Xylan oligosaccharides and cellobiohydrolase I (TrCel7A) interaction and effect on activity

<p>Abstract</p> <p>Background</p> <p>The well-studied cellulase mixture secreted by <it>Trichoderma reesei </it>(anamorph to <it>Hypocrea jecorina</it>) contains two cellobiohydolases (CBHs), cellobiohydrolase I (<it>Tr</it>Cel7A) and cellobiohydrolase II (<it>Tr</it>CeI6A), that are core enzymes for the solubilisation of cellulose. This has attracted significant research interest because of the role of the CBHs in the conversion of biomass to fermentable sugars. However, the CHBs are notoriously slow and susceptible to inhibition, which presents a challenge for the commercial utilisation of biomass. The xylans and xylan fragments that are also present in the biomass have been suggested repeatedly as one cause of the reduced activity of CHBs. Yet, the extent and mechanisms of this inhibition remain poorly elucidated. Therefore, we studied xylan oligosaccharides (XOSs) of variable lengths with respect to their binding and inhibition of both <it>Tr</it>Cel7A and an enzyme variant without the cellulose-binding domain (CBM).</p> <p>Results</p> <p>We studied the binding of XOSs to <it>Tr</it>Cel7A by isothermal titration calorimetry. We found that XOSs bind to <it>Tr</it>Cel7A and that the affinity increases commensurate with XOS length. The CBM, on the other hand, did not affect the affinity significantly, which suggests that XOSs may bind to the active site. Activity assays of <it>Tr</it>Cel7A clearly demonstrated the negative effect of the presence of XOSs on the turnover number.</p> <p>Conclusions</p> <p>On the basis of these binding data and a comparison of XOS inhibition of the activity of the two enzyme variants towards, respectively, soluble and insoluble substrates, we propose a competitive mechanism for XOS inhibition of <it>Tr</it>Cel7A with phosphoric swollen cellulose as a substrate.</p

Evolution of the Dark Matter Distribution with 3-D Weak Lensing

We present a direct detection of the growth of large-scale structure, using weak gravitational lensing and photometric redshift data from the COMBO-17 survey. We use deep R-band imaging of two 0.25 square degree fields, affording shear estimates for over 52000 galaxies; we combine these with photometric redshift estimates from our 17 band survey, in order to obtain a 3-D shear field. We find theoretical models for evolving matter power spectra and correlation functions, and fit the corresponding shear correlation functions to the data as a function of redshift. We detect the evolution of the power at the 7.7 sigma level given minimal priors, and measure the rate of evolution for 0<z<1. We also fit correlation functions to our 3-D data as a function of cosmological parameters sigma_8 and Omega_Lambda. We find joint constraints on Omega_Lambda and sigma_8, demonstrating an improvement in accuracy by a factor of 2 over that available from 2D weak lensing for the same area.Comment: 11 pages, 4 figures; submitted to MNRA

Star Formation and the Growth of Stellar Mass

Recent observations have demonstrated a significant growth in the integrated stellar mass of the red sequence since z=1, dominated by a steadily increasing number of galaxies with stellar masses M* < 10^11 M_sun. In this paper, we use the COMBO-17 photometric redshift survey in conjunction with deep Spitzer 24 micron data to explore the relationship between star formation and the growth of stellar mass. We calculate `star formation rate functions' in four different redshift slices, splitting also into contributions from the red sequence and blue cloud for the first time. We find that the growth of stellar mass since z=1 is consistent with the integrated star formation rate. Yet, most of the stars formed are in blue cloud galaxies. If the stellar mass already in, and formed in, z<1 blue cloud galaxies were to stay in the blue cloud the total stellar mass in blue galaxies would be dramatically overproduced. We explore the expected evolution of stellar mass functions, finding that in this picture the number of massive M* > 3x10^10 M_sun blue galaxies would also be overproduced; i.e., most of the new stars formed in blue cloud galaxies are in the massive galaxies. We explore a simple truncation scenario in which these `extra' blue galaxies have their star formation suppressed by an unspecified mechanism or mechanisms; simple cessation of star formation in these extra blue galaxies is approximately sufficient to build up the red sequence at M*<10^11 M_sun.Comment: 9 Pages; ApJ in pres

Binding prediction of multi-domain cellulases with a dual-CNN

Cellulases hold great promise for the production of biofuels and biochemicals. However, they are modular enzymes acting on a complex heterogeneous substrate. Because of this complexity, the computational prediction of their catalytic properties remains scarce, which restricts both enzyme discovery and enzyme design. Here, we present a dual-input convolutional neural network to predict the binding of multi-domain enzymes. This regression model outperformed previous molecular dynamics-based methods for binding prediction for cellulases in a fraction of the time. Also, we show that when changed to a classification problem, the same network can be back-propagated to suggest mutations to improve enzyme binding. A similar approach could increase our understanding of the structure-activity relationship of enzymes, and suggest new promising mutations for enzyme design using explainable artificial intelligence

Natural History of Insulin Sensitivity and Insulin Secretion in the Progression From Normal Glucose Tolerance to Impaired Fasting Glycemia and Impaired Glucose Tolerance: The Inter99 Study

OBJECTIVE—The aim of this study was to describe the natural history of insulin secretion and insulin sensitivity in the development of isolated impaired fasting glycemia (i-IFG), isolated impaired glucose tolerance (i-IGT), and combined IFG/IGT

Beretning om Mejemaskinprøven 1874 paa Benzonsdal og Vallensbæk Jorder, foranstaltet af det kgl. Landhusholdningsselskab.

Beretning om Mejemaskinprøven 1874 paa Benzonsdal og Vallensbæk Jorder, foranstaltet af det kgl. Landhusholdningsselskab

Max-Min optimization problem for Variable Annuities pricing

International audienceWe study the valuation of variable annuities for an insurer. We concentrate on two types of these contracts that are the guaranteed minimum death benefits and the guaranteed minimum living benefits ones and that allow the insured to withdraw money from the associated account. As for many insurance contracts, the price of variable annuities consists in a fee, fixed at the beginning of the contract, that is continuously taken from the associated account. We use a utility indifference approach to determine this fee and, in particular, we consider the indifference fee rate in the worst case for the insurer i.e. when the insured makes the withdrawals that minimize the expected utility of the insurer. To compute this indifference fee rate, we link the utility maximization in the worst case for the insurer to a sequence of maximization and minimization problems that can be computed recursively. This allows to provide an optimal investment strategy for the insurer when the insured follows the worst withdrawals strategy and to compute the indifference fee. We finally explain how to approximate these quantities via the previous results and give numerical illustrations of parameter sensibility

Evolution of optically faint AGN from COMBO-17 and GEMS

We have mapped the AGN luminosity function and its evolution between z=1 and z=5 down to apparent magnitudes of $R<24$. Within the GEMS project we have analysed HST-ACS images of many AGN in the Extended Chandra Deep Field South, enabling us to assess the evolution of AGN host galaxy properties with cosmic time.Comment: to appear in proceedings 'Multiwavelength AGN Surveys', Cozumel 200