Dissociation of CH₃–O as a Driving Force for Methoxyacetophenone Adsorption on Si(001)

The coverage-dependent behavior of p-methoxyacetophenone on the clean Si(001) surface was followed using X-ray photoelectron spectroscopy and supporting density functional theory calculations. Unlike other multifunctional organic molecules, this compound exhibits a high selectivity of adsorbate species formation by forming only two distinct adsorbate structures at low coverage, with a third configuration forming at high coverages. At low coverage, surface chemisorption is driven by methoxy group dissociation. However, at high coverage, the surface footprint required for this process is no longer available, leading to the formation of less thermodynamically stable adsorbates that are datively bonded to the surface with a smaller footprint. This coverage-dependent but well-defined behavior is promising in designing functional organic–inorganic interfaces on silicon

Recombining Low Homology, Functionally Rich Regions of Bacterial Subtilisins by Combinatorial Fragment Exchange

Combinatorial fragment exchange was utilised to recombine key structural and functional low homology regions of bacilli subtilisins to generate new active hybrid proteases with altered substrate profiles. Up to six different regions comprising mostly of loop residues from the commercially important subtilisin Savinase were exchanged with the structurally equivalent regions of six other subtilisins. The six additional subtilisins derive from diverse origins and included thermophilic and intracellular subtilisins as well as other academically and commercially relevant subtilisins. Savinase was largely tolerant to fragment exchange; rational replacement of all six regions with 5 of 6 donating subtilisin sequences preserved activity, albeit reduced compared to Savinase. A combinatorial approach was used to generate hybrid Savinase variants in which the sequences derived from all seven subtilisins at each region were recombined to generate new region combinations. Variants with different substrate profiles and with greater apparent activity compared to Savinase and the rational fragment exchange variants were generated with the substrate profile exhibited by variants dependent on the sequence combination at each region

EFFECTS OF EGLIN-C BINDING TO THERMITASE - 3-DIMENSIONAL STRUCTURE COMPARISON OF NATIVE THERMITASE AND THERMITASE EGLIN-C COMPLEXES

Thermitase is a thermostable member of the subtilisin family of serine proteases. Four independently determined crystal structures of the enzyme are compared in this study: a high resolution native one and three medium resolution complexes of thermitase with eglin-c, grown from three different calcium concentrations. It appeared that the B-factors of the thermitase eglin complex obtained at 100 mM CaCl2 and elucidated at 2.0 A resolution are remarkably similar to those of the 1.4 A native structure: the main chain atoms have an rms difference of only 2.3 A 2; for all atoms this difference is 4.6 A 2. The rms positional differences between these two structures of thermitase are 0.31 A for the main chain atoms and 0.58 A for all atoms. There results show that not only atomic positions but also temperature factors can agree well in X-ray structures determined entirely independently by procedures which differ in virtually every possible technical aspect. A detailed comparison focussed on the effects of eglin binding on the structure of thermitase. Thermitase can be considered as consisting of (1) a central core of 94 residues, plus (2) four segments of 72 residues in total which shift as rigid bodies with respect to the core, plus (3) the remaining 113 residues which show small changes but, however, cannot be described as rigid bodies. The central cores of native thermitase and the 100 mM CaCl2 thermitase:eglin complex have an rims deviation of 0.13 A for 376 main chain atoms. One of the segments, formed by loops of the strong calcium binding site, shows differences up to 1.0 A in C-alpha positions. These are probably due to crystal packing effects. The three other segments, comprising 51 residues, are affected conformational changes upon eglin binding so that the P1 to P3 binding pockets of thermitase broaden by 0.4 to 0.7 A. The residues involved in these changes correspond with residues which change position upon inhibitor binding in other subtilisins. This suggests that an induced fit mechanism is operational during substrate recognition by subtilisins

Effect of long-term therapy with AT1angiotensin II receptor blockers in combination with aldosterone receptor inhibitor on ischemic myocardial remodelling and chronic heart failure

The article presents the results of a 6-month long-term therapy with angiotensin II receptor blocker Valsacor and aldosterone receptor blocker Spironolactone in patients with chronic heart failure (CHF) against a background of ischemic and/or post-infarction left ventricular remodelling. The results show that the renin-angiotensin-aldosterone system (RAAS) blockade in the combination therapy slows down the pathological remodelling of the left ventricle (LV) and thus prevents progression of CHF in a majority of patients with myocardial infarction (MI)

Modeling and structural analysis of PA clan serine proteases

<p>Abstract</p> <p>Background</p> <p>Serine proteases account for over a third of all known proteolytic enzymes; they are involved in a variety of physiological processes and are classified into clans sharing structural homology. The PA clan of endopeptidases is the most abundant and over two thirds of this clan is comprised of the S1 family of serine proteases, which bear the archetypal trypsin fold and have a catalytic triad in the order Histidine, Aspartate, Serine. These proteases have been studied in depth and many three dimensional structures have been experimentally determined. However, these structures mostly consist of bacterial and animal proteases, with a small number of plant and fungal proteases and as yet no structures have been determined for protozoa or archaea. The core structure and active site geometry of these proteases is of interest for many applications. This study investigated the structural properties of different S1 family serine proteases from a diverse range of taxa using molecular modeling techniques.</p> <p>Results</p> <p>Our predicted models from protozoa, archaea, fungi and plants were combined with the experimentally determined structures of 16 S1 family members and used for analysis of the catalytic core. Amino acid sequences were submitted to SWISS-MODEL for homology-based structure prediction or the LOOPP server for threading-based structure prediction. Predicted models were refined using INSIGHT II and SCRWL and validated against experimental structures. Investigation of secondary structures and electrostatic surface potential was performed using MOLMOL. The structural geometry of the catalytic core shows clear deviations between taxa, but the relative positions of the catalytic triad residues were conserved. Some highly conserved residues potentially contributing to the stability of the structural core were identified. Evolutionary divergence was also exhibited by large variation in secondary structure features outside the core, differences in overall amino acid distribution, and unique surface electrostatic potential patterns between species.</p> <p>Conclusions</p> <p>Encompassing a wide range of taxa, our structural analysis provides an evolutionary perspective on S1 family serine proteases. Focusing on the common core containing the catalytic site of the enzyme, this analysis is beneficial for future molecular modeling strategies and structural analysis of serine protease models.</p