![]() Chemical shift anisotropy (CSA) can be measured for multiple sites in a site-specific manner using magic angle spinning (MAS) NMR spectroscopy, where a chemical shift recoupling sequence is introduced into multidimensional experiments. While solution NMR methods yield only the isotropic chemical shifts, in solid-state NMR (SSNMR) chemical shift tensors (CSTs) can be recorded. Among these, chemical shift perturbations are the easiest to measure directly using multidimensional homonuclear and heteronuclear correlation spectroscopy, as chemical shift parameters are highly sensitive to the local changes in the electronic environment due to HB interactions. In particular, solution NMR signatures include chemical shift changes of the nuclei participating in HB interactions, reduced amide proton exchange rates, and indirect scalar or J-couplings mediated across hydrogen bonds to identify residues involved in hydrogen bonds. NMR spectroscopy has long been used in the identification of hydrogen bonds in peptides and proteins through a number of NMR parameters. Hydrogen bond (HB) is one of the important noncovalent interactions stabilizing folded proteins. Our findings highlight the potential for the use of 15N CSTs in protein structure refinement. The downfield chemical shift change of backbone amide nitrogen nuclei with increasing hydrogen bond strength is manifested in the negative correlation of the principal components with hydrogen bond distance for both α-helical and β-sheet secondary structure elements. Our results show that the principal component δ 11 is very sensitive to the presence of hydrogen bonding interactions due to its unique orientation in the molecular frame. The 15N CSTs were measured by a symmetry-based CSA recoupling method, ROCSA. Here we present experimental results and statistical analysis of backbone amide 15N CSTs for 100 residues of four proteins, two E. 15N CST are very sensitive to hydrogen bonding, yet they have been reported for very few proteins to date. Those local structures are stabilised by hydrogen bonds and connected by tight turns and loose, flexible loops.Chemical shift tensors (CSTs) are an exquisite probe of local geometric and electronic structure. For example, the proteins in silk have a beta sheet structure. Two or more parallel or anti-parallel adjacent polypeptide chains of beta strand stabilised by hydrogen bonds form a beta sheet. A Beta strand (β-strand) is a stretch of polypeptide chain, typically 3 to 10 amino acids long, with its backbone in an almost fully extended conformation. The other common type of secondary structure is the beta strand. The alpha helix (α-helix) has a right-handed spiral conformation, in which every backbone N-H group donates a hydrogen bond to the backbone C=O group of the amino acid four residues before it in the sequence. There are two common types of secondary structure (Figure 11). ![]() Secondary structure refers to regular, local structure of the protein backbone, stabilised by intramolecular and sometimes intermolecular hydrogen bonding of amide groups. Protein structures are also classified by their secondary structure.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |