Metal-organic coordination networks (MOCNs) formed by coordination bonding between metallic centers and organic ligands can be efficiently engineered to exhibit specific magnetic, electronic, or catalytic properties [1]. Instead of depositing prefabricated MOCNs onto surfaces, it has been recently shown that two-dimensional (2D) MOCNs can be directly grown at metal surfaces under ultrahigh vacuum (UHV), thus creating highly regular 2D networks of metal atoms [2]. We show here [3] that this approach allows to predefine the geometry of the MOCN by using the substrate as a template to direct the formation of novel 1D metal-organic coordination chains (MOCCs).The templating role of substrates is well known in the field of surface epitaxial growth. Among the highly anisotropic substrates, the Cu(110) surface is one of the most commonly used. To demonstrate its strong 1D templating effect on organic molecules, a ligand with a triangular symmetry was selected, namely 1,3,5-benzenetri-carboxylic acid (trimesic acid, TMA). The three-fold rotation symmetry of TMA supports the formation of hexagonal 2D and 3D architectures, therefore strongly disfavoring the linear geometry.The deposition of TMA on Cu(110) under UHV at 300 K results in the formation of 1D chains along the <1bar10> direction, as observed by scanning tunneling microscopy (STM). This deposition temperature is high enough to provide mobile Cu adatoms through evaporation from kinks and steps onto the terraces. Analysis of similar systems by X-ray photoelectron spectroscopy showed that these adatoms catalyze the deprotonation of molecular carboxylate groups and are necessary for the formation of copper carboxylate complexes. The chains formed at 300 K typically show irregular kinks and poor long-range order. These inhomogeneities are removed by postannealing to 380-410 K to yield straight and highly periodic chains, referred to as MOCC-I hereafter.

Serratia marcescens and several other bacteria produce the red-colored pigment prodigiosin which possesses bioactivities as an antimicrobial, anticancer, and immunosuppressive agent. Therefore, there is a great interest to produce this natural compound. Efforts aiming at its biotechnological production have so far largely focused on the original producer and opportunistic human pathogen S. marcescens. Here, we demonstrate efficient prodigiosin production in the heterologous host Pseudomonas putida. Random chromosomal integration of the 21 kb prodigiosin biosynthesis gene cluster of S. marcescens in P. putida KT2440 was employed to construct constitutive prodigiosin production strains. Standard cultivation parameters were optimized such that titers of 94 mg/L culture were obtained upon growth of P. putida at 20°C using rich medium under high aeration conditions. Subsequently, a novel, fast and effective protocol for prodigiosin extraction and purification was established enabling the straightforward isolation of prodigiosin from P. putida growth medium. In summary, we describe here a highly efficient method for the heterologous biosynthetic production of prodigiosin which may serve as a basis to produce large amounts of this bioactive natural compound and may provide a platform for further in-depth studies of prodiginine biosynthesis.

The adsorption of trimesic acid (TMA) on Cu(110) has been studied in the temperature range between 130 and 550 K and for coverages up to one monolayer. We combine scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), reflection absorption infrared spectroscopy (RAIRS), X-ray photoemission spectroscopy (XPS), and density functional theory (DFT) calculations to produce a detailed adsorption phase diagram for the TMA/Cu(110) system as a function of the molecular coverage and the substrate temperature. We identify a quite complex set of adsorption phases, which are determined by the interplay between the extent of deprotonation, the intermolecular bonding, and the overall energy minimization. For temperatures up to 280 K, TMA molecules are only partly deprotonated and form hydrogen-bonded structures, which locally exhibit organizational chirality. Above this threshold, the molecules deprotonate completely and form supramolecular metal-organic structures with Cu substrate adatoms. These structures exist in the form of single and double coordination chains, with the molecular coverage driving distinct phase transitions.

Understanding the deactivation mechanism of 2-deoxy-d-ribose-5-phosphate aldolase by its natural substrate leads to a single mutant showing complete acetaldehyde resistance.

The deeply red-colored natural compound prodigiosin is a representative of the prodiginine alkaloid family, which possesses bioactivities as antimicrobial, antitumor, and antimalarial agents. Various bacteria including the opportunistic human pathogen Serratia marcescens and different members of the Streptomycetaceae and Pseudoalteromonadaceae produce prodiginines. In addition, these microbes generally accumulate many structurally related alkaloids making efficient prodiginine synthesis and purification difficult and expensive. Furthermore, it is known that structurally different natural prodiginine variants display differential bioactivities. In the herein described mutasynthesis approach, 13 different derivatives of prodigiosin were obtained utilizing the GRAS (generally recognized as safe) classified strain Pseudomonas putida KT2440. Genetic engineering of the prodigiosin pathway together with incorporation of synthetic intermediates thus resulted in the formation of a so far unprecedented structural diversity of new prodiginine derivatives in P. putida. Furthermore, the formed products allow reliable conclusions regarding the substrate specificity of PigC, the final condensing enzyme in the prodigiosin biosynthesis pathway of S. marcescens. The biological activity of prodigiosin toward modulation of autophagy was preserved in prodiginine derivatives. One prodiginine derivative displayed more potent autophagy inhibitory activity than the parent compound or the synthetic clinical candidate obatoclax.

The fabrication of novel 2D 1a,b and 3D 1c molecular nanoarchitectures is attracting increasing attention in various research fields ranging from materials science to nanotechnology. Among biomolecules, peptides are very favorable building blocks, owing to the ease of their synthesis, relative stability, and chemical and biological functionalization. 2 They have been used for the design and construction of nanostructures for diverse applications, such as templates for the growth of functional networks, 3 biosensors for monitoring enzymatic reactions, 4 and organic catalysts for asymmetric aldol reactions. 5 A large amount of ordered peptide nanostructures with different geometries, 6 including nanotubes, nanospheres and nanofilaments, have been produced in solution or in vacuum. Peptide monolayer structures self-assembled on solid surfaces typically show a strong tendency to form chains. 6c-e Two-dimensional (2D) extended arrangements are difficult to produce due to a pronounced anisotropy in the intermolecular interactions.Here we report on the ordering and interconnection of 1D dipeptide nanostructures. Individual diphenylalanine molecules (Phe-Phe, Figure 1), only form short isolated chains with a broad length distribution when deposited on Cu substrates. By exploiting 2D cocrystallization with the organic linker terephthalic acid (TPA), we show that continuous and highly periodic dipeptide arrangements can be formed on both the anisotropic Cu(110) and the isotropic Cu(100) surface. This approach might be extended to the fabrication of similar peptide-based nanostructures with potential applications in biocompatible functional surfaces.Scanning tunneling microscopy (STM) measurements of L-Phe-L-Phe molecules deposited under ultrahigh vacuum on Cu surfaces reveal a preferential self-organization in the form of 1D chains. On the Cu(110) surface the Phe-Phe chains are typically isolated and characterized by a high density of kinks. On Cu(100) the chains show four possible orientations and are typically shorter, and their distribution is similarly dispersed (see Figure S1 in the Supporting Information).The formation of isolated chains suggests different intra-and interchain interactions. The binding between Phe-Phe molecules, which results in the development of supramolecular chains, is most probably due to an interaction between the carboxylic group of one molecule and the amino group of the neighboring one. 7 On the other hand, a nonperfect matching of the chain structures with the underlying substrate might cause the frequent kink defects. The same mismatch could also generate a substrate-mediated repulsion among the chains and, similarly to what is observed in other systems, 8 result in their separation. Chain-chain repulsion and kink defects are the reasons why extended and ordered structures are never formed, independently of the molecular coverage (see Figure S1).In order to overcome this limitation, we have co-deposited a molecular linker (TPA) with the aim of connecting the isolated Phe-Phe chains by ef...

A one-pot consecutive two-enzyme sequential cascade toward chiral γ-butyrolactones using an enoate reductase as well as alcohol dehydrogenases in combination with a glucose dehydrogenase is reported. In this scalable process, the products were obtained in high yield (up to 90%) and with perfect enantioselectivity (98→99% ee). The starting materials, ethyl 4-oxo-pent-2enoates, are readily accessible via Wittig-type reactions. Furthermore, the stereoselectivity of the enoate reductase catalyzed reaction has been studied in detail, leading to deeper insights into the mechanism of this enzyme.

Understanding enzyme stability and activity in extremophilic organisms is of great biotechnological interest, but many questions are still unsolved. Using 2-deoxy-D-ribose-5-phosphate aldolase (DERA) as model enzyme, we have evaluated structural and functional characteristics of different orthologs from psychrophilic, mesophilic and hyperthermophilic organisms. We present the first crystal structures of psychrophilic DERAs, revealing a dimeric organization resembling their mesophilic but not their thermophilic counterparts. Conversion into monomeric proteins showed that the native dimer interface contributes to stability only in the hyperthermophilic enzymes. Nevertheless, introduction of a disulfide bridge in the interface of a psychrophilic DERA did confer increased thermostability, suggesting a strategy for rational design of more durable enzyme variants. Constraint network analysis revealed particularly sparse interactions between the substrate pocket and its surrounding α-helices in psychrophilic DERAs, which indicates that a more flexible active center underlies their high turnover numbers.