deoxy-6-phosphogluconate (KDPG) aldolase from Pseudomonas putida

Area of Science:

• Biochemistry
• Structural Biology
• Enzymology

Background:

• The Entner-Doudoroff pathway is crucial for bacterial carbohydrate metabolism.
• 2-Keto-3-deoxy-6-phosphogluconate (KDPG) aldolase catalyzes a key cleavage step in this pathway.
• Understanding enzyme structure-function relationships is vital for metabolic pathway analysis.

Purpose of the Study:

• To determine the high-resolution crystal structure of KDPG aldolase from Pseudomonas putida.
• To elucidate the structural basis of the Schiff-base mechanism employed by the enzyme.
• To compare the structure with homologous enzymes and understand evolutionary conservation.

Main Methods:

• X-ray crystallography was used to refine the enzyme's structure to a resolution of R = 17.1% (R(free) = 21.4%).
• Structural analysis focused on the active site, subunit interactions, and overall fold.
• Comparative structural analysis was performed against the KDPG aldolase from Escherichia coli.

Main Results:

• The refined crystal structure reveals an (betaalpha)(8)-barrel fold with the active site located on the C-terminal side.
• The catalytic residue Lys145 is identified and shown to be coordinated by a sulfate/phosphate ion and water molecules.
• The enzyme forms a trimer stabilized by hydrophobic interactions, with specific inter-subunit hydrogen bonds noted.
• The overall structure closely mirrors that of the homologous enzyme from Escherichia coli, except for the N-terminal helix.

Conclusions:

• The crystal structure provides a detailed molecular model of KDPG aldolase from P. putida.
• Structural insights support a class I Schiff-base mechanism for KDPG cleavage.
• The high degree of structural similarity to the E. coli enzyme suggests conserved functional and evolutionary properties.