Engineered Sphingomonas sp. KT-1 PahZ1 monomers efficiently degrade poly(aspartic acid)

In recent years, there has been an effort toward creating and utilizing novel biodegradable polymeric materials. As products become available, it is necessary to concurrently search for novel biodegradation catalysts and further investigate the properties of known biodegradation enzymes. Regarding the latter, we recently reported the crystal structure of a dimeric enzyme, Sphingomonas sp. KT-1 PahZ1, capable of degrading poly(aspartic acid), a green alternative to non-biodegradable polycarboxylates. However, the role of the dimeric state in catalytic function remained unclear. Here we report PahZ1_KT-1 constructs with either single or multiple mutation(s) at the dimer interface yield active monomers. Our data indicates PahZ1_KT-1 monomers and dimers catalyze PAA degradation at equivalent rates. Unfolding experiments reveal differences where the activation energy for monomers is ~ 46 kJ mol^-1 lower than for dimers despite similar thermodynamic properties. Characterization of this biodegradation enzyme and others is critical for future protein engineering efforts toward polymer remediation.