Artificial Metalloenzymes Based on the Biotin–Streptavidin Technology: Challenges and Opportunities

The biotin–streptavidin technology offers an attractive means to engineer artificial metalloenzymes (ArMs). Initiated over 50 years ago by Bayer and Wilchek, the biotin–(strept)avidin techonology relies on the exquisite supramolecular affinity of either avidin or streptavidin for biotin. This versatile tool, commonly referred to as “molecular velcro”, allows nearly irreversible anchoring of biotinylated probes within a (strept)avidin host protein. Building upon a visionary publication by Whitesides from 1978, several groups have been exploiting this technology to create artificial metalloenzymes. For this purpose, a biotinylated organometallic catalyst is introduced within (strept)avidin to afford a hybrid catalyst that combines features reminiscent of both enzymes and organometallic catalysts. Importantly, ArMs can be optimized by chemogenetic means. Combining a small collection of biotinylated organometallic catalysts with streptavidin mutants allows generation of significant diversity, thus allowing optimization of the catalytic performance of ArMs. Pursuing this strategy, the following reactions have been implemented: hydrogenation, alcohol oxidation, sulfoxidation, dihydroxylation, allylic alkylation, transfer hydrogenation, Suzuki cross-coupling, C–H activation, and metathesis. In this Account, we summarize our efforts in the latter four reactions. X-ray analysis of various ArMs based on the biotin–streptavidin technology reveals the versatility and commensurability of the biotin-binding vestibule to accommodate and interact with transition states of the scrutinized organometallic transformations. In particular, streptavidin residues at positions 112 and 121 recurrently lie in close proximity to the biotinylated metal cofactor. This observation led us to develop a streamlined 24-well plate streptavidin production and screening platform to optimize the performance of ArMs. To date, most of the efforts in the field of ArMs have focused on the use of purified protein samples. This seriously limits the throughput of the optimization process. With the ultimate goal of complementing natural enzymes in the context of synthetic and chemical biology, we outline the milestones required to ultimately implement ArMs within a cellular environment. Indeed, we believe that ArMs may allow signficant expansion of the natural enzymes’ toolbox to access new-to-nature reactivities in vivo . With this ambitious goal in mind, we report on our efforts to (i) activate the biotinylated catalyst precursor upon incorporation within streptavidin, (ii) minimize the effect of the cellular environment on the ArM’s performance, and (iii) demonstrate the compatibility of ArMs with natural enzymes in cascade reactions

Adhesion of surfaces mediated by adsorbed particles: Monte Carlo simulations and a general relationship between adsorption isotherms and effective adhesion energies

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.In colloidal and biological systems, interactions between surfaces are often mediated by adsorbed particles or molecules that interconnect the surfaces. In this article, we present a general relationship between the adsorption isotherms of the particles and the effective, particle-mediated adhesion energies of the surfaces. Our relationship is based on the analysis and modeling of detailed data from Monte Carlo simulations. As general properties that should hold for a wide class of adsorption scenarios, we find (i) that the particle-mediated adhesion energies of surfaces are maximal at intermediate bulk concentrations of the particles, and (ii) that the particle coverage in the bound state of the surfaces is twice the coverage in the unbound state at these bulk concentrations.DFG, GRK 1524, Self-Assembled Soft-Matter Nanostructures at Interface

Barriers for façade integration of solar technologies

Solar energy has been actively promoted as a clean energy source for a long time; however, solar technologies have not been widely used in the built environment, mostly limiting their operation to industrial and macroscale applications. Along with commercially available products such as building integrated PV panels (BIPV) or building integrated solar thermal collectors (BIST); novel solar cooling integrated facades are seen as interesting alternatives for the development of new active façade components for high-performing commercial buildings. Nevertheless, there are barriers to overcome to push for widespread application of architecturally integrated solar façades. This chapter identifies perceived barriers for widespread façade integration of solar technologies, to explore the current scenario and generate guidelines for future developments. To achieve this, the chapter discusses the results of the second part of the survey presented in the previous chapter, which addresses the perceived potential and specific issues for the integration of solar technologies. General results point to economic aspects as the main barrier to overcome, followed by particular issues related to current limitations of components and architectural products. In this aspect, most mentions point to performance, aesthetics and technical complexity of current systems as issues to improve in order to promote the development of solar integrated architectural products

Gains and Losses in Functionality – An Experimental Investigation of the Effect of Software Updates on Users’ Continuance Intentions

Although software updates are ubiquitous in professional and private IS usage, their impact on user behaviors has received little attention in post-adoption research. Based on expectation-confirmation-theory and the IS continuance model, we investigate the effects of gaining and loosing features through updates on expert and novice users’ continuance intentions (CI). In a vignette based experiment, we find that updates which add features to software after its release increase novices’ CI above and beyond a level generated by a monolithic software package that contains the entire feature set from the beginning. With diminished CI, experts show a contrary reaction to the same update. Losing features through an update, on the other hand, severely diminishes CI for experts and novices alike. Mediation analysis reveals positive disconfirmation of previous expectations as psychological mechanism behind novices’ counter-intuitive and somewhat non-rational responses to gaining features through an update. Implications for research and practice are derived

Solar cooling integrated facades

Solar cooling systems have gained increased attention these last years, for their potential to lower indoor temperatures using renewable energy. However, architectural integration of these systems in buildings has not been fully explored. Current developments such as small scale solar driven heat pumps and solar cooling kits commercially available for application raise questions about how to successfully integrate these systems into buildings, while present interesting opportunities for the development of new performance based façade components or even self-sustaining cooling façade modules for high-performing commercial buildings. So, what are the conceptual issues and state-of-the-art components and systems to consider for solar cooling façade integration? This chapter discusses current possibilities for façade integration of solar cooling systems, generating a framework for the understanding and further development of solar cooling façade systems. The proposed framework was made by means of a review of solar cooling technologies and solar cooling façade concepts reported by several researchers. The outcomes of the chapter are a matrix outlining the possibilities for the integration of several components and subsystems from the entire cooling process (cooling generation, distribution and delivery), and an early assessment of the development level of state-of-the-art experiences within the field considering examples from current research projects and working prototypes, for the development of solar cooling integrated façade concepts

Reinforcement learning for an intelligent and autonomous production control of complex job-shops under time constraints

Reinforcement learning (RL) offers promising opportunities to handle the ever-increasing complexity in managing modern production systems. We apply a Q-learning algorithm in combination with a process-based discrete-event simulation in order to train a self-learning, intelligent, and autonomous agent for the decision problem of order dispatching in a complex job shop with strict time constraints. For the first time, we combine RL in production control with strict time constraints. The simulation represents the characteristics of complex job shops typically found in semiconductor manufacturing. A real-world use case from a wafer fab is addressed with a developed and implemented framework. The performance of an RL approach and benchmark heuristics are compared. It is shown that RL can be successfully applied to manage order dispatching in a complex environment including time constraints. An RL-agent with a gain function rewarding the selection of the least critical order with respect to time-constraints beats heuristic rules strictly by picking the most critical lot first. Hence, this work demonstrates that a self-learning agent can successfully manage time constraints with the agent performing better than the traditional benchmark, a time-constraint heuristic combining due date deviations and a classical first-in-first-out approach

Production of the dinoflagellate Amphidoma languida in a large scale photobioreactor and structure elucidation of its main metabolite AZA-39

Shellfish contamination with azaspiracids (AZA) is a major and recurrent problem for the Irish shellfish industry. Amphidoma languida, a small thecate dinoflagellate of the family Amphidomataceae, is widely distributed in Irish coastal waters and is one of the identified source species of azaspiracids. Irish and North Sea strains of Am. languida have been found to produce as major metabolites AZA-38 and -39 whose structures have only been provisionally elucidated by mass spectrometry and their toxic potential is currently unknown. In order to provide pure AZA-38 and -39 for subsequent structural and toxicological analyses, we present the first successful large-scale culture of Am. languida. A 180 L in house prototype bioreactor was used for culture growth and harvesting in semi-continuous mode for two months. Two different runs of the photobiorector with different light and pH setting showed the highest toxin yield at higher light intensity and slightly higher pH. AZA-38 and -39 cell quota were measured throughout the complete growth cycle with AZA-39 cell quota increasing in proportion to AZA-38 at late stationary to senescence phase. Over two experiments a total of 700 L of culture was harvested yielding 0.45 mg of pure AZA-39. The structure of AZA-39 was elucidated through NMR data analyses, which led to a revision of the structure proposed previously by mass spectrometry. While the spirotetrahydrofuran/tetrahydrofuran of rings A and B has been confirmed by NMR for AZA-39, a methyl is still present in position C-14 and the carboxylic acid chain is different from the structure proposed initially

Ferritin encapsulation of artificial metalloenzymes: engineering a tertiary coordination sphere for an artificial transfer hydrogenase

Ferritin, a naturally occuring iron-storage protein, plays an important role in nanoengineering and biomedical applications. Upon iron removal, apoferritin was shown to allow the encapsulation of an artificial transfer hydrogenase (ATHase) based on the streptavidin-biotin technology. The third coordination sphere, provided by ferritin, significantly influences the catalytic activity of an ATHase for the reduction of cyclic imines

Rationale for prostaglandin I2 in bone marrow oedema – from theory to application

Introduction: Bone marrow oedema (BME) and avascular osteonecrosis (AVN) are disorders of unclear origin. Although there are numerous operative and non-operative treatments for AVN, pain management in patients with AVN remains challenging. Prostaglandins play an important role in inflammatory responses and cell differentiation. It is thought that prostaglandin I2 ([PGI2] or synonoma prostacyclin) and its analogues promote bone regeneration on a cellular or systemic level. The purpose of this study was to assess the curative and symptomatic efficacy of the prostacyclin analogue iloprost in BME and AVN patients. Method: We are reporting on 50 patients (117 bones) affected by BME/AVN who were treated with iloprost. Pain levels before, during and 3 and 6 months after iloprost application were evaluated by a visual analogue scale (VAS). The short form(SF)-36 health survey served to judge general health status before and after treatment. Harris Hip Score (HHS) and Knee Society Score (KSS) were performed as functional scores and MRI and X-rays before and 3 and 6 months after iloprost application served as objective parameters for morphological changes of the affected bones. Results: We found a significant improvement in pain, functional and radiological outcome in BME and early AVN stages after iloprost application, whereas patients with advanced AVN stages did not benefit from iloprost infusions. Mean pain level decreased from 5.26 (day 0) to 1.63 (6 months) and both HHS and KSS increased during follow-up. Moreover, the SF-36 increased from 353.2 (day 0) to 560.5 points (6 months). We found a significant decrease in BME on MRI scans after iloprost application. Conclusions: In addition to other drugs, iloprost may be an alternative substance which should be considered in the treatment of BME/AVN-associated pain

IL28B genetic variants and gender are associated with spontaneous clearance of hepatitis C virus infection

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90125/1/j.1365-2893.2011.01497.x.pd