His-Tag Immobilization of Cutinase 1 From Thermobifida cellulosilytica for Solvent-Free Synthesis of Polyesters

Abstract

For many years, lipase B from Candida antarctica (CaLB) was the primary biocatalyst used for enzymatic esterification and polycondensation reactions. More recently, the need for novel biocatalysts with different selectivity has arisen in the biotechnology and biocatalysis fields. The present work describes how the catalytic potential of Thermobifida cellulosilytica cutinase 1 (Thc_Cut1) was exploited for polyester synthesis. In a first step, Thc_Cut1 was immobilized on three different carriers, namely Opal, Coral, and Amber, using a novel non-toxic His-tag method based on chelated Fe(III) ions (>99% protein bounded). In a second step, the biocatalyzed synthesis of an array of aliphatic polyesters was conducted. A selectivity chain study in a solvent-free reaction environment showed how, in contrast to CaLB, Thc_Cut1 presents a certain preference for C₆ -C₄ ester-diol combinations reaching monomer conversions up to 78% and M_w of 878 g mol^-1 when the Amber immobilized Thc_Cut1 was used. The synthetic potential of this cutinase was also tested in organic solvents, showing a marked activity decrease in polar media like that observed for CaLB. Finally, recyclability studies were performed, which showed an excellent stability of the immobilized Thc_Cut1 (retained activity >94%) over 24 h reaction cycles when a solvent-free workup was used. Concerning a practical application of the biocatalyst's preparation, the production of oligomers with M_n values below 10 kDa is usually desired for the production of nanoparticles and for the synthesis of functional pre-polymers for coating applications that can be crosslinked in a second reaction step.

Keywords: cutinases; enzymatic synthesis; enzyme immobilization; green chemistry; polyesters.