•To optimize the substrate binding site of IsPETase, we compared the residues constituting the substrate binding site with those from other PETase candidates.•IsPETaseS242T and IsPETaseN246D variants ...showed increased PET degradation activity.•We introduced S242 T and N246D to the IsPETaseS121E/D186H/R280A variant developed in the previous paper and generated the IsPETaseS121E/D186H/S242T/N246D variant with PET degradation activity increased by 58-fold compared to IsPETaseWT.
Poly(ethylene terephthalate) (PET), a widely used plastic around the world, causes various environmental and health problems. Several groups have been extensively conducting research to solve these problems through enzymatic degradation of PET at high temperatures around 70 °C. Recently, Ideonella sakaiensis, a bacterium that degrades PET at mild temperatures, has been newly identified, and further protein engineering studies on the PET degrading enzyme from the organism (IsPETase) have also been conducted to overcome the low thermal stability of the enzyme. In this study, we performed structural bioinformatics-based protein engineering of IsPETase to optimize the substrate binding site of the enzyme and developed two variants, IsPETaseS242T and IsPETaseN246D, with higher enzymatic activity at both 25 and 37 °C compared with IsPETaseWT. We also developed the IsPETaseS121E/D186H/S242T/N246D variant by integrating the S242 T and N246D mutations into the previously reported IsPETaseS121E/D186H/R208A variant. At the 37 °C incubation, the quadruple variant maintained the PET degradation activity for 20 days, unlike IsPETaseWT that lost its activity within a day. Consequently, this study exhibited 58-fold increase in the activity compared with IsPETaseWT.
The development of a superb polyethylene terephthalate (PET) hydrolyzing enzyme requires an accurate understanding of the PET decomposition mechanism. However, studies on PET degrading enzymes, ...including the PET hydrolase from Ideonella sakaiensis (IsPETase), have not provided sufficient knowledge of the molecular mechanisms for the hardly accessible substrate. Here, we report a novel PET hydrolase from Rhizobacter gummiphilus (RgPETase), which has a hydrolyzing activity similar to IsPETase toward microcrystalline PET but distinct behavior toward low crystallinity PET film. Structural analysis of RgPETase reveals that the enzyme shares the key structural features of IsPETase for high PET hydrolysis activity but has distinguished structures at the surface-exposed regions. RgPETase shows a unique conformation of the wobbling tryptophan containing loop (WW-loop) and change of the electrostatic surface charge on the loop dramatically affects the PET-degrading activity. We further show that effect of the electrostatic surface charge to the activity varies depending on locations. This work provides valuable information underlying the uncovered PET decomposition mechanism.
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•Identification of a mesophilic PET hydrolase from Rhizobacter gummiphilus.•Report on distinct behavior of homologous PET hydrolases toward different PET samples.•Structural comparison of the mesophilic PET hydrolases implying uncovered mechanism.
Poly(ethylene terephthalate) (PET) is the most commonly used polyester polymer resin in fabrics and storage materials, and its accumulation in the environment is a global problem. The ability of PET ...hydrolase from Ideonella sakaiensis 201-F6 (IsPETase) to degrade PET at moderate temperatures has been studied extensively. However, due to its low structural stability and solubility, it is difficult to apply standard laboratory-level IsPETase expression and purification procedures in industry. To overcome this difficulty, the expression of IsPETase can be improved by using a secretion system. This is the first report on the production of an extracellular IsPETase, active against PET film, using Sec-dependent translocation signal peptides from E. coli. In this work, we tested the effects of fusions of the Sec-dependent and SRP-dependent signal peptides from E. coli secretory proteins into IsPETase, and successfully produced the extracellular enzyme using pET22b-SPMalE:IsPETase and pET22b-SPLamB:IsPETase expression systems. We also confirmed that the secreted IsPETase has PET-degradation activity. The work will be used for development of a new E. coli strain capable of degrading and assimilating PET in its culture medium.
•PETase from Ideonella sakaiensis (IsPETase) was successfully produced using the protein secretory expression system.•Extracellular production of IsPETase is achieved by sec-dependent secretion system.•The extracellularly produced IsPETase shows a PET degradation activity.
Dehydroquinate dehydratase (DHQD) catalyzes the conversion of 3-dehydroquinic acid (DHQ) into 3-dehydroshikimic acid in the mid stage of the shikimate pathway, which is essential for the biosynthesis ...of aromatic amino acids and folates. Here, we report two the crystal structures of type II DHQD (CgDHQD) derived from Corynebacterium glutamicum, which is a widely used industrial platform organism. We determined the structures for CgDHQD WT with the citrate at a resolution of 1.80A and CgDHQD R19A with DHQ complexed forms at a resolution of 2.00 A, respectively. The enzyme forms a homododecamer consisting of four trimers with three interfacial active sites. We identified the DHQ-binding site of CgDHQD and observed an unusual binding mode of citrate inhibitor in the site with a half-opened lid loop. A structural comparison of CgDHQD with a homolog derived from Streptomyces coelicolor revealed differences in the terminal regions, lid loop, and active site. Particularly, CgDHQD, including some Corynebacterium species, possesses a distinctive residue P105, which is not conserved in other DHQDs at the position near the 5-hydroxyl group of DHQ. Replacements of P105 with isoleucine and valine, conserved in other DHQDs, caused an approximately 70% decrease in the activity, but replacement of S103 with threonine (CgDHQD S103T ) caused a 10% increase in the activity. Our biochemical studies revealed the importance of key residues and enzyme kinetics for wild type and CgDHQD S103T , explaining the effect of the variation. This structural and biochemical study provides valuable information for understanding the reaction efficiency that varies due to structural differences caused by the unique sequences of CgDHQD.
Sphingobium sp. strain SYK-6, an aerobic gram-negative bacillus found in soil, is known for utilizing lignin-derived monoaryls and biaryls as carbon sources and degrading aromatic compounds. The ...Sphingobium sp. strain SYK-6 genome contains three genes involved in salicylate catabolism: SLG_11260, SLG_11270, and SLG_11280. Here, we report that the gene product of SLG_11280 functions as a maleylpyruvate hydrolase (SsMPH) with Km and Kcat values of 166.2 μM and 3.76 min−1, respectively. This study also reveals the crystal structures of both the apo and pyruvate-manganese ion-bound SsMPH, which revealed that like other fumarylacetoacetate hydrolases, SsMPH dimerizes and has nine unique 310-helices. Molecular docking studies of maleylpyruvate also revealed the likely binding mode of SsMPH and its substrate.
•The gene product of SLG_11280 functions as a maleylpyruvate hydrolase.•The Km and Kcat values of SsMPH for maleylpyruvate were 166.2 μM and 3.76 min-1, respectively.•The first crystal structure of maleylpyruvate hydrolase was determined.
The Lonely Guy (LOG) protein has been identified as a crucial enzyme involved in the production of cytokinins, which are important phytohormones, in plants and plant-interacting organisms. However, ...C. glutamicum has an isoform (Cg1261) of LOG that contains an extended N-terminal region compared to those of known LOGs, and this type of isoforms are also found in a variety of organisms. Nevertheless, these proteins are considered as lysine decarboxylases, without their functional characterization. To investigate the function of Cg1261, we determined its crystal structure at a resolution of 1.95 Å. Unlike known dimeric LOGs, Cg1261 was found to form a hexamer. The overall shape of the hexamer resembles a trillium flower, in which a twisted dimer constitutes each petal. The dimeric petal is well superposed with known LOG dimers, and its active site conformation is similar to those of LOG dimers, suggesting that the hexameric LOG-like protein also acts as a LOG. Biochemical and in vivo cytokinin production studies on Cg1261 confirms that Cg1261 functions as a cytokinin-activating protein. Phylogenetic tree analysis using 123 LOG-like proteins suggest that the LOG-like proteins can be categorized to the dimeric type-I LOG and the hexameric type-II LOG.
Monohydroxyethyl terephthalate (MHET) hydrolase (MHETase) is an enzyme known to be involved in the final degradation step of poly(ethylene terephthalate) (PET) by hydrolyzing MHET into terephthalic ...acid and ethylene glycol in Ideonella sakaiensis. Here, we report the extracellular production of MHETase in an active form with a proper folding. Based on the structural observations and biochemical experiments, we reveal that MHETase also functions as exo-PETase by hydrolyzing the synthesized PET pentamer. We further present that MHETase has a hydrolysis activity against the termini-generated PET film, demonstrating the exo-PETase function of the enzyme. We also develop a MHETaseR411K/S416A/F424I variant with a higher BHET activity, and the variant exhibits an enhanced degradation activity against the PET film. Based on these results, we propose that MHETase plays several roles in the biodegradation of PET using the BHETase and exo-PETase activities as well as the MHET hydrolysis function.
Pseudomonas aeruginosa PAO1 can utilize various aromatic hydrocarbons as a carbon source. Among the three genes involved in the gentisate pathway of P. aeruginosa, the gene product of PA2473 belongs ...to the ζ-class glutathione S-transferase and is predicted to be a maleylpyruvate isomerase. In this study, we determined the crystal structure of maleylpyruvate isomerase from Pseudomonas aeruginosa PAO1 (PaMPI) at a resolution of 1.8 Å. PaMPI functions as a dimer and shows the glutathione S-transferase fold. The structure comparison with other glutathione S-transferase structures enabled us to predict the glutathione cofactor binding site and suggests that PaMPI has differences in residues that make up the putative substrate binding site. Biochemical study of PaMPI showed that the protein has an MPI activity. Interestingly, unlike the reported glutathione S-transferases so far, the purified PaMPI showed isomerase activity without the addition of the reduced glutathione, although the protein showed much higher activity when the glutathione cofactor was added to the reaction mixture. Taken together, our studies reveal that the gene product of PA2473 functions as a maleylpyruvate isomerase and might be involved in the gentisate pathway.
•Crystal structure of maleylpyruvate isomerase from Pseudomonas aeruginosa PAO1 was determined.•The gene product of PA2473 functions as a maleylpyruvate isomerase and might be involved in the gentisate pathway.•Based on the structural comparisons, we suggested the formation of the cofactor and substrate binding site of PaMPI.
Carbohydrates are structurally and functionally diverse materials including polysaccharides, and marine organisms are known to have many enzymes for the breakdown of complex polysaccharides. Here, we ...identified an α-l-fucosidase enzyme from the marine bacterium Vibrio sp. strain EJY3 (VejFCD) that has dual α-1,4-glucosidic and β-1,4-galactosidic specificities. We determined the crystal structure of VejFCD and provided the structural basis underlying the dual α- and β-glycosidase activities of the enzyme. Unlike other three-domain FCDs, in VejFCD, carbohydrate-binding module-B (CBM-B) with a novel β-sandwich fold tightly contacts with the CatD/CBM-B main body and provides key residues for the β-1,4-glycosidase activity of the enzyme. The phylogenetic tree analysis suggests that only a few FCDs from marine microorganisms have the key structural features for dual α-1,4- and β-1,4-glycosidase activities. This study provides the structural insights into the mechanism underlying the novel glycoside hydrolase activities and could be applied for more efficient utilization in the hydrolysis of complex carbohydrates in biotechnological applications.
Biodegradation of polyethylene terephthalate (PET) is one of fundamental ways to solve plastic pollution. As various microbial hydrolases have an extra domain unlike PETase from Ideonella sakaiensis ...(IsPETase), research on the role of these extra domain in PET hydrolysis is crucial for the identification and selection of a novel PET hydrolase. Here, we report that a PET hydrolase from Burkholderiales bacterium RIFCSPLOWO2_02_FULL_57_36 (BbPETase) with an additional N-terminal domain (BbPETaseAND) shows a similar hydrolysis activity toward microcrystalline PET and a higher thermal stability than IsPETase. Based on detailed structural comparisons between BbPETase and IsPETase, we generated the BbPETaseS335N/T338I/M363I/N365G variant with an enhanced PET-degrading activity and thermal stability. We further revealed that BbPETaseAND contributes to the thermal stability of the enzyme through close contact with the core domain, but the domain might hinder the adhesion of enzyme to PET substrate. We suggest that BbPETase is an enzyme in the evolution of efficient PET degradation and molecular insight into a novel PET hydrolase provides a novel strategy for the development of biodegradation of PET.
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•Investigation of an auxiliary domain-containing PET hydrolase.•Development of a PET hydrolase with enhanced enzyme activity and thermal stability.•Structural and functional roles of auxiliary domain in PET decomposition.
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