Enzymes function as biocatalysts and are extensively exploited in industrial applications. Immobilization of enzymes using support materials has been shown to improve enzyme properties, including stability and functionality in extreme conditions and recyclability in biocatalytic processing. This review focuses on the recent advances utilizing the design space of in vivo self-assembled polyhydroxyalkanoate (PHA) particles as biocatalyst immobilization scaffolds. Self-assembly of biologically active enzyme-coated PHA particles is a one-step in vivo production process, which avoids the costly and laborious in vitro chemical cross-linking of purified enzymes to separately produced support materials. The homogeneous orientation of enzymes densely coating PHA particles enhances the accessibility of catalytic sites, improving enzyme function. The PHA particle technology has been developed into a remarkable scaffolding platform for the design of cost-effective designer biocatalysts amenable toward robust industrial bioprocessing. In this review, the PHA particle technology will be compared to other biological supramolecular assembly-based technologies suitable for in vivo enzyme immobilization. Recent progress in the fabrication of biological particulate scaffolds using enzymes of industrial interest will be summarized. Additionally, we outline innovative approaches to overcome limitations of in vivo assembled PHA particles to enable finetuned immobilization of multiple enzymes to enhance performance in multi-step cascade reactions, such as those used in continuous flow bioprocessing.
Immobilization and display of proteins is extensively used to enhance stability and performance of proteins for technical uses such as in biotechnology. Here, self‐assembled nonporous polyhydroxybutyrate (PHB) particles bioengineered to display proteins of interest are subjected to alginate encapsulation processes. The novel composite spheres are fabricated using ionotropic gelation methods. The immunoglobulin G (IgG) binding domain Z and organophosphate hydrolase (OpdA) are attached to PHB particles, and are examples for bioseparation and bioremediation applications, respectively. Alginate microspheres entrapping Z domain coated PHB particles enable flow‐through purification of IgG. Microsphere porosity is pH tunable and at acidic pH IgG is released from Z domains but retained within microspheres. OpdA‐PHB particles are functionally entrapped in alginate microspheres enabling flow‐through substrate conversion. Attachment of functional proteins to PHB particles enhances retention within the alginate microspheres. The hydrophobic PHB particle core within alginate beads provides payload for lipophilic substances, which adsorption kinetics are aligned with a pseudo‐second‐order kinetic model in agreement with the Freundlich isotherm model. This study describes the development of a multifunctional composite material platform based on alginate spheres encapsulating PHB particles that provide payload for lipophilic substances and can be engineered to display protein functions of interest.
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