Poly(3-hydroxybutyrate) depolymerases bind to their substrate by a C-terminal located substrate binding site

Area of Science:

• Biochemistry
• Microbiology
• Polymer Science

Background:

• Poly(3-hydroxybutyrate) (PHB) is a biodegradable polymer produced by various microorganisms.
• PHB depolymerases are enzymes responsible for the degradation of PHB.
• Understanding the substrate-binding mechanism of PHB depolymerases is crucial for their biotechnological applications.

Purpose of the Study:

• To investigate the substrate specificity of PHB depolymerase binding.
• To identify the specific domains within PHB depolymerases responsible for binding to PHB granules.
• To compare the binding affinities of wild-type and truncated PHB depolymerases to different polymeric substrates.

Main Methods:

• Purification of wild-type and truncated PHB depolymerase PhaZ4 from Pseudomonas lemoignei.
• Incubation of purified proteins with aqueous suspensions of PHB, chitin, and cellulose.
• Analysis of protein binding to polymeric substrates using biochemical assays.

Main Results:

• Wild-type PHB depolymerase PhaZ4 specifically bound to PHB granules.
• A truncated form of PhaZ4, lacking C-terminal amino acids, showed reduced or no binding to PHB.
• No significant binding was observed between other tested proteins (lactate dehydrogenase) and polymeric substrates (chitin, cellulose).

Conclusions:

• The C-terminal amino acids of PHB depolymerases are essential for specific binding to PHB.
• These C-terminal regions constitute a PHB-specific binding domain or a critical part thereof.
• This finding has implications for engineering PHB depolymerases with enhanced activity and specificity.