Plastics, including poly(ethylene terephthalate) (PET), possess many desirable characteristics and thus are widely used in daily life. However, non-biodegradability, once thought to be an advantage offered by plastics, is causing major environmental problem. Recently, a PET-degrading bacterium, Ideonella sakaiensis, was identified and suggested for possible use in degradation and/or recycling of PET. However, the molecular mechanism of PET degradation is not known. Here we report the crystal structure of I. sakaiensis PETase (IsPETase) at 1.5 Å resolution. IsPETase has a Ser–His-Asp catalytic triad at its active site and contains an optimal substrate binding site to accommodate four monohydroxyethyl terephthalate (MHET) moieties of PET. Based on structural and site-directed mutagenesis experiments, the detailed process of PET degradation into MHET, terephthalic acid, and ethylene glycol is suggested. Moreover, other PETase candidates potentially having high PET-degrading activities are suggested based on phylogenetic tree analysis of 69 PETase-like proteins.

Widespread utilization of polyethylene terephthalate (PET) has caused a variety of environmental and health problems; thus, the enzymatic degradation of PET can be a promising solution. Although PETase from Ideonalla sakaiensis (IsPETase) has been reported to have the highest PET degradation activity under mild conditions of all PET-degrading enzymes reported to date, its low thermal stability limits its ability for efficient and practical enzymatic degradation of PET. Using the structural information on IsPETase, we developed a rational protein engineering strategy using several IsPETase variants that were screened for high thermal stability to improve PET degradation activity. In particular, the IsPETaseS121E/D186H/R280A variant, which was designed to have a stabilized β6-β7 connecting loop and extended subsite IIc, had a T m value that was increased by 8.81 °C and PET degradation activity was enhanced by 14-fold at 40 °C in comparison with IsPETaseWT. The designed structural modifications were further verified through structure determination of the variants, and high thermal stability was further confirmed by a heat-inactivation experiment. The proposed strategy and developed variants represent an important advancement for achieving the complete biodegradation of PET under mild conditions.

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Inflammatory cytokines, matrix metalloproteinases (MMPs) and cyclooxygenase (COX)-2 released from rheumatoid arthritis synovial fibroblasts (RASFs) are involved in the destruction of both articular bone and cartilage. Kaempferol has been reported to act as an antioxidant and anti-inflammatory agent by inhibiting nitric oxide synthase and COX enzymes. The aim of the present study was to determine the effects of kaempferol on the interleukin-1β (IL-1β)-induced proliferation of RASFs and the production of MMPs, COX and prostaglandin E2 (PGE2) by RASFs. The proliferation of the RASFs stimulated with IL-1β and treated with/without kaempferol was evaluated by CCK-8 assay. The expression of MMPs, TIMP metallopeptidase inhibitor-1 (TIMP-1), COXs, PGE2 and that of intracellular MAPK signaling molecules, including p-ERK, p-p38, p-JNK and nuclear factor-κB (NF-κB) was examined by immunoblotting or semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) and ELISA under the conditions described above. Kaempferol inhibited the proliferation of both unstimulated and IL-1β‑stimulated RASFs, as well as the mRNA and protein expression of MMP-1, MMP-3, COX-2 and PGE2 induced by IL-1β. Kaempferol also inhibited the phosphorylation of ERK-1/2, p38 and JNK, as well as the activation of NF-κB induced by IL-1β. These results indicate that kaempferol inhibits synovial fibroblast proliferation, as well as the production of and MMPs, COX‑2 and PGE2, which is involved in articular inflammation and destruction in rheumatoid arthritis (RA). Our data suggest that kaempferol may be a novel therapeutic agent for the treatment of RA.

Escherichia coli was metabolically engineered to produce industrially important platform chemicals, 3-hydroxypropionic acid (3-HP) and malonic acid (MA), through the β-alanine (BA) route. First, various combinations of downstream enzymes were screened and BA pyruvate transaminase (encoded by pa0132) from P. aeruginosa was selected to generate malonic semialdehyde (MSA) from BA. This platform strain was engineered by introducing E. coli MSA reductase (encoded by ydfG) to reduce MSA to 3-HP. Replacement of native promoter of the sdhC gene with the strong trc promoter in the genome increased 3-HP production to 3.69 g/L in flask culture. Introduction of E. coli semialdehyde dehydrogenase (encoded by yneI) into the platform strain resulted in the production of MA, and additional deletion of the ydfG gene increased MA production to 0.450 g/L in flask culture. Fed-batch cultures of final engineered strains resulted in the production of 31.1 g/L 3-HP or 3.60 g/L MA from glucose.

Microorganisms produce diverse polymers for various purposes such as storing genetic information, energy, and reducing power, and serving as structural materials and scaffolds. Among these polymers, polyhydroxyalkanoates (PHAs) are microbial polyesters synthesized and accumulated intracellularly as a storage material of carbon, energy, and reducing power under unfavorable growth conditions in the presence of excess carbon source. PHAs have attracted considerable attention for their wide range of applications in industrial and medical fields. Since the first discovery of PHA accumulating bacteria about 100 years ago, remarkable advances have been made in the understanding of PHA biosynthesis and metabolic engineering of microorganisms toward developing efficient PHA producers. Recently, nonnatural polyesters have also been synthesized by metabolically engineered microorganisms, which opened a new avenue toward sustainable production of more diverse plastics. Herein, the current state of PHAs and nonnatural polyesters is reviewed, covering mechanisms of microbial polyester biosynthesis, metabolic pathways, and enzymes involved in biosynthesis of short‐chain‐length PHAs, medium‐chain‐length PHAs, and nonnatural polyesters, especially 2‐hydroxyacid‐containing polyesters, metabolic engineering strategies to produce novel polymers and enhance production capabilities and fermentation, and downstream processing strategies for cost‐effective production of these microbial polyesters. In addition, the applications of PHAs and prospects are discussed.

Pseudomonas putida has gained much interest among metabolic engineers as a workhorse for producing valuable natural products. While a few gene knockout tools for P. putida have been reported, integration of heterologous genes into the chromosome of P. putida, an essential strategy to develop stable industrial strains producing heterologous bioproducts, requires development of a more efficient method. Current methods rely on time-consuming homologous recombination techniques and transposon-mediated random insertions. Here we report a RecET recombineering system for markerless integration of heterologous genes into the P. putida chromosome. The efficiency and capacity of the recombineering system were first demonstrated by knocking out various genetic loci on the P. putida chromosome with knockout lengths widely spanning 0.6-101.7 kb. The RecET recombineering system developed here allowed successful integration of biosynthetic gene clusters for four proof-of-concept bioproducts, including protein, polyketide, isoprenoid, and amino acid derivative, into the target genetic locus of P. putida chromosome. The markerless recombineering system was completed by combining Cre/lox system and developing efficient plasmid curing systems, generating final strains free of antibiotic markers and plasmids. This markerless recombineering system for efficient gene knockout and integration will expedite metabolic engineering of P. putida, a bacterial host strain of increasing academic and industrial interest.

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