Dataset Information

Solid-state NMR and density functional theory studies of ionization states of thiamin.

ABSTRACT: Thiamin diphosphate (ThDP) is a key coenzyme in sugar metabolism. The 4'-aminopyrimidine ring of ThDP cycles through several ionization and tautomeric states during enzyme catalysis, but it is not fully understood which states are adopted during the individual steps of the catalytic cycle. Thiamin has been synthesized with labels selectively inserted into the C2 and C6' positions, as well as into the amino group, creating [C2, C6'-(13)C(2)] thiamin and [N4'-(15)N] thiamin. Magic-angle spinning (MAS) NMR spectroscopy has been employed to record the (13)C and (15)N chemical shift anisotropy (CSA) tensors for C2, C6', and N4' atoms. Our results indicate that the isotropic chemical shifts as well as the principal components of the (13)C and (15)N CSA tensors are very sensitive to the protonation states in these compounds and, therefore, permit differentiating between the two ionization states, 4-aminopyrimidine and 4-aminopyrimidinium. Using density functional theory (DFT), we have calculated the magnetic shielding anisotropy tensors of C2, C6', and N4' and found excellent agreement between the computed and the experimental tensors. Our findings indicate that MAS NMR spectroscopy in conjunction with DFT calculations is a sensitive probe of ionization states in the thiamin cofactor. The results of this study will serve as a guide for characterization of ionization and tautomeric states of thiamin in complexes with thiamin-dependent enzymes.

SUBMITTER: Paramasivam S

PROVIDER: S-EPMC3227141 | biostudies-literature | 2011 Feb

REPOSITORIES: biostudies-literature

ACCESS DATA

Publications

Solid-state NMR and density functional theory studies of ionization states of thiamin.

Paramasivam Sivakumar S Balakrishnan Anand A Dmitrenko Olga O Godert Amy A Begley Tadhg P TP Jordan Frank F Polenova Tatyana T

The journal of physical chemistry. B 20101222 4

Thiamin diphosphate (ThDP) is a key coenzyme in sugar metabolism. The 4'-aminopyrimidine ring of ThDP cycles through several ionization and tautomeric states during enzyme catalysis, but it is not fully understood which states are adopted during the individual steps of the catalytic cycle. Thiamin has been synthesized with labels selectively inserted into the C2 and C6' positions, as well as into the amino group, creating [C2, C6'-(13)C(2)] thiamin and [N4'-(15)N] thiamin. Magic-angle spinning ( ...[more]

PMID: 21175136

Similar Datasets

Project description:The native cellulose of bacterial, algal, and animal origins has been well studied structurally using X-ray and neutron diffraction and solid-state NMR spectroscopy, and is known to consist of varying proportions of two allomorphs, I? and I?, which differ in hydrogen bonding, chain packing, and local conformation. In comparison, cellulose structure in plant primary cell walls is much less understood because plant cellulose has lower crystallinity and extensive interactions with matrix polysaccharides. Here we have combined two-dimensional magic-angle-spinning (MAS) solid-state nuclear magnetic resonance (solid-state NMR) spectroscopy at high magnetic fields with density functional theory (DFT) calculations to obtain detailed information about the structural polymorphism and spatial distributions of plant primary-wall cellulose. 2D (13)C-(13)C correlation spectra of uniformly (13)C-labeled cell walls of several model plants resolved seven sets of cellulose chemical shifts. Among these, five sets (denoted a-e) belong to cellulose in the interior of the microfibril while two sets (f and g) can be assigned to surface cellulose. Importantly, most of the interior cellulose (13)C chemical shifts differ significantly from the (13)C chemical shifts of the I? and I? allomorphs, indicating that plant primary-wall cellulose has different conformations, packing, and hydrogen bonding from celluloses of other organisms. 2D (13)C-(13)C correlation experiments with long mixing times and with water polarization transfer revealed the spatial distributions and matrix-polysaccharide interactions of these cellulose structures. Celluloses f and g are well mixed chains on the microfibril surface, celluloses a and b are interior chains that are in molecular contact with the surface chains, while cellulose c resides in the core of the microfibril, outside spin diffusion contact with the surface. Interestingly, cellulose d, whose chemical shifts differ most significantly from those of bacterial, algal, and animal cellulose, interacts with hemicellulose, is poorly hydrated, and is targeted by the protein expansin during wall loosening. To obtain information about the C6 hydroxymethyl conformation of these plant celluloses, we carried out DFT calculations of (13)C chemical shifts, using the I? and I? crystal structures as templates and varying the C5-C6 torsion angle. Comparison with the experimental chemical shifts suggests that all interior cellulose favor the tg conformation, but cellulose d also has a similar propensity to adopt the gt conformation. These results indicate that cellulose in plant primary cell walls, due to their interactions with matrix polysaccharides, and has polymorphic structures that are not a simple superposition of the I? and I? allomorphs, thus distinguishing them from bacterial and animal celluloses.

Dataset Information

Solid-state NMR and density functional theory studies of ionization states of thiamin.

Publications

Solid-state NMR and density functional theory studies of ionization states of thiamin.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets