Crystalline-structure-dependent enzymatic degradation of polymorphic poly(3-hydroxypropionate)

Area of Science:

• Polymer Science
• Biochemistry
• Materials Science

Background:

• Polymorphic poly(3-hydroxypropionate) (P3HP) shares a backbone with bacterial poly(3-hydroxyalkanoate)s (P3HAs).
• Previous studies suggested P3HA enzymatic degradation correlates with crystallinity and lamellar thickness.

Purpose of the Study:

• To investigate the influence of crystalline structure on the enzymatic degradation of polymorphic P3HP.
• To elucidate the relationship between P3HP crystal forms and their susceptibility to enzymatic breakdown.

Main Methods:

• Differential scanning calorimetry for thermal properties.
• Wide-angle X-ray diffraction and small-angle X-ray scattering for crystalline structure and morphology.
• Carbon-13 solid-state NMR spectroscopy for molecular dynamics.
• Enzymatic degradation assays using P3HA depolymerase from Ralstonia pickettii T1.

Main Results:

• Crystallinity and lamellar thickness decreased in the order: beta-form > gamma-form > delta-form.
• Contrary to expectations, enzymatic degradation rates increased in the order: delta-form < gamma-form < beta-form.
• The beta-form degraded nearly one order of magnitude faster than the delta-form.

Conclusions:

• P3HP crystalline structure decisively dictates its enzymatic degradation rate.
• Degradation rate is minimized when P3HP adopts a 2_1 helix conformation, similar to poly(3-hydroxybutyrate) (P3HB).
• Molecular interactions and dynamics within polymorphic P3HP crystals explain this unique degradation behavior.