Random coil carbon chemical shifts of deoxyribonucleic acids

NMR proton chemical shift prediction of C·C mismatches in B-DNA

Accurate prediction of DNA chemical shifts facilitates resonance assignment and allows recognition of different conformational features. Based on the nearest neighbor model and base pair replacement approach, we have determined a set of triplet chemical shift values and correction factors for predicting the proton chemical shifts of B-DNA containing an internal C·C mismatch. Our results provide a reliable chemical shift prediction with an accuracy of 0.07 ppm for non-labile protons and 0.09 ppm for labile protons. In addition, we have also shown that the correction factors for C·C mismatches can be used interchangeably with those for T·T mismatches. As a result, we have generalized a set of correction factors for predicting the flanking residue chemical shifts of pyrimidine·pyrimidine mismatches.

Complete chemical shift assignment of the ssDNA in the filamentous bacteriophage fd reports on its conformation and on its interface with the capsid shell

The fd bacteriophage is a filamentous virus consisting of a circular single-stranded DNA (ssDNA) wrapped by thousands of copies of a major coat protein subunit (the capsid). The coat protein subunits are mostly α-helical and curved, and are arranged in the capsid in consecutive pentamers related by a translation along the main viral axis and a rotation of ~36° (C5S2 symmetry). The DNA is right-handed and helical, but information on its structure and on its interface with the capsid is incomplete. We present here an approach for assigning the DNA nucleotides and studying its interactions with the capsid by magic-angle spinning solid-state NMR. Capsid contacts with the ssDNA are obtained using a two-dimensional (13)C-(13)C correlation experiment and a proton-mediated (31)P-(13)C polarization transfer experiment, both acquired on an aromatic-unlabeled phage sample. Our results allow us to map the residues that face the interior of the capsid and to show that the ssDNA-capsid interactions are sustained mainly by electrostatic interactions between the positively charged lysine side chains and the phosphate backbone. The use of natural abundance aromatic amino acids in the growth media facilitated the complete assignment of the four nucleotides and the observation of internucleotide contacts. Using chemical shift analysis, our study shows that structural features of the deoxyribose carbons reporting on the sugar pucker are strikingly similar to those observed recently for the Pf1 phage. However, the ssDNA-protein interface is different, and chemical shift markers of base pairing are different. This experimental approach can be utilized in other filamentous and icosahedral bacteriophages, and also in other biomolecular complexes involving structurally and functionally important DNA-protein interactions.

NMR proton chemical shift prediction of T·T mismatches in B-DNA duplexes

A proton chemical shift prediction scheme for B-DNA duplexes containing a T·T mismatch has been established. The scheme employs a set of T·T mismatch triplet chemical shift values, 5'- and 3'-correction factors extracted from reference sequences, and also the B-DNA chemical shift values predicted by Altona et al. The prediction scheme was tested by eight B-DNA duplexes containing T·T mismatches. Based on 560 sets of predicted and experimental proton chemical shift values, the overall prediction accuracy for non-labile protons was determined to be 0.07 ppm with an excellent correlation coefficient of 0.9996. In addition, the prediction accuracy for 96 sets of labile protons was found to be 0.22 ppm with a correlation coefficient of 0.9961. The prediction scheme developed herein can facilitate resonance assignments of B-DNA duplexes containing T·T mismatches and be generalized for the chemical shift prediction of other DNA mismatches. Our chemical shift data will also be useful for establishing structure-chemical shift information in B-DNA containing mismatches.

Proton chemical shift prediction of A.A mismatches in B-DNA duplexes

A proton chemical shift prediction method has been developed for double helical DNAs containing A.A mismatches. This method makes use of the chemical shift prediction scheme for normal B-DNA duplexes developed by Altona and co-workers and a set of A.A mismatch triplet chemical shift values and corrections factors extracted from reference sequences. The triplet values are used for predicting chemical shifts of A.A mismatches whereas the normal B-DNA chemical shifts and correction factors are used for the flanking residues of A.A mismatches. Both 5'- and 3'-correction factors have been determined from the chemical shift differences upon replacing the A.A mismatch in a duplex with an A.T base pair. Based on 560 sets of predicted and experimental chemical shifts, the overall prediction accuracy for various types of protons has been determined to be 0.07 ppm with an excellent correlation coefficient of 0.9996.

DSHIFT: a web server for predicting DNA chemical shifts

DSHIFT is a web server for predicting chemical shifts of DNA sequences in random coil form or double helical B-form. The prediction methods are based on sets of published reference chemical shift values and correction factors which account for shielding or deshielding effects from neighboring nucleotides. Proton, carbon and phosphorus chemical shift predictions are available for random coil DNAs. For double helical B-DNA, only proton chemical shift prediction is available. Results from these predictions will be useful for facilitating NMR resonance assignments and investigating structural features of solution DNA molecules. The URL of this server is: http://www.chem.cuhk.edu.hk/DSHIFT.

Random coil phosphorus chemical shift of deoxyribonucleic acids

Random coil phosphorus chemical shift has been studied using 16 17-nucleotide DNA sequences. Due to the presence of residual base stacking in these sequences, the temperature and sequence effects were investigated at 50 and 55 degrees C. The phosphorus chemical shifts of random coil DNA sequences have been found to be independent of temperature. Sequence effect analysis shows that the phosphorus chemical shift of a nucleotide in a random coil DNA sequence depends on both its 5'- and 3'-nearest neighbors. A trimer model has been used to establish the random coil 31P chemical shift prediction protocol which shows an accuracy of 0.02 ppm.