Enhancing the activity of zearalenone lactone hydrolase toward the more toxic α-zearalanol via a single-point mutation

Zearalenone (ZEN) and its derivatives are estrogenic mycotoxins known to pose significant health threats to humans and animals. Especially, the derivative α-zearalanol (α-ZAL) is over 10 times more toxic than ZEN. Simultaneous degradation of ZEN and its derivatives, especially α-ZAL, using ZEN lactone hydrolases (ZHDs) is a promising solution to eliminate their potential hazards to food safety. However, most available ZHDs exhibit limited activity toward the more toxic α-ZAL compared to ZEN. Here, we identified a broad-substrate spectrum ZHD, named ZHDAY3, from Exophiala aquamarina CBS 119918, which could not only efficiently degrade ZEN but also exhibited 73% relative activity toward α-ZAL. Through rational design, we obtained the ZHDAY3(N153H) mutant, which exhibited the highest specific activity (253.3 ± 4.3 U/mg) reported so far for degrading α-ZAL. Molecular docking, structural comparative analysis, and kinetic analysis collectively suggested that the shorter distance between the side chain of the catalytic residue His242 and the lactone bond of α-ZAL and the increased binding affinity to the substrate were mainly responsible for the improved catalytic activity of ZHDAY3(N153H) mutant. This mechanism was further validated through additional molecular docking of 18 mutants and experimental verification of six mutants.IMPORTANCEThe mycotoxins zearalenone (ZEN) and its derivatives pose a significant threat to food safety. Here, we present a highly promising ZEN lactone hydrolase (ZHD), ZHDAY3, which is capable of efficiently degrading both ZEN and the more toxic derivative α-ZAL. Next, the ZHDAY3(N153H) mutant obtained by single-point mutation exhibited the highest specific activity for degrading α-ZAL reported thus far. We further elucidated the molecular mechanisms underlying the enhanced hydrolytic activity of ZHDAY3(N153H) toward α-ZAL. These findings represent the first investigation on the molecular mechanism of ZHDs against α-ZAL and are expected to provide a significant reference for further rational engineering of ZHDs, which will ultimately contribute to addressing the health risks and food safety issues posed by ZEN-like mycotoxins.

Enzymatic Synthesis of Noncanonical α-Amino Acids Containing γ-Tertiary Alcohols

Noncanonical amino acids (ncAAs) containing tertiary alcohols are valuable as precursors of natural products and active pharmaceutical ingredients. However, the assembly of such ncAA scaffolds from simple material by C-C bond formation remains a challenging task due to the presence of multiple stereocenters and large steric hindrance. In this study, we present a novel solution to this problem through highly selective enzymatic decarboxylative aldol addition. This method allows for the streamlined assembly of multifunctionalized ncAAs with γ-tertiary alcohols from readily available materials, such as L -aspartatic acid and isatins, vicinal diones and keto esters. The modularity of electrophiles furnished four classes of ncAAs with decent efficiency as well as excellent site and stereocontrol. Computational modeling was employed to gain detailed insight into the catalytic mechanism and to provide a rationale for the observed selectivities. The method offers a single-step approach to producing multifunctionalized ncAAs, which can be directly utilized in peptide synthesis and bioactivity assessment.

Reaction engineering blocks ether cleavage for synthesizing chiral cyclic hemiacetals catalyzed by unspecific peroxygenase

Hemiacetal compounds are valuable building blocks in synthetic chemistry, but their enzymatic synthesis is limited and often hindered by the instability of hemiacetals in aqueous environments. Here, we show that this challenge can be addressed through reaction engineering by using immobilized peroxygenase from Agrocybe aegerita (AaeUPO) under neat reaction conditions, which allows for the selective C-H bond oxyfunctionalization of environmentally significant cyclic ethers to cyclic hemiacetals. A wide range of chiral cyclic hemiacetal products are prepared in >99% enantiomeric excess and 95170 turnover numbers of AaeUPO. Furthermore, by changing the reaction medium from pure organic solvent to alkaline aqueous conditions, cyclic hemiacetals are in situ transformed into lactones. Lactams are obtained under the applied conditions, albeit with low enzyme activity. These findings showcase the synthetic potential of AaeUPO and offer a practical enzymatic approach to produce chiral cyclic hemiacetals through C-H oxyfunctionalization under mild conditions.

Phase II clinical trial of neoadjuvant anti-PD-1 (toripalimab) combined with axitinib in resectable mucosal melanoma

BACKGROUND

The outcome of patients with resectable mucosal melanoma is poor. Toripalimab combined with axitinib has shown impressive results in metastatic mucosal melanoma with an objective response rate of 48.3% and a median progression-free survival of 7.5 months in a phase Ib trial. It was hypothesized that this combination administered in the neoadjuvant setting might induce a pathologic response in resectable mucosal melanoma, so we conducted this trial.

PATIENTS AND METHODS

This single-arm phase II trial enrolled patients with resectable mucosal melanoma. Patients received toripalimab 3 mg/kg once every 2 weeks (Q2W) plus axitinib 5 mg two times a day (b.i.d.) for 8 weeks as neoadjuvant therapy, then surgery and adjuvant toripalimab 3 mg/kg Q2W starting 2 ± 1weeks after surgery for 44 weeks. The primary endpoint was the pathologic response rate according to the International Neoadjuvant Melanoma Consortium recommendations.

RESULTS

Between August 2019 and October 2021, 29 patients were enrolled and received treatment, of whom 24 underwent resection. The median follow-up time was 34.2 months (95% confidence interval 20.4-48.0 months). The pathologic response rate was 33.3% (8/24; 4 pathological complete responses and 4 pathological partial responses). The median event-free survival for all patients was 11.1 months (95% confidence interval 5.3-16.9 months). The median overall survival was not reached. Neoadjuvant therapy was tolerable with 8 (27.5%) grade 3-4 treatment-related adverse events and no treatment-related deaths. Tissue samples of 17 patients at baseline and after surgery were collected (5 responders and 12 nonresponders). Multiplex immunohistochemistry demonstrated a significant increase in CD3+ (P = 0.0032) and CD3+CD8+ (P = 0.0038) tumor-infiltrating lymphocytes after neoadjuvant therapy, particularly in pathological responders.

CONCLUSIONS

Neoadjuvant toripalimab combined with axitinib in resectable mucosal melanoma demonstrated a promising pathologic response rate with significantly increased infiltrating CD3+ and CD3+CD8+ T cells after therapy.

Computational Study of the Fries Rearrangement Catalyzed by Acyltransferase from Pseudomonas protegens

The acyltransferase from Pseudomonas protegens (PpATase) catalyzes in nature the reversible transformation of monoacetylphloroglucinol to diacetylphloroglucinol and phloroglucinol. Interestingly, this enzyme has been shown to catalyze the promiscuous transformation of 3-hydroxyphenyl acetate to 2',4'-dihydroxyacetophenone, representing a biological version of the Fries rearrangement. In the present study, we report a mechanistic investigation of this activity of PpATase using quantum chemical calculations. A detailed mechanism is proposed, and the energy profile for the reaction is presented. The calculations show that the acylation of the enzyme is highly exothermic, while the acetyl transfer back to the substrate is only slightly exothermic. The deprotonation of the C6-H of the substrate is rate-limiting, and a remote aspartate residue (Asp137) is proposed to be the general base group in this step. Analysis of the binding energies of various acetyl acceptors shows that PpATase can promote both intramolecular and intermolecular Fries rearrangement towards diverse compounds.

Construction of an artificial phosphoketolase pathway that efficiently catabolizes multiple carbon sources to acetyl-CoA

The canonical glycolysis pathway is responsible for converting glucose into 2 molecules of acetyl-coenzyme A (acetyl-CoA) through a cascade of 11 biochemical reactions. Here, we have designed and constructed an artificial phosphoketolase (APK) pathway, which consists of only 3 types of biochemical reactions. The core enzyme in this pathway is phosphoketolase, while phosphatase and isomerase act as auxiliary enzymes. The APK pathway has the potential to achieve a 100% carbon yield to acetyl-CoA from any monosaccharide by integrating a one-carbon condensation reaction. We tested the APK pathway in vitro, demonstrating that it could efficiently catabolize typical C1-C6 carbohydrates to acetyl-CoA with yields ranging from 83% to 95%. Furthermore, we engineered Escherichia coli stain capable of growth utilizing APK pathway when glycerol act as a carbon source. This novel catabolic pathway holds promising route for future biomanufacturing and offering a stoichiometric production platform using multiple carbon sources.

Uncovering the Mechanism of Azepino-Indole Skeleton Formation via Pictet-Spengler Reaction by Strictosidine Synthase: A Quantum Chemical Investigation

Strictosidine synthase (STR) catalyzes the Pictet-Spengler (PS) reaction of tryptamine and secologanin to produce strictosidine. Recent studies demonstrated that the enzyme can also catalyze the reaction of non-natural substrates to form new alkaloid skeletons. For example, the PS condensation of 1H-indole-4-ethanamine with secologanin could be promoted by the STR from Rauvolfia serpentina (RsSTR) to generate a rare class of skeletons with a seven-membered ring, namely azepino-[3,4,5-cd]-indoles, which are precursors for the synthesis of new compounds displaying antimalarial activity. In the present study, the detailed reaction mechanism of RsSTR-catalyzed formation of the rare seven-membered azepino-indole skeleton through the PS reaction was revealed at the atomic level by quantum chemical calculations. The structures of the transition states and intermediates involved in the reaction pathway were optimized, and the energetics of the complete reaction were analyzed. Based on our calculation results, the most likely pathway of the enzyme-catalyzed reaction was determined, and the rate-determining step of the reaction was clarified. The mechanistic details obtained in the present study are important in understanding the promiscuous activity of RsSTR in the formation of the rare azepino-indole skeleton molecule and are also helpful in designing STR enzymes for the synthesis of other new alkaloid skeleton molecules.

The Quantum Chemical Cluster Approach in Biocatalysis

ConspectusThe quantum chemical cluster approach has been used for modeling enzyme active sites and reaction mechanisms for more than two decades. In this methodology, a relatively small part of the enzyme around the active site is selected as a model, and quantum chemical methods, typically density functional theory, are used to calculate energies and other properties. The surrounding enzyme is modeled using implicit solvation and atom fixing techniques. Over the years, a large number of enzyme mechanisms have been solved using this method. The models have gradually become larger as a result of the faster computers, and new kinds of questions have been addressed. In this Account, we review how the cluster approach can be utilized in the field of biocatalysis. Examples from our recent work are chosen to illustrate various aspects of the methodology. The use of the cluster model to explore substrate binding is discussed first. It is emphasized that a comprehensive search is necessary in order to identify the lowest-energy binding mode(s). It is also argued that the best binding mode might not be the productive one, and the full reactions for a number of enzyme-substrate complexes have therefore to be considered to find the lowest-energy reaction pathway. Next, examples are given of how the cluster approach can help in the elucidation of detailed reaction mechanisms of biocatalytically interesting enzymes, and how this knowledge can be exploited to develop enzymes with new functions or to understand the reasons for lack of activity toward non-natural substrates. The enzymes discussed in this context are phenolic acid decarboxylase and metal-dependent decarboxylases from the amidohydrolase superfamily. Next, the application of the cluster approach in the investigation of enzymatic enantioselectivity is discussed. The reaction of strictosidine synthase is selected as a case study, where the cluster calculations could reproduce and rationalize the selectivities of both the natural and non-natural substrates. Finally, we discuss how the cluster approach can be used to guide the rational design of enzyme variants with improved activity and selectivity. Acyl transferase from Mycobacterium smegmatis serves as an instructive example here, for which the calculations could pinpoint the factors controlling the reaction specificity and enantioselectivity. The cases discussed in this Account highlight thus the value of the cluster approach as a tool in biocatalysis. It complements experiments and other computational techniques in this field and provides insights that can be used to understand existing enzymes and to develop new variants with tailored properties.

[Artificial bioconversion of carbon dioxide]

Utilization of carbon dioxide (CO2) is a huge challenge for global sustainable development. Biological carbon fixation occurs in nature, but the low energy efficiency and slow speed hamper its commercialization. Physical-chemical carbon fixation is efficient, but relies on high energy consumption and often generates unwanted by-products. Combining the advantages of biological, physical and chemical technologies for efficient utilization of CO2 remains to be an urgent scientific and technological challenge to be addressed. Here, based on the development of Tianjin Institute of Industrial Biotechnology, Chinese Academy of Sciences in the past decade, we summarize the important progress in the design and construction of functional parts, pathways and systems for artificial bioconversion of carbon dioxide, including the breakthrough on the artificial synthesis of starch from CO2. Moreover, we prospect how to further develop the technologies for artificial bioconversion of carbon dioxide. These progress and perspectives provide new insight for achieving the goal of "carbon peaking and carbon neutrality".

Sequential left ventricular electro-mechanical changes in left bundle branch pacing vs right ventricular pacing a two-center study

Background

Left bundle branch pacing (LBBP) has been proved to maintain electrical synchrony better than RVP during mid to long-term follow-up, but little is known about the left ventricular (LV) mechanical changes over time. This study investigates if LBBP causes less sequential electro-mechanical alterations in LV that develop over time, compared with both conventional (CRVP) and leadless (LRVP) RVP.

Methods

Sixty-five patients with pacing indication for bradycardia were prospectively enrolled: Twenty-two were treated with LBBP, 23 with CRVP and 20 with LRVP. QRS duration (QRSd) was measured at baseline and during follow-up. All patients underwent echocardiography at baseline, one week after implantation and at one-year follow-up. LV volumes, ejection fraction (EF) and global longitudinal strain (GLS) were measured. Septal flash (SF), apical rocking and septal longitudinal strain patterns were assessed visually by two experienced readers.

Results

All the patients presented with normal strain pattern and no signs of SF or apical rocking at baseline. 100% of CRVP and 95% of LRVP patients had stage1 or 2 septal deformation patterns at week 1, and the majority (72.3% CRVP and 83.3% LRVP) progressed to stage≥2 at 12 months. On the contrary, over 2/3 of LBBP patients preserved normal strain patterns at week 1, and less than 1/3 had stage-1 pattern, 2 out of whom progressed to stage-2 during follow-up (Figure 1). At week 1 and 12 months, all RVP patients had SF, and most of them also exhibited apical rocking (87%-94.4% in CRVP and 80%-94.4% in LRVP). However, much less septal flash and apical rocking was induced in LBBP patients at week 1 and last follow-up (27.3%-37.5% and 22.7%-25%, P<0.001 vs RVP). Baseline QRSd were similar among three groups. At week 1, the paced QRSd increased least in LBBP compared to CRVP and LRVP and remained as such at 12 months. During one year follow-up, LVEF and LV GLS decreased more in CRVP group compared to LBBP (both P<0.05) (Figure 2).

Conclusion

LBBP causes less sequential changes in LV deformation patterns, septal flash and apical rocking, compared to CRVP and LRVP. With this, LBBP appears to preserve LV function better than RVP. CRVP and LRVP did not differ in electro-mechanical changes or LV remodeling.

Funding Acknowledgement

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Research Foundation Flanders (FWO) project grant

Left bundle branch pacing is superior in preserving ventricular mechanical synchrony and cardiac function than right ventricular pacing: a two-center experience

Background

Left bundle branch pacing (LBBP) has emerged as a novel pacing modality. Although it has been proved to maintain electrical synchrony better than right ventricular pacing (RVP), little is known about the impact on mechanical synchrony. This study investigates if LBBP preserves mechanical synchrony and cardiac function better compared to conventional (CRVP) and leadless (LRVP) RVP.

Methods

Sixty-five patients with pacing indication for bradycardia were prospectively enrolled: Twenty-two were treated with LBBP, 23 with CRVP and 20 with LRVP. All patients underwent echocardiography before and after implantation and at one-year follow-up. Left ventricular (LV) volumes, ejection fraction (EF) and global longitudinal strain (GLS) were measured. Regional septal (SW) and lateral wall work (LW) was calculated as the average from the respective basal and mid-ventricular segments in the apical four-chamber and three-chamber view. The lateral-septal work difference (LSWD) was used as a measure of mechanical dyssynchrony.

Results

At baseline, the QRS duration and LSWD were similar in all three groups. During follow-up, the QRS duration increased least in LBBP compared to CRVP and LRVP (+28.1±18.3ms vs +58.2±31.4 and 47.1±26.1ms, both P<0.01). SW was markedly decreased in CRVP and LRVP while LW work remained unchanged, resulting in a large LSWD compared to LBBP (1308.4±732.9 mmHg*% and 1451.3±606.1 mmHg*% vs. 286.0±479.9mmHg*%, both P<0.001). During one year follow-up, LVEF and LV GLS decreased more in CRVP compared to LBBP (both P<0.05).

Conclusion

LBBP causes less LV dyssynchrony than CRVP and LRVP as it preserves a more physiologic conduction pattern. With this, LBBP appears to preserve LV function better than CRVP. CRVP and LRVP did not differ in mechanical dyssynchrony or LV remodelling.

Funding Acknowledgement

Type of funding sources: None.

High glucose inhibits the survival of HRMCs and its mechanism

OBJECTIVE

High glucose can promote the apoptosis of glomerular mesangial cells and cause diabetic nephropathy (DN). However, the mechanism remains unclear. In the present study, we investigated the effects of high glucose on the survival of human renal mesangial cells (HRMCs).

MATERIALS AND METHODS

Cells were treated with high glucose (30 mM) or normal glucose (5 mM) for 48 hours. Cell proliferation was determined by trypan blue assay. The relative expression of metalloproteinase-3 (TIMP3) and inflammatory factors detected by real-time polymerase chain reaction (PCR). Protein expression of Smad2/3, p-Smad2/3 and Smad7 in HRMCs were analyzed by Western blot.

RESULTS

Compared with normal glucose, we found that high glucose significantly inhibited cell survival, accompanied by the decrease of tissue metalloproteinase-3 (TIMP3) mRNA expression. Western blot results showed that the expression of p-Smad2/3 was significantly up-regulated, the expression of Smad7 was significantly downregulated, and inflammatory factors IL-6/IL-8 mRNA expression were increased in the HRMCs cultured with the high glucose. We also found that, compared with the normal glucose, the level of MDA was significantly increased (p<0.01), and the level of SOD was significantly lower (p<0.05) in the HRMCs cultured with the high glucose.

CONCLUSIONS

These findings suggested that high glucose inhibited the survival of HRMCs and may be associated with the downregulation of TIMP3 expression, Smad signaling pathway, inflammation and oxidative stress.

Relationship of resting heart rate and blood pressure with all-cause and cardiovascular disease mortality

OBJECTIVES

This study aimed to investigate associations of resting heart rate (RHR) and blood pressure (BP) with all-cause and cardiovascular disease (CVD) mortality.

STUDY DESIGN

A retrospective cohort study.

METHODS

A total of 67,028 Chinese participants aged ≥60 years were included in the analysis. RHR, systolic blood pressure (SBP), and diastolic blood pressure (DBP) were evaluated according to quartiles ([41-69, 70-74, 75-79, 80-127 beats/min], [80-119, 120-129, 130-139, 140-238 mm Hg], and [40-70, 71-79, 80-84, 85-133 mm Hg]). Cox proportional hazard models were used to estimate the hazard ratios (HRs) and 95% confidence intervals (CIs) of all-cause and CVD mortality with RHR, SBP, and DBP. Restricted cubic splines were used to evaluate the dose-response association.

RESULTS

During the 361,975 person-year follow-up, 9326 deaths were recorded, of which 5039 deaths were due to CVD. The risk of all-cause mortality was increased by 25% with the quartiles four vs quartile one of RHR (HR [95% CI]:1.25 [1.17-1.33]), and CVD mortality was increased by 32% (HR [95% CI]: 1.32 [1.22-1.44]). Similar results were observed when comparing the quartiles four vs quartile one of SBP with the risk of all-cause and CVD mortality (HRs [95% CIs]: 1.14 [1.07, 1.22] and 1.23 [1.12. 1.34]) and DBP with the risk of all-cause and CVD mortality (HRs [95% CIs]: 1.17 [1.11. 1.24] and 1.36 [1.26. 1.47]). We found linear associations of RHR, SBP, and DBP with all-cause and CVD mortality (P_{non-linearity} >0.05), except for the approximately J-shaped association between DBP and all-cause mortality (P_{non-linearity} = 0.008). There was a significant interaction of RHR and SBP with all-cause and CVD mortality (P_interaction <0.05).

CONCLUSIONS

RHR and BP increased the risk of all-cause and CVD mortality, especially fast RHR combined with high SBP.

A Biocatalytic Platform for the Synthesis of Enantiopure Propargylic Alcohols and Amines

Propargylic alcohols and amines are versatile building blocks in organic synthesis. We demonstrate a straightforward enzymatic cascade to synthesize enantiomerically pure propargylic alcohols and amines from readily available racemic starting materials. In the first step, the peroxygenase from Agrocybe aegerita converted the racemic propargylic alcohols into the corresponding ketones, which then were converted into the enantiomerically pure alcohols using the (R)-selective alcohol dehydrogenase from Lactobacillus kefir or the (S)-selective alcohol dehydrogenase from Thermoanaerobacter brokii. Moreover, an enzymatic Mitsunobu-type conversion of the racemic alcohols into enantiomerically enriched propargylic amines using (R)-selective amine transaminase from Aspergillus terreus or (S)-selective amine transaminase from Chromobacterium violaceum was established. The one-pot two-step cascade reaction yielded a broad range of enantioenriched alcohol and amine products in 70–99% yield.

Peroxygenase-Catalyzed Selective Synthesis of Calcitriol Starting from Alfacalcidol

Calcitriol is an active analog of vitamin D3 and has excellent physiological activities in regulating healthy immune function. To synthesize the calcitriol compound, the concept of total synthesis is often adopted, which typically involves multiple steps and results in an overall low yield. Herein, we envisioned an enzymatic approach for the synthesis of calcitriol. Peroxygenase from Agrocybe aegerita (AaeUPO) was used as a catalyst to hydroxylate the C-H bond at the C-25 position of alfacalcidol and yielded the calcitriol in a single step. The enzymatic reaction yielded 80.3% product formation in excellent selectivity, with a turnover number up to 4000. In a semi-preparative scale synthesis, 72% isolated yield was obtained. It was also found that AaeUPO is capable of hydroxylating the C-H bond at the C-1 position of vitamin D3, thereby enabling the calcitriol synthesis directly from vitamin D3.

Left bundle branch pacing preserves ventricular mechanical synchrony better than right ventricular pacing-a two-center study

Funding Acknowledgements

Type of funding sources: None.

Background

Left bundle branch pacing (LBBP) has emerged as a novel pacing method. We sought to evaluate left ventricular (LV) mechanical synchrony under permanent LBBP and compare it with conventional and leadless right ventricular pacing (CRVP, LRVP).

Methods

Sixty-four patients with pacing indication for bradycardia were prospectively enrolled. Twenty-two patients received LBBP in the basal ventricular septum. Twenty-three patients received CRVP and 19 LRVP. All patients underwent echocardiography before and after device implantation. Myocardial work was estimated by pressure-strain analysis. Regional work in the septum (SEP) and lateral wall (LW) was calculated as the average from the respective basal and mid-ventricular segments in the apical four-chamber and three-chamber view. The absolute difference between work in LW and SEP (LW-S-work difference) was used as a measure of asymmetry in workload.

Results

Baseline characteristics were similar among the three groups. The electrocardiogram during LBBP showed a right bundle branch block pattern; during CRVP and LRVP a left bundle branch block pattern. The paced QRS duration was 114.27±9.9 ms in the LBBP group, significantly shorter than that in the CRVP and LRVP groups (153.9±25.26 ms and 159.1±13.99ms, respectively, both p&lt;0.001). The SEP work decreased in all groups during ventricular pacing (all P&lt;0.05), while the LW work remained similar. The paced LW-S work difference and work difference change between pacing on and off were more significant in the CRVP (1012.9±566.0mmHg*%) and LRVP group (1066.1±472.6mmHg*%) than the LBBP group (260.5±239.8mmHg*%, both P&lt;0.001). In addition, LW-S work difference during ventricular pacing and work difference change between pacing and baseline were comparable in CRVP and LRVP group.

Conclusion

LBBP causes less LV dyssynchrony than CRVP and LRVP as it preserves a more physiologic conduction pattern. CRVP and LRVP did not differ in this respect. Further studies need to prove that LBBP has advantages over RVP with regards to preservation of LV synchrony and contractility.

In vitro assessment of the DNA damage and senility of CD117+ stem cells collected from diabetic mice

OBJECTIVE

Angiogenesis impairment is a common feature of diabetes mellitus (DM), whereas CD117+ bone marrow cells (BMCs) injury might be responsible for such complication. In this study, we studied the effect of hyperglycemia on the DNA damage and senility of CD117+ bone marrow cells.

MATERIALS AND METHODS

We isolated CD117+ BMCs from the Streptozotocin (STZ) induced diabetes and healthy control mice. Oxidative stress was detected by flow cytometric analysis. γ-H2AX, which is the DNA damage mark, was detected by using Western blotting and immunofluorescence histochemistry. We also detected the expression of γ-H2AX and p16 by using Western blotting.

RESULTS

Compared with the control mice, the level of reactive oxygen species (ROS) was increased significantly in the CD117+ BMCs collected from the diabetic mice (p<0.05), and the percentage of γ-H2AX positive cells was higher significantly (p<0.01). The expression of γ-H2AX and p16 was increased significantly in the CD117+ BMCs from the diabetic mice.

CONCLUSIONS

Our experiments demonstrated the oxidative stress in CD117+ BMCs under DM conditions, while accelerating the DNA damage and senility in CD117+ BMCs as well.

β-Methyltryptamine Provoking the Crucial Role of Strictosidine Synthase Tyr151-OH for Its Stereoselective Pictet-Spengler Reactions to Tryptoline-type Alkaloids

Strictosidine synthase (STR), the gate enzyme for monoterpenoid indole alkaloid biosynthesis, catalyzes the Pictet-Spengler reaction (PSR) of various tryptamine derivatives with secologanin assisted by "indole sandwich" stabilization. Continuous exploration with β-methyltryptamine (IPA) stereoselectively delivered the C6-methylstrictosidines and C6-methylvincosides by enzymatic and nonenzymatic PSR, respectively. Unexpectedly, the first "nonindole sandwich" binding mode was witnessed by the X-ray structures of STR1-ligand complexes. Site-directed mutagenesis revealed the critical cryptic role of the hydroxyl group of Tyr151 in IPA biotransformation. Further computational calculations demonstrated the adjustable IPA position in STR1 upon the binding of secologanin, and Tyr151-OH facilitates the productive PSR binding mode via an advantageous hydrogen-bond network. Further chemo-enzymatic manipulation of C6-methylvincosides successfully resulted in the discovered antimalarial framework (IC50 = 0.92 μM).

Unraveling the mechanism of enantio-controlling switches of an alcohol dehydrogenase toward sterically small ketone

Efficient synthesis of chiral compounds under mild conditions is highly desirable in the chemical and pharmaceutical communities, but it often faces difficulties. Although various enzymes have been harnessed as biocatalysts...

Stability of a Novel PEGylation Site on a Putative Haemoglobin-Based Oxygen Carrier

PEGylation of protein sulfhydryl residues is a common method used to create a stable drug conjugate to enhance vascular retention times. We recently created a putative haemoglobin-based oxygen carrier using maleimide-PEG to selectively modify a single engineered cysteine residue in the α subunit (αAla19Cys). However, maleimide-PEG adducts are subject to deconjugation via retro-Michael reactions, with consequent cross-conjugation to endogenous plasma thiols such as those found on human serum albumin or glutathione. In previous studies mono-sulfone-PEG adducts have been shown to be less susceptible to deconjugation. We therefore compared the stability of our maleimide-PEG Hb adduct with one created using a mono-sulfone PEG. The corresponding mono-sulfone-PEG adduct was significantly more stable when incubated at 37 °C for 7 days in the presence of 1 mM reduced glutathione, 20 mg/mL human serum albumin, or human serum. In all cases haemoglobin treated with mono-sulfone-PEG retained >90% of its conjugation whereas maleimide-PEG showed significant deconjugation, especially in the presence of 1 mM reduced glutathione where <70% of the maleimide-PEG conjugate remained intact. Although maleimide-PEGylation of Hb seems adequate for an oxygen therapeutic intended for acute use, if longer vascular retention is required reagents such as mono-sulfone-PEG may be more appropriate.

Computational Study of Mechanism and Enantioselectivity of Imine Reductase from Amycolatopsis orientalis

Imine reductases (IREDs) are NADPH-dependent enzymes (NADPH=nicotinamide adenine dinucleotide phosphate) that catalyze the reduction of imines to amines. They exhibit high enantioselectivity for a broad range of substrates, making them of interest for biocatalytic applications. In this work, we have employed density functional theory (DFT) calculations to elucidate the reaction mechanism and the origins of enantioselectivity of IRED from Amycolatopsis orientalis. Two substrates are considered, namely 1-methyl-3,4-dihydroisoquinoline and 2-propyl-piperideine. A model of the active site is built on the basis of the available crystal structure. For both substrates, different binding modes are first evaluated, followed by calculation of the hydride transfer transition states from each complex. We have also investigated the effect of mutations of certain important active site residues (Tyr179Ala and Asn241Ala) on the enantioselectivity. The calculated energies are consistent with the experimental observations and the analysis of transition states geometries provides insights into the origins of enantioselectivity of this enzyme.

Mechanisms of metal-dependent non-redox decarboxylases from quantum chemical calculations

Quantum chemical calculations are today an extremely valuable tool for studying enzymatic reaction mechanisms. In this mini-review, we summarize our recent work on several metal-dependent decarboxylases, where we used the so-called cluster approach to decipher the details of the reaction mechanisms, including elucidation of the identity of the metal cofactors and the origins of substrate specificity.

Decarboxylases are of growing potential for biocatalytic applications, as they can be used in the synthesis of novel compounds of, e.g., pharmaceutical interest. They can also be employed in the reverse direction, providing a strategy to synthesize value‐added chemicals by CO₂ fixation. A number of non-redox metal-dependent decarboxylases from the amidohydrolase superfamily have been demonstrated to have promiscuous carboxylation activities and have attracted great attention in the recent years. The computational mechanistic studies provide insights that are important for the further modification and utilization of these enzymes in industrial processes. The discussed enzymes are: 5‐carboxyvanillate decarboxylase, γ‐resorcylate decarboxylase, 2,3‐dihydroxybenzoic acid decarboxylase, and iso-orotate decarboxylase.

Crystal Structures and Catalytic Mechanism of l-erythro-3,5-Diaminohexanoate Dehydrogenase and Rational Engineering for Asymmetric Synthesis of β-Amino Acids

Amino acid dehydrogenases (AADHs) have shown considerable potential as biocatalysts in the asymmetric synthesis of chiral amino acids. However, compared to the widely studied α-AADHs, limited knowledge is available about β-AADHs that enable the synthesis of β-amino acids. Herein, we report the crystal structures of a l-erythro-3,5-diaminohexanoate dehydrogenase and its variants, the only known member of β-AADH family. Crystal structure analysis, site-directed mutagenesis studies and quantum chemical calculations revealed the differences in the substrate binding and catalytic mechanism from α-AADHs. A number of rationally engineered variants were then obtained with improved activity (by 110-800 times) toward various aliphatic β-amino acids without an enantioselectivity trade-off. Two β-amino acids were prepared by using the outstanding variants with excellent enantioselectivity (>99 % ee) and high isolated yields (86-87 %). These results provide important insights into the molecular mechanism of 3,5-DAHDH, and establish a solid foundation for further design of β-AADHs for the asymmetric synthesis of β-amino acids.

Metal Ion Promiscuity and Structure of 2,3-Dihydroxybenzoic Acid Decarboxylase of Aspergillus oryzae

Broad substrate tolerance and excellent regioselectivity, as well as independence from sensitive cofactors have established benzoic acid decarboxylases from microbial sources as efficient biocatalysts. Robustness under process conditions makes them particularly attractive for preparative-scale applications. The divalent metal-dependent enzymes are capable of catalyzing the reversible non-oxidative (de)carboxylation of a variety of electron-rich (hetero)aromatic substrates analogously to the chemical Kolbe-Schmitt reaction. Elemental mass spectrometry supported by crystal structure elucidation and quantum chemical calculations verified the presence of a catalytically relevant Mg2+ complexed in the active site of 2,3-dihydroxybenoic acid decarboxylase from Aspergillus oryzae (2,3-DHBD_Ao). This unique example with respect to the nature of the metal is in contrast to mechanistically related decarboxylases, which generally have Zn2+ or Mn2+ as the catalytically active metal.

Mechanism of 3-Methylglutaconyl CoA Decarboxylase AibA/AibB: Pericyclic Reaction versus Direct Decarboxylation

The enzyme 3-methylglutaconyl coenzyme A (CoA) decarboxylase (called AibA/AibB) catalyzes the decarboxylation of 3-methylglutaconyl CoA to generate 3,3-dimethylacrylyl-CoA, representing an important step in the biosynthesis of isovaleryl-coenzyme A in Myxococcus xanthus when the regular pathway is blocked. A novel mechanism involving a pericyclic transition state has previously been proposed for this enzyme, making AibA/AibB unique among decarboxylases. Herein, density functional calculations are used to examine the energetic feasibility of this mechanism. It is shown that the intramolecular pericyclic reaction is associated with a very high energy barrier that is similar to the barrier of the same reaction in the absence of the enzyme. Instead, the calculations show that a direct decarboxylation mechanism has feasible energy barriers that are in line with the experimental observations.

A Priori Sample Size Determination for the Number of Subjects in an EEG Experiment

This paper represents a first attempt to perform a priori sample size determination from a "historic" Electroencephalography (EEG) dataset. The importance of adequate sample size is firstly highlighted, and evidence is given against the use of normal distribution for such computations, when the data cannot be assumed to be Gaussian. The "historic" dataset is then thoroughly examined to determine the least less likely underlying distribution for the desired phenomenon, in this case the spontaneous blinks potential. Two Monte Carlo simulations, using different distribution assumptions, are subsequently computed to estimate the a priori minimum sample size. Finally, these choices are discussed considering practical limitations, as well as the computational differences for other phenomena to study.

Mechanism of Biocatalytic Friedel-Crafts Acylation by Acyltransferase from Pseudomonas protegens

Acyltransferases isolated from Pseudomonas protegens (PpATase) and Pseudomonas fluorescens (PfATase) have recently been reported to catalyze the Friedel–Crafts acylation, providing a biological version of this classical organic reaction. These enzymes catalyze the cofactor-independent acylation of monoacetylphloroglucinol (MAPG) to diacetylphloroglucinol (DAPG) and phloroglucinol (PG) and have been demonstrated to have a wide substrate scope, making them valuable for potential applications in biocatalysis. Herein, we present a detailed reaction mechanism of PpATase on the basis of quantum chemical calculations, employing a large model of the active site. The proposed mechanism is consistent with available kinetics, mutagenesis, and structural data. The roles of various active site residues are analyzed. Very importantly, the Asp137 residue, located more than 10 Å from the substrate, is predicted to be the proton source for the protonation of the substrate in the rate-determining step. This key prediction is corroborated by site-directed mutagenesis experiments. Based on the current calculations, the regioselectivity of PpATase and its specificity toward non-natural substrates can be rationalized.

Validation of the Investigator 24plex QS Kit: a 6-dye multiplex PCR assay for forensic application in the Chinese Han population

The Investigator 24plex QS Kit (QIAGEN, Hilden, Germany) is a 6-dye fluorescent chemistry short tandem repeat (STR) polymerase chain reaction (PCR) amplification system that simultaneously amplifies 20 of the expanded Combined DNA Index System (CODIS) core STR loci, SE33, DYS391, and the standard sex-determining locus, amelogenin, as well as two special internal performance quality sensor controls (QS1 and QS2), which are included in the primer mix to check the PCR performance. This study was designed to be a pilot evaluation of this STR-PCR kit in a Chinese Han population regarding the PCR conditions, sensitivity, precision, accuracy, repeatability, reproducibility, and concordance; tolerance to PCR inhibitors; applicability to real “forensic-type” samples; species specificity; mixture, balance and stutter analyses, and utility in a population investigation. The exhaustive validation studies demonstrated that the Investigator 24plex QS system is accurate, sensitive and robust for STR genotyping. In addition, these genetic markers in the population data in our study indicated that they can also be useful for forensic identification and paternity testing in the Chinese Han population.