Structural basis of poly(3-hydroxybutyrate) hydrolysis by PhaZ7 depolymerase from Paucimonas lemoignei.

Area of Science:

• Biochemistry
• Structural Biology
• Enzymology

Background:

• Poly(3-hydroxybutyrate) (PHB) is a biodegradable polymer with significant industrial applications.
• PHB depolymerases are enzymes crucial for PHB degradation and recycling.
• Understanding the structure of PHB depolymerases provides insights into their catalytic mechanisms and substrate specificity.

Purpose of the Study:

• To determine the crystal structure of poly(3-hydroxybutyrate) (PHB) depolymerase PhaZ7 from Paucimonas lemoignei.
• To compare the structure of PhaZ7 with other known PHB depolymerases and related enzymes.
• To elucidate the structural basis for substrate binding and catalytic activity of PhaZ7.

Main Methods:

• X-ray crystallography was used to determine the crystal structure of PhaZ7 at 1.90 A resolution.
• Structural comparisons were performed using the Protein Data Bank (PDB).
• Analysis of active site residues and solvent-exposed residues involved in substrate binding.

Main Results:

• The crystal structure of PhaZ7 revealed a single domain with an alpha/beta hydrolase fold.
• The active site contains a catalytic triad (Ser136, Asp242, His306), characteristic of serine esterases/lipases.
• PhaZ7 shares structural similarity with Bacillus subtilis lipase LipA but differs significantly from Penicillium funiculosum PHB depolymerase.
• PhaZ7 utilizes aromatic residues for substrate binding, and its active site is buried, requiring conformational changes for substrate access, unlike P. funiculosum PHB depolymerase.

Conclusions:

• PhaZ7 and P. funiculosum PHB depolymerase employ distinct strategies for substrate binding due to differences in active site accessibility and residue usage.
• The structural data suggest that PhaZ7's buried active site and specific residue interactions contribute to its substrate specificity.
• Further conformational changes are necessary for PhaZ7 to access its polymeric substrate, highlighting unique enzymatic adaptations.