Succinic acid (SA), a dicarboxylic acid of industrial importance, can be efficiently produced by metabolically engineered Mannheimia succiniciproducens. Malate dehydrogenase (MDH) is one of the key ...enzymes for SA production, but has not been well characterized. Here we report biochemical and structural analyses of various MDHs and development of hyper-SA producing M. succiniciproducens by introducing the best MDH. Corynebacterium glutamicum MDH (CgMDH) shows the highest specific activity and least substrate inhibition, whereas M. succiniciproducens MDH (MsMDH) shows low specific activity at physiological pH and strong uncompetitive inhibition toward oxaloacetate (ki of 67.4 and 588.9 μM for MsMDH and CgMDH, respectively). Structural comparison of the two MDHs reveals a key residue influencing the specific activity and susceptibility to substrate inhibition. A high-inoculum fed-batch fermentation of the final strain expressing cgmdh produces 134.25 g L
of SA with the maximum productivity of 21.3 g L
h
, demonstrating the importance of enzyme optimization in strain development.
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.
Excessive polyethylene terephthalate (PET) waste causes a variety of problems. Extensive research focused on the development of superior PET hydrolases for PET biorecycling has been conducted. ...However, template enzymes employed in enzyme engineering mainly focused on IsPETase and leaf-branch compost cutinase, which exhibit mesophilic and thermophilic hydrolytic properties, respectively. Herein, we report a PET hydrolase from Cryptosporangium aurantiacum (CaPETase) that exhibits high thermostability and remarkable PET degradation activity at ambient temperatures. We uncover the crystal structure of CaPETase, which displays a distinct backbone conformation at the active site and residues forming the substrate binding cleft, compared with other PET hydrolases. We further develop a CaPETase
variant that exhibits robust thermostability with a T
of 83.2 °C and 41.7-fold enhanced PET hydrolytic activity at 60 °C compared with CaPETase
. CaPETase
almost completely decompose both transparent and colored post-consumer PET powder at 55 °C within half a day in a pH-stat bioreactor.
Genome editing is crucial for genetic engineering of organisms for improved traits, particularly in microalgae due to the urgent necessity for the next generation biofuel production. The most ...advanced CRISPR/Cas9 system is simple, efficient and accurate in some organisms; however, it has proven extremely difficult in microalgae including the model alga Chlamydomonas. We solved this problem by delivering Cas9 ribonucleoproteins (RNPs) comprising the Cas9 protein and sgRNAs to avoid cytotoxicity and off-targeting associated with vector-driven expression of Cas9. We obtained CRISPR/Cas9-induced mutations at three loci including MAA7, CpSRP43 and ChlM, and targeted mutagenic efficiency was improved up to 100 fold compared to the first report of transgenic Cas9-induced mutagenesis. Interestingly, we found that unrelated vectors used for the selection purpose were predominantly integrated at the Cas9 cut site, indicative of NHEJ-mediated knock-in events. As expected with Cas9 RNPs, no off-targeting was found in one of the mutagenic screens. In conclusion, we improved the knockout efficiency by using Cas9 RNPs, which opens great opportunities not only for biological research but also industrial applications in Chlamydomonas and other microalgae. Findings of the NHEJ-mediated knock-in events will allow applications of the CRISPR/Cas9 system in microalgae, including "safe harboring" techniques shown in other organisms.
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 (
DHQD) derived from
, which is a widely used industrial platform organism. We determined the structures for
DHQD
with the citrate at a resolution of 1.80Å and
DHQD
with DHQ complexed forms at a resolution of 2.00 Å, respectively. The enzyme forms a homododecamer consisting of four trimers with three interfacial active sites. We identified the DHQ-binding site of
DHQD and observed an unusual binding mode of citrate inhibitor in the site with a half-opened lid loop. A structural comparison of
DHQD with a homolog derived from
revealed differences in the terminal regions, lid loop, and active site. Particularly,
DHQD, including some
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 (
DHQD
) caused a 10% increase in the activity. Our biochemical studies revealed the importance of key residues and enzyme kinetics for wild type and
DHQD
, 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
DHQD.
Amylomaltase is an essential enzyme in maltose utilization and maltodextrin metabolism, and it has been industrially used for the production of cyclodextrin and modification of starch. We determined ...the crystal structure of amylomaltase from Corynebacterium glutamicum (CgAM) at a resolution of 1.7 Å. Although CgAM forms a dimer without NaCl, it exists as a monomer in physiological concentration of NaCl. CgAM is composed of N- and C-terminal domains, which can be further divided into two and four subdomains, respectively. It exhibits a unique structural feature at the functionally unknown N-domain and also shows two striking differences at the C-domain compared to other amylomaltases. These differences at extended edge of the substrate-binding site might affect substrate specificity for large cyclodextrin formation. The bis-tris methane and sulfate molecules bound at the substrate-binding site of our current structure mimic the binding of the hydroxyl groups of glucose bound at subsites −1 and −2, respectively.
Although enoyl-CoA hydratase/isomerase superfamily proteins are functionally diverse and extremely abundant in microbial and higher organism’s genome, they still have been elusively annotated. The ...genome of
Cupriavidus necator
H16 contains at least 54 enoyl-CoA hydratase/isomerase superfamily proteins that might influence on polyhydroxyalkanoate synthesis, but most of them are uncharacterized. Among them, we first determined crystal structure of H16_B0756 at a 2.0 Å resolution. The protein exhibits unique amino acid sequences compared to the other isoforms with identity lower than 36%. The structure of H16_B0756 forms a trimeric architecture and showed canonical disk-shape. Interestingly, H16_B0756 has only one glutamate residue at the active site while other enoyl-CoA hydratases have two nucleophilic glutamate at the catalytic site. We found that the active site conformation of H16_B0756 is quite similar to that of 1,2-epoxyphenylacetyl-CoA isomerase (PaaG) rather than those of other enoyl-CoA hydratases. In addition to the structural comparison, gene neighborhoods analysis suggested that H16_B0756 might function in the ring compound degradation.
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.
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