Determination of 15N chemical shift tensor via 15N-2H dipolar coupling in Boc-glycylglycyl[15N glycine]benzyl ester

Density functional calculations of 15N chemical shifts in solvated dipeptides

“…A good agreement with the experimental data is also found for the angle β between the least shielded component (σ 11 ) of the 15 N shielding tensor and the NH bond. The values of β obtained here, from 13.5° to 19.8°, are well in the range of the experimental values (12°-24°) obtained by different NMR techniques, both solution and solid-state Oas et al 1987;Hiyama et al 1988;Shoji et al 1989;Mai et al 1993;Fushman et al 1998;Cornilescu and Bax 2000;Kurita et al 2003;Loth et al 2005;Hall and Fushman 2006;Vasos et al 2006). There seems to be a weak correlation between the β angle and secondary structure, with slightly smaller angles for the β-sheet than for the α-helix (mean β angles are 14.8° and 16.5°, respectively).…”

“…It is worth pointing out that in our data this difference arises primarily from σ 22 , which is systematically higher in α-helix (by 7.8 ppm on average), while the other two components of the 15 N shielding tensor (particularly σ 11 ) show a considerably smaller and less systematic difference between the β-sheet and α-helix conformations (see Tables 3, 4). The calculated 15 N CSA values also agree with the solid state NMR measurements in short peptides Oas et al 1987;Hiyama et al 1988;Shoji et al 1989;Mai et al 1993;Wu et al 1995). A good agreement with the experimental data is also found for the angle β between the least shielded component (σ 11 ) of the 15 N shielding tensor and the NH bond.…”

Variability of the 15N Chemical Shielding Tensors in the B3 Domain of Protein G from 15N Relaxation Measurements at Several Fields. Implications for Backbone Order Parameters

“…For each residue, the experimental values of the spectral density function J(ω) at ω=0, ω N , and 0.87ω H were directly derived from the relaxation data (R 1 , R 2 , NOE) at each field strength using the reduced spectral density approximation 48,49 , as follows: (15) (16) (17) Altogether this resulted in 15 values of J(ω) per residue, five of which were J(0) values derived from different-field measurements and which are expected to be the same within experimental precision. The LS parameters, (S 2 , τ loc ), and the 15 N CSA value for each residue were obtained from an unconstrained nonlinear minimization of the following target function: (18) where the sum is over all available ω i values for a given residue, and δJ i represents the experimental error in J(ω i ). This method is analogous to the "classical" LS analysis except that reduced spectral densities are being used and the CSA is an additional fitting parameter.…”

“…Amide 15 N CSTs in proteins present a particular challenge, because they are susceptible to a variety of factors, including conformations (torsion angles) of both current and preceding residues, hydrogen bonding, solvent accessibility, long range electrostatics, etc 11-14 . The complete chemical shielding tensor could, in principle, be measured directly by solid-state NMR methods, and such studies provided valuable information on 15 N CSTs in short peptides [15][16][17][18][19][20][21] . However, applications of these techniques to uniformly labeled proteins are still in development.…”

The counterreceptor binding site of human CD2 exhibits an extended surface patch with multiple conformations fluctuating with millisecond to microsecond motions

“…The three rates measured [the longitudinal relaxation rate, R,(N;), the transverse relaxation rate, RN(N,), and the heteronuclear cross relaxation rate, RHN(H: + N,)] relate directly to the relative distribution of the values of the spectral density functions as follows: whereA = Y ; N Y ;~~/~~;~N , B = A2wk/3, and E = 3A + B. For a CSA value of A = -160 ppm (Hiyama et al, 1988) and an internuclear I5N-'H bond distance of r N H = 1.02 8, (Keiter, 1986), the constantsA and B become -1.3 X lo9 (rad/s)2 and 0.9 X IO9 (radls)', respectively, at 500 MHz. Linear combinations of the three rates therefore provide a direct measure of J(w), without any assumptions about the shape of the spectral density function.…”