Structural Basis for Activation of Human Sirtuin 6 by Fluvastatin.

Sirtuins are NAD+-dependent protein lysine deacylases that are considered attractive drug targets for aging-related diseases. Sirt6 deacetylates, e.g., transcription factors and histone H3, and regulates metabolic processes and stress responses. It has been implicated in lifespan extension and tumor suppression. Sirt6 deacetylase activity can be stimulated with small molecules, and fluvastatin, an FDA-approved synthetic statin, was recently described as a novel Sirt6 activator. We studied the molecular details of this effect on Sirt6 in deacylation assays and by solving a crystal structure of a Sirt6/fluvastatin complex. We find that fluvastatin inhibits Sirt1-3 at higher concentrations but has a unique, activating effect on Sirt6. The complex structure reveals that fluvastatin occupies the Sirt6 substrate acyl channel exit, similar to other, unrelated activator families, providing interaction details that will support the development of potent, druglike Sirt6 activators.

Structural basis for the activation and inhibition of Sirtuin 6 by quercetin and its derivatives.

Mammalian Sirtuin 6 (Sirt6) is an NAD+-dependent protein deacylase regulating metabolism and chromatin homeostasis. Sirt6 activation protects against metabolic and aging-related diseases, and Sirt6 inhibition is considered a cancer therapy. Available Sirt6 modulators show insufficient potency and specificity, and even partially contradictory Sirt6 effects were reported for the plant flavone quercetin. To understand Sirt6 modulation by quercetin-based compounds, we analysed their binding and activity effects on Sirt6 and other Sirtuin isoforms and solved crystal structures of compound complexes with Sirt6 and Sirt2. We find that quercetin activates Sirt6 via the isoform-specific binding site for pyrrolo[1,2-a]quinoxalines. Its inhibitory effect on other isoforms is based on an alternative binding site at the active site entrance. Based on these insights, we identified isoquercetin as a ligand that can discriminate both sites and thus activates Sirt6 with increased specificity. Furthermore, we find that quercetin derivatives that inhibit rather than activate Sirt6 exploit the same general Sirt6 binding site as the activators, identifying it as a versatile allosteric site for Sirt6 modulation. Our results thus provide a structural basis for Sirtuin effects of quercetin-related compounds and helpful insights for Sirt6-targeted drug development.

An Autonomous Fruit and Vegetable Harvester with a Low-Cost Gripper Using a 3D Sensor.

Reliable and robust systems to detect and harvest fruits and vegetables in unstructured environments are crucial for harvesting robots. In this paper, we propose an autonomous system that harvests most types of crops with peduncles. A geometric approach is first applied to obtain the cutting points of the peduncle based on the fruit bounding box, for which we have adapted the model of the state-of-the-art object detector named Mask Region-based Convolutional Neural Network (Mask R-CNN). We designed a novel gripper that simultaneously clamps and cuts the peduncles of crops without contacting the flesh. We have conducted experiments with a robotic manipulator to evaluate the effectiveness of the proposed harvesting system in being able to efficiently harvest most crops in real laboratory environments.

Structural Basis of Sirtuin 6 Inhibition by the Hydroxamate Trichostatin A: Implications for Protein Deacylase Drug Development.

Protein lysine deacylases comprise three zinc-dependent families and the NAD+-dependent sirtuins Sirt1-7, which contribute to aging-related diseases. Few Sirt6-specific inhibitors are available. Trichostatin A, which belongs to the potent, zinc-chelating hydroxamate inhibitors of zinc-dependent deacylases, was recently found to potently and isoform-specifically inhibit Sirt6. We solved a crystal structure of a Sirt6/ADP-ribose/trichostatin A complex, which reveals nicotinamide pocket and acyl channel as binding site and provides interaction details supporting the development of improved deacylase inhibitors.

Structural Basis of Sirtuin 6 Activation by Synthetic Small Molecules.

Sirtuins are protein deacylases regulating metabolism and stress responses, and are implicated in aging-related diseases. Small molecule activators for the human sirtuins Sirt1-7 are sought as chemical tools and potential therapeutics, such as for cancer. Activators are available for Sirt1 and exploit its unique N-terminus, whereas drug-like activators for Sirt2-7 are lacking. We synthesized and screened pyrrolo[1,2-a]quinoxaline derivatives, yielding the first synthetic Sirt6 activators. Biochemical assays show direct, substrate-independent compound binding to the Sirt6 catalytic core and potent activation of Sirt6-dependent deacetylation of peptide substrates and complete nucleosomes. Crystal structures of Sirt6/activator complexes reveal that the compounds bind to a Sirt6-specific acyl channel pocket and identify key interactions. Our results establish potent Sirt6 activation with small molecules and provide a structural basis for further development of Sirt6 activators as tools and therapeutics.

Synthesis and Adsorption Properties of Hierarchically Ordered Nanostructures Derived from Porous CaO Network.

Using the porous framework of CaO as templates and reagents, we explored a surfactant-free and economical method for preparing calcium silicate hydrate (CSH) hierarchically ordered nanostructures. Incorporation of SiO2 nanoparticles into the CaO framework, followed by a reaction assisted by hydrothermal treatment, resulted in the formation of CSH with well-defined morphologies. The structural features of CSH were characterized by 3-D hierarchical networks, wherein nanofibers assembled to form nanosheets, and nanosheets assembled to form hierarchically ordered structures. Investigation of the crystal growth mechanism indicated that the key to forming the CSH ordered assembly structure was confining the Ca/Si ratio within a small range. Nonclassic oriented aggregation mechanism was used to describe the crystal growth of nanosheets, while the porous CaO framework served as template/reagents responsible for the formation of hierarchical structures. The resulting CSH adsorbent exhibited better performance in removing Pb(II) compared with other types of random CSH adsorbents. Additionally, the hierarchical structure of CSH provided more pores and active sites as support for other active functional materials such as zerovalent iron (Fe0). As-produced CSH@Fe nanocomposite with self-supported structures displayed high capacities for removal of Pb(II) after five adsorption-desorption cycles, and high capacities for other heavy metal ions (Cu2+, Cd2+, and Cr2O72-) and organic contaminants.

Functionalized calcium silicate nanofibers with hierarchical structure derived from oyster shells and their application in heavy metal ions removal.

Inorganic hierarchical nanostructures have remarkable potential applications in environmental metal remediation; however, their applications usually suffer from low capacity, high cost, and difficulties in the recycling of adsorbents. We previously reported a facile strategy to synthesize acid-insoluble calcium silicate hydrates (CSH) from oyster shells, a representative kind of biowaste. However, little is known of the structure, size, and morphology of the as-prepared CSH, which hampers the improvement of their adsorption capacities. In this work, systematic investigation of the structures of as-generated CSH demonstrate that they have a hierarchically porous structure composed of thin nano-sheets, where each nano-sheet is assembled by nano-fibers with width of around ten nanometers. The hierarchical nanostructures with pore size of ∼12 nm provide a significant amount of active sites to graft polyethyleneimine (PEI), which enables the efficient extraction of both Cu(ii) cations and Cr(vi) anions from the aqueous solution. Batch experiments further indicate that the PEI-modified PCSH exhibit a maximum adsorption capacity of 203 and 256 mg g(-1) for Cu(ii) and Cr(vi), respectively, much higher than that of CSH, OS and many other adsorbents in literature. The adsorption of Cu(ii) and Cr(vi) proved to be spontaneous and exothermic. Combining the pH-dependent experiments with X-ray photoelectron spectroscopy analysis, the underlying mechanism is discussed. PCSH derived from OS biowaste maintains an efficient extraction ability toward Cu(ii) and Cr(vi) after five adsorption-desorption cycles. It is also applicable for treating various kinds of heavy metal ions and organic pollutants, showing potentially wide applications in water treatment.

Crystallization and preliminary X-ray diffraction analysis of the putative aldose 1-epimerase YeaD from Escherichia coli.

Escherichia coli YeaD (ecYeaD) is suggested to be a member of the galactose mutarotase-like superfamily. Galactose mutarotase is an enzyme that converts alpha-galactose to beta-galactose. The known structures of these galactose mutarotase-like proteins are similar to those of galactose mutarotases, with the catalytic residues being conserved, but there are some differences between them in the substrate-binding pocket. In order to reveal the specificity of ecYeaD, a three-dimensional structure is essential. Full-length ecYeaD with an additional 6xHis tag at the C-terminus was crystallized by the hanging-drop vapour-diffusion method using polyethylene glycol 4000 as a precipitant at 283 K. An X-ray diffraction data set was collected to a resolution of 1.9 A from a single flash-cooled crystal that belonged to space group P2(1)2(1)2(1).