A multidomain hydrolase from the thermophile Thermanaeromonas toyohensis degrades high molecular mass forms of polyhydroxybutyrate.

The use of polyhydroxybutyrate (PHB) bioplastics has the potential to create a circular and sustainable recycling plastic system. Here, we focus on PHB degradation and characterize the multidomain PHB hydrolyzing enzyme from the extremophile Thermanaeromonas tohohensis. The catalytic domain fold is conserved across a diverse taxonomic range, but the C-terminal domains are unique amongst PHBases and instead share similarities with carbohydrate degrading enzymes from human gut microbiota. The enzyme has a preference for higher molecular weight PHB. Hydrolysis of PHB films correlates with the ability of the enzyme to bind those films, most likely driven by its C-terminal substrate binding domain. The enzyme denatures in a highly cooperative manner over a short temperature range, and the kinetics of folding/unfolding are well described by Eyring theory. Finally, the study of this enzyme has been incorporated into an undergraduate biochemistry teaching laboratory that focuses on "real life" research problems with relevance to industry.