Catenane versus ring: do both assemblies of CS2 hydrolase exhibit the same stability and catalytic activity?

Abstract

Catenane structures, in which two or more rings are mechanically interlocked, have historically occupied one of the central places in the field of supramolecular chemistry. In contrast to synthetic small-molecule catenanes, examples of naturally-occurring catenanes are scarce. Here, we report thermodynamic and enzymatic studies on CS₂ hydrolase, which exists in solution as a mixture of unique hexadecameric catenane and octameric ring forms. A combination of field-flow fractionation coupled to multi-angle laser light scattering (FFF-MALLS) and native mass spectrometric analyses revealed that the catenane form is converted into the ring form at elevated temperatures, whereas the ring does not assemble into the catenane under the same conditions. Measurements of the enzyme kinetics for the conversion of CS₂ into COS and H₂S showed that the ring form of CS₂ hydrolase possesses higher enzyme efficiency (per monomer) than the catenane form, whereas the catenane form is overall more active (per assembly).