Halohydrin dehalogenases (HHDHs) are of biotechnological interest due to their promiscuous epoxide ring-opening activity with a set of negatively charged nucleophiles, enabling the formation of C−C, C−N, or C−O bonds. The recent discovery of HHDH-specific sequence motifs aided the identification of a large number of halohydrin dehalogenases from public sequence databases, enlarging the biocatalytic toolbox substantially. During the characterization of 17 representatives of these phylogenetically diverse enzymes, one HHDH, namely HheG from Ilumatobacter coccineus, was identified to convert cyclic epoxide substrates. The enzyme exhibits significant activity in the azidolysis of cyclohexene oxide and limonene oxide with turnover numbers of 7.8 and 44 s −1 , respectively. As observed for other HHDHs, the cyanide-mediated epoxide ring-opening proceeded with lower rates. Wild-type HheG displays modest enantioselectivity, as the resulting azido-and cyanoalcohols of cyclohexene oxide ring-opening were obtained in 40% enantiomeric excess. These biocatalytic findings were further complemented by the crystal structure of the enzyme refined to 2.3 Å. Analysis of HheG's structure revealed a large open cleft harboring the active site. This is in sharp contrast to other known HHDH structures and aids in explaining the special substrate scope of HheG.

Phenazines are bacterial virulence and survival factors with important roles in infectious disease. PhzF catalyzes a key reaction in their biosynthesis by isomerizing (2 S,3 S)-2,3-dihydro-3-hydroxy anthranilate (DHHA) in two steps, a [1,5]-hydrogen shift followed by tautomerization to an aminoketone. While the [1,5]-hydrogen shift requires the conserved glutamate E45, suggesting acid/base catalysis, it also shows hallmarks of a sigmatropic rearrangement, namely the suprafacial migration of a non-acidic proton. To discriminate these mechanistic alternatives, we employed enzyme kinetic measurements and computational methods. Quantum mechanics/molecular mechanics (QM/MM) calculations revealed that the activation barrier of a proton shuttle mechanism involving E45 is significantly lower than that of a sigmatropic [1,5]-hydrogen shift. QM/MM also predicted a large kinetic isotope effect, which was indeed observed with deuterated substrate. For the tautomerization, QM/MM calculations suggested involvement of E45 and an active site water molecule, explaining the observed stereochemistry. Because these findings imply that PhzF can act only on a limited substrate spectrum, we also investigated the turnover of DHHA derivatives, of which only O-methyl and O-ethyl DHHA were converted. Together, these data reveal how PhzF orchestrates a water-free with a water-dependent step. Its unique mechanism, specificity and essential role in phenazine biosynthesis may offer opportunities for inhibitor development.

Purpose This study aims to deal with actor engagement practices and identifies different roles in actor engagement (AE), using the service-dominant logic (S-D logic) literature and the pivotal concept of value co-creation within the frame of engagement platforms. Design/methodology/approach The context of this research is an online health community, provided by a pharmaceutical firm, which moderates the interaction between its members. The authors use a grounded theory approach with the methodology of netnography. These research are based on the approaches of ethnography and is a suitable qualitative method for analyzing human behavior in certain situations. Findings The results indicate that customers and/or actors operate as resource integrators in the perspective of S-D logic. Independent social and economic actors adopt both the roles of service providers and service beneficiaries in a reciprocal manner. Value co-creation in online communities based on practices, which actually define the respective role. Three main engagement practices are identified: information-, advising- and empathy-practices. Research limitations/implications The findings point to the importance of the dynamic and interactive concept of actor engagement and present a clearer understanding of customer, who act both in provider- and beneficiary-roles. However, it becomes evident that a customer orientation should address the actor playing a beneficiary-role, who uses (or selects) the value proposition, and not actors who play the role of financial resources provider. Originality/value In recent years, the construct of AE, and, in particular, customer engagement have been established both in theory and in practice. However, there are few empirical research publications so far, that try to explain engagement practices in online communities, especially in the healthcare sector.

We report the design, synthesis and biological evaluation of simplified analogues of the herbicidal natural product (+)‐cornexistin. Guided by an X‐Ray co‐crystal structure of cornexistin bound to transketolase from Zea mays, we attempted to identify the key interactions that are necessary for cornexistin to maintain its herbicidal profile. This resulted in the preparation of three novel analogues investigating the importance of substituents that are located on the nine‐membered ring of cornexistin. One analogue maintained a good level of biological activity and could provide researchers insights in how to further optimize the structure of cornexistin for commercialization in the future.

Phenazine sind farbige Verbindungen synthetischen und natürlichen Ursprungs. Sie standen am Anfang der synthetischen Farbenindustrie und führten zu wichtigen Entdeckungen in der Mikrobiologie. Ihre strukturelle Symmetrie spiegelt sich in ihrer Biosynthese wider.