Supreme Catalytic Properties of Enzyme Nanoparticles Based on Ferritin Self-Assembly

An efficient strategy to tailor PET hydrolase: Simple preparation with high yield and enhanced hydrolysis to micro-nano plastics

Polyethylene terephthalate (PET) nano/microplastics (PET-NMPs) are regarded as an emergent hazardous waste for the environment. Enzymatic treatment of PET-NMPs is one of the most promising methods. However, strategies for mining or engineering of PET hydrolases with better characteristics and the simple and cost-effective preparation of them are the bottlenecks currently. Herein, we proposed a gene fusion strategy to tailor PET hydrolase (ICCG) with ferritin (namely F-C) towards micro-nano PET degradation. The purified F-C was obtained by an easy scalable low-speed centrifugation with 80.8 % activity recovery and 82.9 % protein recovery compared to the crude protein extraction, with the final high yield of 2.17 g/L. Encouragingly, unlike only hydrolyzing amorphous PET (crystallinity lower than 10 %), the resulted F-C showed 84.53 mgTPA/h/mgEnzyme specific activity at 70 °C for 5 h towards micro-PET with relatively high crystallinity (20.54 %) at the optimized enzyme/PET ratio of 1:100 (Wt), without producing intermediates. The supreme activity of F-C was closely related to its enhanced affinity towards substrate, increased substrate's ester bond tensions and binding pocket volume. More interestingly, F-C exhibited promising stability not only in storage or high temperature, but also in simulated seawater (hypersaline environment), with the half-lives of 128.4 days at 30 °C. Thus, the all-in-one strategy will offer a green and alternative solution to assist the PET-NMPs waste treatments such as recycling in the high-temperature reactor or degradation in seawater.

Self-assembly systems to troubleshoot metabolic engineering challenges

Enzyme self-assembly is a technology in which enzyme units can aggregate into ordered macromolecules, assisted by scaffolds. In metabolic engineering, self-assembly strategies have been explored for aggregating multiple enzymes in the same pathway to improve sequential catalytic efficiency, which in turn enables high-level production. The performance of the scaffolds is critical to the formation of an efficient and stable assembly system. This review comprehensively analyzes these scaffolds by exploring how they assemble, and it illustrates how to apply self-assembly strategies for different modules in metabolic engineering. Functional modifications to scaffolds will further promote efficient strategies for production.

Controlled co-immobilisation of proteins via 4'-phosphopantetheine-mediated site-selective covalent linkage

In Escherichia coli, acyl carrier protein (ACP) is posttranslationally converted into its active holo-ACP form via covalent linkage of 4'-phosphopantetheine (4'-PP) to residue serine-36. We found that the long flexible 4'-PP arm could react chemoselectively with the iodoacetyl group introduced on solid supports with high efficiency under mild conditions. Based on this finding, we developed site-selective immobilisation of proteins via the active holo-ACP fusion tag, independently of the physicochemical properties of the protein of interest. Furthermore, the molecular ratios of co-immobilised proteins can be manipulated because the tethering process is predominantly directed by the molar concentrations of diverse holo-ACP fusions during co-immobilisation. Conveniently tuning the molecular ratios of co-immobilised proteins allows their cooperation, leading to a highly productive multi-protein co-immobilisation system. Kinetic studies of enzymes demonstrated that α-amylase (Amy) and methyl parathion hydrolase (MPH) immobilised via active tag holo-ACP had higher catalytic efficiency (k_cat/Km) in comparison with their corresponding counterparts immobilised via the sulfhydryl groups (-SH) of these proteins. The immobilised holo-ACP-Amy also presented higher thermostability compared with free Amy. The enhanced α-amylase thermostability upon immobilisation via holo-ACP renders it more suitable for industrial application.