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Examines crystal and molecular structures and hydrogen bonding system in cellulose II using neutron diffraction data. Mercerization of NaOH/H2O; Localization of the labile hydrogen atom involved in the bonding; Analysis of hydrogen bonds in cellulose II; Calculation of Fourier difference maps; Coordinates of all atoms in cellulose II.

Crystals of the blue copper protein amicyanin suitable for neutron diffraction were grown by the sitting-drop method, followed by repeated macroseeding using solutions prepared with D2O. Although the crystal sizes were the same, crystals grown using solutions made up in H2O in the initial stages of macroseeding and solutions with D2O in later stages did not diffract neutrons well. However, when the protein was initially exchanged with buffered D2O and then crystallized and also macroseeded using solutions made up in D2O throughout, the crystals diffracted neutrons to high resolution. One of those crystals was used to collect a data set to a resolution of 1.9 Å. [ABSTRACT FROM AUTHOR]

The joint x-ray/neutron diffraction model of the Type I copper protein, amicyanin from Paracoccus denitrificans was determined at 1.8 Å resolution. The protein was crystallized using reagents prepared in D2O. About 86% of the amide hydrogen atoms are either partially or fully exchanged, which correlates well with the atomic depth of the amide nitrogen atom and the secondary structure type, but with notable exceptions. Each of the four residues that provide copper ligands is partially deuterated. The model reveals the dynamic nature of the protein, especially around the copper-binding site. A detailed analysis of the presence of deuterated water molecules near the exchange sites indicates that amide hydrogen exchange is primarily due to the flexibility of the protein. Analysis of the electron transfer path through the protein shows that residues in that region are highly dynamic, as judged by hydrogen/deuterium exchange. This could increase the rate of electron transfer by transiently shortening through-space jumps in pathways or by increasing the atomic packing density. Analysis of C-H⋯X bonding reveals previously undefined roles of these relatively weak H bonds, which, when present in sufficient number can collectively influence the structure, redox, and electron transfer properties of amicyanin. [ABSTRACT FROM AUTHOR]

In this quantum chemical study, we explore hydrogen bonding (H-bonding) and stacking interactions in different crystalline cellulose allomorphs; namely, cellulose Iβ and cellulose IIII. We consider a model system representing a cellulose crystalline core made from six cellobiose units arranged in three layers with two chains per layer. We calculate the contributions of intrasheet and intersheet interactions to the structure and stability in both cellulose Iβ and cellulose IIII crystalline cores. Reference structures for this study were generated from molecular dynamics simulations of water-solvated cellulose Iβ andIIIβ fibrils. A systematic analysis of various conformations describing different mutual orientations of cellobiose units is performed using the hybrid density functional theory with the M06-2X with 6-31+ G(d,p) basis sets. We dissect the nature of the forces that stabilize the cellulose Iβ and cellulose IIII crystalline cores and quantify the relative strength of H-bonding and stacking interactions. Our calculations demonstrate that individual H-bonding interactions are stronger in cellulose Iβ than in cellulose IIII; however, the total H-bonding contribution to stabilization is larger in cellulose IIII because of the highly cooperative nature of the H-bonding network. In addition, we observe a significant contribution from cooperative stacking interactions to the stabilization of cellulose Iβ. The theory of atoms-in-molecules (AIM) has been employed to characterize and quantify these intermolecular interactions. AIM analyses highlight the role of nonconventional CH &#x22EF O H-bonding in the cellulose assemblies. Finally, we calculate molecular electrostatic potential maps for the cellulose allomorphs that capture the differences in chemical reactivity of the systems considered in our study. [ABSTRACT FROM AUTHOR]

The biosyntheses of oligosaccharides and glycoconjugates are conducted by glycosyltransferases. These extraordinarily diverse and widespread enzymes catalyze the formation of glycosidic bonds through the transfer of a monosaccharide from a donor molecule to an acceptor molecule, with the stereochemistry about the anomeric carbon being either inverted or retained. Human ABO(H) blood group A α-1,3- N-acetylgalactosaminyltransferase (GTA) generates the corresponding antigen by the transfer of N-acetylgalactosamine from UDP-GalNAc to the blood group H antigen. To understand better how specific active-site-residue protons and hydrogen-bonding patterns affect substrate recognition and catalysis, neutron diffraction studies were initiated at the Protein Crystallography Station (PCS) at Los Alamos Neutron Science Center (LANSCE). A large single crystal was subjected to H/D exchange prior to data collection and time-of-flight neutron diffraction data were collected to 2.5 Å resolution at the PCS to ∼85% overall completeness, with complementary X-ray diffraction data collected from a crystal from the same drop and extending to 1.85 Å resolution. Here, the first successful neutron data collection from a glycosyltransferase is reported. [ABSTRACT FROM AUTHOR]

The article reports on the use of the metalloenzyme carbonic anhydrase (CA) to form carbonic acid and hydrogen atom from the catalysis of hydrated carbon dioxide. The extra proton formed during the hydration is removed from the hydrogen network of CA. An isoform of CA is used to determine the conformation of the proton shuttle, pattern of hydrogen bonding and orientation of the water molecules used in the proton transfer.

Abstract: Long-pulse spallation sources will offer a very high time-integrated neutron flux similar to that of the best steady-state sources. Using Monte Carlo simulations we show that the exceptional source qualities translate directly into strongly enhanced instrument performance for a large class of instruments ranging from high-resolution backscattering to low-resolution small-angle scattering. The relation of the source duty cycle to the required wavelength resolution of the instrument is in this context a crucial performance indicator. Very large additional gains are achievable by properly tailoring the instrument parameters to the source characteristics and by fully exploiting modern neutron optics. In all cases investigated the long-pulse structure can be turned into an asset for the instrument design by using the known concepts of pulse shaping and frame multiplication. [Copyright &y& Elsevier]

Photoactive yellow protein (PYP) from Halorhodospira halophila is a soluble 14 kDa blue-light photoreceptor. It absorbs light via its para-coumaric acid chromophore (pCA), which is covalently attached to Cys69 and is believed to be involved in the negative phototactic response of the organism to blue light. The complete structure (including H atoms) of PYP has been determined in D2O-soaked crystals through the application of joint X-ray (1.1 Å) and neutron (2.5 Å) structure refinement in combination with cross-validated maximum-likelihood simulated annealing. The resulting XN structure reveals that the phenolate O atom of pCA accepts deuterons from Glu46 Oℇ2 and Tyr42 Oη in two unusually short hydrogen bonds. This arrangement is stabilized by the donation of a deuteron from Thr50 Oγ1 to Tyr42 Oη. However, the deuteron position between pCA and Tyr42 is only partially occupied. Thus, this atom may also interact with Thr50, possibly being disordered or fluctuating between the two bonds. [ABSTRACT FROM AUTHOR]