Thomas_2022_Protein.Sci__e4470

As the epidemic of single-use plastic worsens, it has become critical to identify fully renewable plastics such as those that can be degraded using enzymes. Here we describe the structure and biochemistry of an alkaline poly[(R)-3-hydroxybutyric acid] (PHB) depolymerase from the soil thermophile Lihuaxuella thermophila. Like other PHB depolymerases or PHBases, the Lihuaxuella enzyme is active against several different polyhydroxyalkanoates, including homo- and heteropolymers, but L. thermophila PHB depolymerase (LtPHBase) is unique in that it also hydrolyzes polylactic acid and polycaprolactone. LtPHBase exhibits optimal activity at 70 degreesC, and retains 88% of activity upon incubation at 65 degreesC for three days. The 1.2 A resolution crystal structure reveals an alpha/beta-hydrolase fold typical of PHBases, but with a shallow active site containing the catalytic Ser-His-Asp-triad that appears poised for broad substrate specificity. LtPHBase holds promise for depolymerization of PHB and related bioplastics at high temperature, as would be required in bioindustrial operations like recycling or landfill management. This article is protected by copyright. All rights reserved.