Characterization and computation-supported engineering of an ω-transaminase

An (S)-selective homodimeric ω-transaminase from Pseudomonas jessenii (PjTA) that naturally converts 6-aminohexanoic acid to 6-oxohexanoic acid in the caprolactam biodegradation pathway was discovered and characterized in our lab. However, the applications of dimeric ω-transaminases were hindered by enzyme instability and their limited substrate scope. Thus PjTA was selected as the model system and protein engineering was used to improve the enzyme stability and redirect the preference of substrate. A computational method (FRESCO) which was previously explored by our group was applied to stabilize PjTA. Both the extent of stabilization and the spatial distribution of stabilizing mutations showed that the subunit interface was critical for the stability of PjTA. After a rational combination, a robust PjTA was obtained that more active at high temperatures and more tolerant to cosolvents and to a high concentration of amino donor (isopropylamine). Then this robust PjTA was selected to redesign the enzyme binding pockets to improve the production of enantiopure bulky amines from prochiral ketones via asymmetric synthesis. A computational approach with a high success rate was explored and the yields in the synthesis of selected bulky amines were highly improved with >99% enantiomeric excess

Degree-day based non-domestic building energy analytics and modelling should use building and type specific base temperatures

A deeper understanding of building performance is essential to reduce their energy consumption and corresponding greenhouse gas emissions. Heating degree-days (HDD) encapsulates the severity and duration of cold weather, which is routinely used for weather related analysis of fuel consumption, performance benchmarking, and compliance. The accuracy of HDD-based prediction largely depends on the correct base temperature, which varies depending on building thermal characteristics, and their operation and occupancy. We analysed four years’ (2012-2016) half-hourly metered gas consumption from 119 non-domestic buildings representing seven types, to: (a) identify their base temperature using a three-parameter change point (3PH) regression model, and (b) their relationships with intrinsic building parameters. The highest mean base temperature, 17.7°C was found for clubs and community centres, and the lowest, 12.8°C was for storage buildings. The average of all base temperatures is 16.7°C, which is 1.2°C higher and 1.6°C lower than the British (15.5°C) and American (18.3°C) standards respectively. The current practice of a fixed base temperature degree-days for all buildings has been found to be unrealistic. Building type specific base temperatures must be developed, agreed upon and published for increasing accuracy in energy analytics and legislative compliance, as well as for developing effective standards and policies

Going beyond the mean: distributional degree-day base temperatures for building energy analytics using change point quantile regression

Building energy consumption patterns are primarily affected by building function, operation, occupancy and thermal characteristics. A robust method of energy use pattern recognition is, therefore, essential. Heating degree-days (HDD) are routinely used for heating energy consumption prediction and analytics, the accuracy of which depends on how well the base temperature corresponds with the patterns of energy use. A change-point quantile regression (CPQR) technique is proposed for better identification of the base temperature, which is then applied in three buildings with distinct operational energy use patterns: weekday only, weekday plus occasional weekend, and all-year operation. Compared with the conventional regression and change-point least square (CPLS) methods, our CPQR approach determines a range of base temperatures of corresponding energy use patterns across quantiles from 0.05 to 0.95, at an interval of 0.05. Consequently, daily HDDs computed using the range of base temperatures of corresponding quantiles result in more accurate predictions of heating energy consumption. CPQR improves estimation accuracy and is more robust than CPLS because (a) it considers the whole distribution of energy consumption not just the mean, (b) pre-processing of raw data other than the removal of anomalies is not needed, and (c) it can better characterize the data with abnormal energy distribution. Also, CPQR-based method can better characterize the weather dependence of energy consumption than the conventional CPLS regression

catena-Poly[[dianilinedichloridocopper(II)]-μ2-2,5-bis­(4-pyrid­yl)-1,3,4-oxadiazole]

In the title compound, [CuCl2(C6H7N)2(C12H8N4O)]n, the Cu atom, located on an inversion center, is coordinated by four N atoms from two aniline ligands and two 2,5-bis­(4-pyrid­yl)-1,3,4-oxadiazole ligands. Two Cl atoms lying above and below the plane formed by these four N atoms inter­act weakly with the Cu atom [Cu—Cl = 2.7870 (7) Å]. The trans 2,5-bis­(4-pyrid­yl)-1,3,4-oxadiazole ligands act as bridging ligands, linking adjacent Cu atoms and forming a one-dimensional coordination polymer. Two anilines coordinate with each Cu atom as terminal groups. The structure contains two classical N—H⋯Cl and two non-classical C—H⋯Cl hydrogen bonds

Predicting the Number of Future Events

This paper describes prediction methods for the number of future events from a population of units associated with an on-going time-to-event process. Examples include the prediction of warranty returns and the prediction of the number of future product failures that could cause serious threats to property or life. Important decisions such as whether a product recall should be mandated are often based on such predictions. Data, generally right-censored (and sometimes left truncated and right-censored), are used to estimate the parameters of a time-to-event distribution. This distribution can then be used to predict the number of events over future periods of time. Such predictions are sometimes called within-sample predictions and differ from other prediction problems considered in most of the prediction literature. This paper shows that the plug-in (also known as estimative or naive) prediction method is not asymptotically correct (i.e., for large amounts of data, the coverage probability always fails to converge to the nominal confidence level). However, a commonly used prediction calibration method is shown to be asymptotically correct for within-sample predictions, and two alternative predictive-distributionbased methods that perform better than the calibration method are presented and justified

Poly[(μ2-3,6-di-4-pyridyl-1,2,4,5-tetra­zine)(μ2-thio­cyanato)copper(I)]

The title compound, [Cu(NCS)(C12H8N6)]n, is a self-assembled two-dimensional metal–organic network. The Cu atom is linked by two N atoms from two 3,6-di-4-pyridyl-1,2,4,5-tetra­zine ligands and by the N and S atoms from two thio­cyanate ligands in a distorted tetra­hedral environment. The Cu atom and the thio­cyanate ligand occupy a crystallographic mirror plane m, and a crystallographic inversion centre is in the middle of the tetra­zine ring, generating the zigzag fashion of the two-dimensional network. The infinite –Cu—SCN—Cu—SCN– chain is due to translational symmetry along the a axis. These chains are further connected through the 3,6-di-4-pyridyl-1,2,4,5-tetra­zine ligands that bridge the CuI centers, generating a two-dimensional network. There are π—π stacking inter­actions between the pyridine and tetra­zine rings (perpendicular distances of 3.357 and 3.418 Å), with a centroid–centroid distance of 3.6785 (16) Å

Biochemical properties of a Pseudomonas aminotransferase involved in caprolactam metabolism

The biodegradation of the nylon-6 precursor caprolactam by a strain of Pseudomonas jessenii proceeds via ATP-dependent hydrolytic ring-opening to 6-aminohexanoate. This non-natural ω-amino acid is converted to 6-oxohexanoic acid by an aminotransferase (PjAT) belonging to the fold type I PLP enzymes. To understand the structural basis of 6-aminohexanoatate conversion, we solved different crystal structures and determined the substrate scope with a range of aliphatic and aromatic amines. Comparison with the homologous aminotransferases from Chromobacterium violaceum (CvAT) and Vibrio fluvialis (VfAT) showed that the PjAT enzyme has the lowest KM values (highest affinity) and highest specificity constant (kcat /KM ) with the caprolactam degradation intermediates 6-aminohexanoate and 6-oxohexanoic acid, in accordance with its proposed in vivo function. Five distinct three-dimensional structures of PjAT were solved by protein crystallography. The structure of the aldimine intermediate formed from 6-aminohexanoate and the PLP cofactor revealed the presence of a narrow hydrophobic substrate-binding tunnel leading to the cofactor and covered by a flexible arginine, which explains the high activity and selectivity of the PjAT with 6-aminohexanoate. The results suggest that the degradation pathway for caprolactam has recruited an aminotransferase that is well adapted to 6-aminohexanoate degradation. This article is protected by copyright. All rights reserved

Asymmetric synthesis of optically pure aliphatic amines with an engineered robust ω-transaminase

The production of chiral amines by transaminase-catalyzed amination of ketones is an important application of biocatalysis in synthetic chemistry. It requires transaminases that show high enantioselectivity in asymmetric conversion of the ketone precursors. A robust derivative of ω-transaminase from Pseudomonas jessenii (PjTA-R6) that naturally acts on aliphatic substrates was constructed previously by our group. Here, we explore the catalytic potential of this thermostable enzyme for the synthesis of optically pure aliphatic amines and compare it to the well-studied transaminases from Vibrio fluvialis (Vf TA) and Chromobacterium violaceum (CvTA). The product yields indicated improved performance of PjTA-R6 over the other transaminases, and in most cases, the optical purity of the produced amine was above 99% enantiomeric excess (e.e.). Structural analysis revealed that the substrate binding poses were influenced and restricted by the switching arginine and that this accounted for differences in substrate specificities. Rosetta docking calculations with external aldimine structures showed a correlation between docking scores and synthetic yields. The results show that PjTA-R6 is a promising biocatalyst for the asymmetric synthesis of aliphatic amines with a product spectrum that can be explained by its structural features

A demand-response method to balance electric power-grids via HVAC systems using active energy-storage: simulation and on-site experiment

With the increasing popularity of renewable energy sources and the globally increasing electricity demand, the task of balancing the intermittent energy supply with varying demand becomes increasingly difficult. Instead of adjusting the supply, improving the demand response (DR) can be a more efficient way to optimize power balance. HVAC (heating, ventilation, and air-conditioning) systems, which operate on the demand side of power-grids, have a huge potential to improve the power balance. To assess their potential in a variable air volume (VAV) air-conditioning system with energy storage tank we introduce a demand response method that combines active cool-energy storage (ACES) with global temperature adjustment (GTA). To confirm the effectiveness of this combined ACES+GTA approach, we conduct measurements with the help of a full-scale VAV air-conditioning test setup. The experimental results are compared with a TRNSYS simulation. The measurements indicate that an energy-storing water-tank can effectively reduce the number of starts and stops for the heat pump. The simulation confirms that the ACES+GTA method can also effectively reduce the peak load of the power grid with little impact on the thermal comfort of the energy consumers. The cost-saving rate, compared to the conventional operating mode (no energy-storage during other periods), reaches 7.02% for an entire cooling season if the GTA method (with DR) is used