Solid-state NMR of unlabeled plant cell walls: high-resolution structural analysis without isotopic enrichment

Background Multidimensional solid-state nuclear magnetic resonance (ssNMR) spectroscopy has emerged as an indispensable technique for resolving polymer structure and intermolecular packing in primary and secondary plant cell walls. Isotope (13C) enrichment provides feasible sensitivity for measuring 2D/3D correlation spectra, but this time-consuming procedure and its associated expenses have restricted the application of ssNMR in lignocellulose analysis. Results Here, we present a method that relies on the sensitivity-enhancing technique Dynamic Nuclear Polarization (DNP) to eliminate the need for 13C-labeling. With a 26-fold sensitivity enhancement, a series of 2D 13C–13C correlation spectra were successfully collected using the unlabeled stems of wild-type Oryza sativa (rice). The atomic resolution allows us to observe a large number of intramolecular cross peaks for fully revealing the polymorphic structure of cellulose and xylan. NMR relaxation and dipolar order parameters further suggest a sophisticated change of molecular motions in a ctl1 ctl2 double mutant: both cellulose and xylan have become more dynamic on the nanosecond and microsecond timescale, but the motional amplitudes are uniformly small for both polysaccharides. Conclusions By skipping isotopic labeling, the DNP strategy demonstrated here is universally extendable to all lignocellulose materials. This time-efficient method has landed the technical foundation for understanding polysaccharide structure and cell wall assembly in a large variety of plant tissues and species.

Controllable formation of unusual homocrystals in poly(L-lactic acid)/poly(D-lactic acid) asymmetric blends induced by the constraining effects of pre-existing stereocomplexes

Crystallization in confined environments usually induces polymers showing complicated crystallization kinetics and unusual crystalline structure. Beyond the typical confined polymer systems, pre-existing crystals can also exert confinement effects on the subsequent crystallization of polymorphic or multi-component polymers; this, however, is not well understood at present. Herein, poly(L-lactic acid)/poly(D-lactic acid) (PLLA/PDLA, abbreviated as L/D) asymmetric blends with various PDLA fractions (f D = 0.02–0.5) are chosen as a model system and the effects of pre-existing stereocomplexes (SCs) on the crystallization kinetics and polymorphic structure are investigated. It is found that unusual β-form homocrystals (HCs) of poly(lactic acid) can be formed in an asymmetric L/D blend, which are strongly influenced by the molecular weights (MWs) of the used polymers, L/D mixing ratio, thermal treatment temperature (T max) and crystallization temperature (T c). The formation of β-HCs is preferred in asymmetric L/D blends with low and medium MWs, medium f D (0.1–0.2), medium T max (170–200°C), and low T c (70–110°C). The metastable β-HCs reorganize into the more stable α-HCs via melt recrystallization in the heating process. It is proposed that the β-HC formation stems from the constraining effects of pre-existing SCs; this constraining effect is governed by the content of pre-existing unmelted SCs in the thermally treated samples.

Polymorphism of 3-(5-phenyl-1,3,4-oxadiazol-2-yl)- and 3-[5-(pyridin-4-yl)-1,3,4-oxadiazol-2-yl]-2H-chromen-2-ones

This study of 3-(5-phenyl-1,3,4-oxadiazol-2-yl)-2H-chromen-2-one, C17H10N2O3, 1, and 3-[5-(pyridin-4-yl)-1,3,4-oxadiazol-2-yl]-2H-chromen-2-one, C16H9N3O3, 2, was performed on the assumption of the potential anticancer activity of the compounds. Three polymorphic structures for 1 and two polymorphic structures for 2 have been studied thoroughly. The strongest intermolecular interaction is stacking of the `head-to-head' type in all the studied crystals. The polymorphic structures of 1 differ with respect to the intermolecular interactions between stacked columns. Two of the polymorphs have a columnar or double columnar type of crystal organization, while the third polymorphic structure can be classified as columnar-layered. The difference between the two structures of 2 is less pronounced. Both crystals can be considered as having very similar arrangements of neighbouring columns. The formation of polymorphic modifications is caused by a subtle balance of very weak intermolecular interactions and packing differences can be identified only using an analysis based on a study of the pairwise interaction energies.

Intrinsic Disorder of the BAF Complex: Roles in Chromatin Remodeling and Disease Development

The two-meter-long DNA is compressed into chromatin in the nucleus of every cell, which serves as a significant barrier to transcription. Therefore, for processes such as replication and transcription to occur, the highly compacted chromatin must be relaxed, and the processes required for chromatin reorganization for the aim of replication or transcription are controlled by ATP-dependent nucleosome remodelers. One of the most highly studied remodelers of this kind is the BRG1- or BRM-associated factor complex (BAF complex, also known as SWItch/sucrose non-fermentable (SWI/SNF) complex), which is crucial for the regulation of gene expression and differentiation in eukaryotes. Chromatin remodeling complex BAF is characterized by a highly polymorphic structure, containing from four to 17 subunits encoded by 29 genes. The aim of this paper is to provide an overview of the role of BAF complex in chromatin remodeling and also to use literature mining and a set of computational and bioinformatics tools to analyze structural properties, intrinsic disorder predisposition, and functionalities of its subunits, along with the description of the relations of different BAF complex subunits to the pathogenesis of various human diseases.