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Rhodium-Complex-Linked Hybrid Biocatalyst: Stereo-Controlled Phenylacetylene Polymerization within an Engineered Protein Cavity



The incorporation of a Rh complex with a maleimide moiety into the cavity of the nitrobindin β-barrel scaffold by a covalent linkage at the 96-position (Cys) provides a hybrid biocatalyst that promotes the polymerization of phenylacetylene. The appropriate structural optimization of the cavity by mutagenesis enhances the stereoselectivity of the polymer with a trans content of 82 % at 25 °C and pH 8.0. The X-ray crystal structure of one of the hybrid biocatalysts at a resolution of 2.0 Å reveals that the Rh complex is located in the β-barrel cavity without any perturbation to the total protein structure. Crystal structure analysis and molecular modeling support the fact that the stereoselectivity is enhanced by the effective control of monomer access to the Rh complex within the limited space of the protein cavity.