Disordered N-termini enhance the thermostability of SGNH-hydrolase family polyesterases.

Polyesters are widely used plastics that persist in the environment due to their resistance to degradation. Microbial polyesterases potentially offer recycling and remediation solutions. However, most polyesterases lack the thermostability and catalytic efficiency required for practical application. Here, we have identified and characterized thermostable bacterial polyesterases from an undercharacterized subfamily of SGNH-hydrolases (related to PpEST from Pseudomonas oleovorans) and uncovered a previously unreported thermal stabilization mechanism mediated by conformationally flexible N-terminal regions with features of intrinsically disordered regions. Biochemical assays, structural analysis, small angle X-ray scattering, X-ray crystallography, and molecular dynamics simulations suggest that these flexible N-terminal regions enhance thermal resilience without affecting the catalytic rate or oligomerization in some homologs, while they promote oligomerization and reduce kcat in others. These findings suggest that flexible terminal regions can act as modular stabilizing elements through diverse mechanisms. Our work provides mechanistic insight into an unusual route to protein thermostability, expanding strategies for enzyme engineering, and contributing to the development of robust biocatalysts for polyester degradation.