Code: WOB	Time Slot/Poster Number: 10:45-11:10	Session: NMR & Crytstallography
Stereochemistry Determination of Natural Products by NMR Residual Dipolar Couplings and Powder X-Ray Diffraction Analysis
Roberto R. Gil
Carnegie Mellon University, Pittsburgh, PA
Abstract
We will present a double-blind solution of the structure of a new withanolide from Jaborosa parviflora using NMR Residual Dipolar Couplings (RDCs) and Powder X-Ray Diffraction analysis (PXRD). In the present case, the use of conventional NMR experiments (NOE and 3J analysis) in combination with DFT calculations led to three possible solutions. However, both RDCs and PXRD independently gave the same unique conformation and configuration for the structure of the new isolate. By independently providing the same solution structure, these two relatively new methodologies cross-validate each other. We will also present the development of a new tunable, fast, cleaner and friendly NMR methodology to measure RDCs using reusable compressed PMMA gels. No special device needed.

Code: WOB	Time Slot/Poster Number: 11:10-11:25	Session: NMR & Crytstallography
NMR Crystallography in an Enzyme Active Site: Characterizing the Chemical Structure of Catalytic Intermediates in Tryptophan Synthase
Jinfeng Lai; Dimitri Niks; Yachong Wang; Michael F. Dunn; Leonard J Mueller
University of California, Riverside, Riverside, CA
Abstract
Chemical level details such as protonation and hybridization states are critical for understanding enzymatic mechanism. Even under high resolution, these are difficult to determine from X-ray crystallography. Here we make use of a combined SSNMR, X-ray crystallographic, and ab initio approach to determine chemically-rich crystal structures for enzymatic intermediates in tryptophan synthase. Substrate 13C and 15N chemical shifts are measured in the crystalline-state under conditions of active catalysis. Chemically-rich structural models are then developed using a synergistic approach in which the structure of the substrate is freely optimized in the presence of active-site sidechain residues. Various models of charge and protonation state for the substrate and nearby catalytic residues can be distinguished by their calculated effect on the chemical shifts.

Code: WOB	Time Slot/Poster Number: 11:25-11:50	Session: NMR & Crytstallography
Solution-State Crystallography or Just Plain Old NMR Spectroscopy?
Craig P Butts; Jeremy Harvey; Catharine Jones
University of Bristol, UK, Bristol, United Kingdom
Abstract
De novo quantitative molecular structure elucidation in solution is demonstrated using data derived only from NMR spectroscopy. A purely distance-geometry approach is used whereby internuclear distances are employed to generate both connectivity and conformational information simultaneously on the basis of NMR spectroscopic data. We demonstrate that rigid interproton distances can be determined with accuracies of <0.1 Angstroms in most cases, allowing discrimination between myriads of possible isomers without the need to pre-determine the bonding skeleton. The methodology is equally appropriate to flexible systems and over a range of molecular frameworks – limitations and applications will be discussed. Remarkably this technique works without relying on interpretation of traditional solution-state semi-qualitative information such as chemical shift or coupling constants, although these can aid connectivity determination in more complex cases. This solution-state technique complements the high precision and intermolecular information available from solid-state crystallography, with structure elucidation in a more convenient state of matter.

Code: WOB	Time Slot/Poster Number: 11:50-12:05	Session: NMR & Crytstallography
Refinement of high resolution structures in low resolution envelopes
Irene Amata1; Melanie Falb1; Frank Gabel4; Cameron Mackereth3; Tobias Madl2; Michael Sattler2; Teresa Carlomagno1; Bernd Simon1
1European Molecular Biology Laboratory (EMBL), Heidelberg, Germnay; 2Helmholtz Zentrum, München, Germany; 3Institut Européen de Chimie et Biologie, Pessac, France; 4Institut de Biologie Structurale, Grenoble, France
Abstract
We present a structure calculation protocol that uses a low resolution structure envelope and high resolution structural data for simultaneous refinement. Low resolution envelopes are determined from small angle x-ray or neutron scattering data (SAXS/SANS) or single particle electron microscopy (EM). The pre-calculated shapes are used in conjunction with NMR data such as NOE distance restraints, residual dipolar couplings (RDC) and paramagnetic relaxation enhancements (PRE) in simulated annealing protocols implemented in ARIA/CNS. The protocol can be used to calculate NMR structures de novo or to refine complexes with previously determined high-resolution structures from NMR or x-ray crystallography.

Code: WOB	Time Slot/Poster Number: 12:05-12:30	Session: NMR & Crytstallography
Determining Relative H-H Proximities from 1H Double-Quantum NMR Spectra of Organic Solids
Steven Brown
University of Warwick, Coventry, United Kingdom
Abstract
1H double-quantum (DQ) spectroscopy is being increasingly applied as a probe of proton-proton proximities. Enhanced resolution as compared to MAS alone can be achieved in a 1H DQ CRAMPS experiment. Based on applications to systems with known crystal structures, a rule of thumb has emerged whereby the observation of 1H DQ peaks is indicative of a H-H proximity within 3.5 Å. We have recently shown that quantitative information about H-H proximities can be obtained from the build-up of DQ peaks in 1H DQ CRAMPS spectra recorded with increasing numbers of POST-C7 recoupling elements. These build-up curves allow the reliable determination of relative H-H distances, even in dense networks of many dipolar-coupled spins, such as are present in organic molecules.