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In this study we describe the crystal structures of the apoform, the binary and the ternary complexes of a double bond reductase from Malus domestica L. (MdDBR) and explore a range of potential substrates. The overall fold of MdDBR is similar to that of the medium chain reductase/dehydrogenase/zinc-dependent alcohol dehydrogenase-like family. Structural comparison of MdDBR with Arabidopsis thaliana DBR (AtDBR), Nicotiana tabacum DBR (NtDBR) and Rubus idaeus DBR (RiDBR) allowed the identification of key amino acids involved in cofactor and ligands binding and shed light on how these residues may guide the orientation of the substrates. The enzyme kinetic for the substrate trans-4-phenylbuten-2-one has been analyzed, and MdDBR activity towards a variety of substrates was tested. This enzyme has been reported to be involved in the phenylpropanoid pathway where it would catalyze the NADPH-dependent reduction of the α, β-unsaturated double bond of carbonyl metabolites. Our study provides new data towards the identification of MdDBR natural substrate and the biosynthetic pathway where it belongs. Furthermore, the originally proposed involvement in dihydrochalcone biosynthesis in apple must be questioned. [ABSTRACT FROM AUTHOR]

Abstract Erwinia tasmaniensis is an epiphytic bacterium related to the plant pathogen Erwinia amylovora , the etiological agent of fire blight. In this study the levansucrase from E. tasmaniensis (EtLsc) has been compared with the homologous enzyme from E. amylovora (EaLsc). We characterized the enzymatic activity and compared the products profile of both enzymes by High Performance Anion Exchange Chromatography coupled with Pulsed Amperometric Detector (HPAEC-PAD). Moreover we determined the crystal structure of EtLsc to understand the structural peculiarity causing the different product profiles of the two homologues. EtLsc exhibits increased efficiency in the production of FOS, resulting in a better catalyst for biotechnological synthesis than EaLsc. Based on our results, we propose that the role of this enzyme in the life cycle of the two bacteria is most likely related to survival, rather than linked to pathogenicity in E. amylovora. [ABSTRACT FROM AUTHOR]

Abstract A combination of tacrine and tryptophan led to the development of a new family of heterodimers as multi-target agents with potential to treat Alzheimer's disease. Based on the in vitro biological profile, compound S -K1035 was found to be the most potent inhibitor of human acetylcholinesterase (h AChE) and human butyrylcholinesterase (h BChE), demonstrating balanced IC 50 values of 6.3 and 9.1 nM, respectively. For all the tacrine-tryptophan heterodimers, favorable inhibitory effect on h AChE as well as on h BChE was coined to the optimal spacer length ranging from five to eight carbon atoms between these two pharmacophores. S -K1035 also showed good ability to inhibit A β 42 self-aggregation (58.6 ± 5.1% at 50 μM) as well as h AChE-induced A β 40 aggregation (48.3 ± 6.3% at 100 μM). The X-ray crystallographic analysis of Tc AChE in complex with S -K1035 pinpointed the utility of the hybridization strategy applied and the structures determined with the two K1035 enantiomers in complex with h BChE could explain the higher inhibition potency of S -K1035. Other in vitro evaluations predicted the ability of S -K1035 to cross blood-brain barrier and to exert a moderate inhibition potency against neuronal nitric oxide synthase. Based on the initial promising biochemical data and a safer in vivo toxicity compared to tacrine, S -K1035 was administered to scopolamine-treated rats being able to dose-dependently revert amnesia. Graphical abstract Image 1 Highlights • Tacrine-tryptophan hybrids inhibited both cholinesterases in nanomolar concentrations. • Highlighted compound S -K1035 displayed A β 42 self-aggregation as well as h AChE-induced A β 40 aggregation. • Complex of Tc AChE and S -K1035 was elucidated by X-ray crystallography. • Difference in activity between K1035 enantiomers was explored by conducting X-ray crystallography with h BChE. • In vivo pro-cognitive effect of S -K1035 was confirmed in scopolamine-induced amnesia model in rats. [ABSTRACT FROM AUTHOR]