Background:The oligomerization of GRASP65 and GRASP55 is required to tether Golgi membranes. Results: The crystal structures reveal two types of intermolecular interactions, and biochemical and cellular assays confirm these observations. Conclusion: Two relatively weak interactions in combination are needed for GRASP-mediated Golgi stacking. Significance: These data suggest a novel mode of Golgi membrane stacking by the GRASP proteins.
An environmentally benign and homogeneous basefree route for 5-hydroxymethyl-2-furfural (HMF) aerobic oxidation to 2,5-furandicarboxylic acid (FDCA) in water was reported using Mg−Al−CO 3 hydrotalcite-supported Pd nanoparticles (xPd/HT-n) as catalyst. The influences of the Mg/Al molar ratio of hydrotalcite and Pd loading amount on the catalytic performance of these catalysts were originally systematically investigated. These catalysts exhibited excellent catalytic activity and FDCA selectivity in the HMF oxidation, especially for 2%Pd/HT-5 and 2%Pd/HT-6; >99.9% FDCA yields were achieved for 8 h under ambient pressure and homogeneous base-free conditions. The remarkably improved catalytic performance could be attributed to the suitable basicity of the Mg−Al−CO 3 hydrotalcite and the abundant OH − groups on the surface of hydrotalcite. The plausible reaction mechanism was proposed based on the results of a series of controlled experiments. Furthermore, these catalysts were quite stable and could be reused at least five times without obvious loss in reaction activity.
Acyl-ACP thioesterase (TE) catalyzes the hydrolysis of thioester bonds during type II fatty acid synthesis and directly determines fatty acid chain length. Most TEs are responsible for recognition of 16:0 and 18:1 substrates, while specific TEs interrupt acyl-ACP elongation at C8-C14. However, the acyl selection mechanism of TE has not been thoroughly elucidated to date. In this study, the crystal structure of the C12-specific thioesterase FatB from Umbellularia californica, which consists of two independent hotdog domains, was determined. An uncanonical Asp-His-Glu catalytic network was identified on the C-terminal hotdog domain, whereas the substrate binding pocket was determined to be on the N-terminal hotdog domain. Moreover, we elucidated UcFatB's substrate selection mechanism, which is accommodated by several unconservative amino acids on the β5, β2, and β4 sheets and enclosed by T137 on the α1 helix. On this basis, the C12-specific TE was rationally redesigned toward C14 selectivity by tuning the substrate binding pocket capacity. The T137G mutant demonstrated comparative relative activity on C14 substrates compared to C12 substrates in vitro. Furthermore, the reconstructed UcFatB_T137G achieved C14 fatty acid content up to 40% in contrast to 10% C14 from the wild type in engineered E. coli cells. The unraveled substrate selection mechanism of TE provides a new strategy for tailoring fatty acid synthesis.
Two-dimensional carbon nanowalls (CNWs) were prepared by microwave plasma-enhanced chemical-vapor deposition and scanning electron microscopy was used to observe their morphologies. The Raman observations of different sample orientations and polarizations show that CNWs are well crystallized. Micro-Raman scattering measurements were also carried out with different excitation laser lines (325, 488, 514, 532, and 633 nm). The D band shows a very strong shift of 46.19 cm(-1)eV with excitation laser energy and this has been explained by the double resonance effect. The decreasing intensity ratios IDIG and ID'/IG with increasing laser excitation energy were detected and discussed.
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