Understanding the\nCatalytic Efficiency of Two Polyester\nDegrading Enzymes: An Experimental and Theoretical Investigation

The discovery of\nnovel plastic degrading enzymes commonly\nrelies\non comparing features of the primary sequence to those of known plastic\ndegrading enzymes. However, this approach cannot always guarantee\nsuccess. This is exemplified by the different degradation rates of\nthe two polymers poly(ethylene terephthalate) (PET) and polybutylene\nsuccinate (PBS) by two hydrolases: <i>Is</i>PETase from <i>Ideonella sakaiensis</i> and <i>Ad</i>Cut from <i>Acidovorax delafieldii</i>. Despite the enzymes showing a very\nhigh sequence identity of 82%, <i>Is</i>PETase shows significant\nhydrolysis activity for both polymers, whereas <i>Ad</i>Cut only shows significant hydrolysis activity for PBS. By solving\nthe structure of <i>Ad</i>Cut using X-ray crystallography,\nand using this as the basis for computer simulations, comparisons\nare made between the differences in the calculated binding geometries\nand the catalytic results obtained from biochemical experiments. The\nresults reveal that the low activity of <i>Ad</i>Cut toward\nPET can be explained by the low sampling of the productive conformation\nobserved in the simulations. While the active site serine in <i>Is</i>PETase can closely encounter the PET carbonyl carbon,\nin <i>Ad</i>Cut it cannot: a feature that can be attributed\nto the shape of the catalytic binding pocket. These results yield\nan important insight into the design requirements for novel plastic\ndegrading enzymes, as well as showing that computational methods can\nbe used as a valuable tool in understanding the molecular basis for\ndifferent hydrolysis activities in homologous polyesterase enzymes.