Magic angle spinning and static oriented sample NMR studies of the relaxation in the rotating frame of membrane peptides

Abstract

To demonstrate the influence of motions with medium-to-slow correlation times ͑milliseconds to nanoseconds͒, a systematic study of the spin-lattice relaxation in the rotating frame was conducted for several nuclei ͑ 1 H, 13 C, and 15 N͒ in small membrane polypeptides, either in oriented or magic angle spinning samples. This study not only assesses the validity of some motional models, but also characterizes the magnetization relaxation rates crucial for the design of polarization transfer experiments. It was found that relaxation time constant ͑T 1 ͒ values on the order of 10 −3 -10 −2 s for backbone nuclei and their dependence on sample orientation are consistent with the model of transmembrane polypeptides undergoing axial diffusion ͑ c ϳ 10 −8 -10 −7 s͒ and small amplitude off-axis reorientation ͑ c ϳ 10 −6 -10 −5 s͒.

Effects of amantadine on the dynamics of membrane-bound influenza A M2 transmembrane peptide studied by NMR relaxation

“…The faster diffusion rates result from the one to two orders of magnitude reduction of the prefactor τ 0 , as obtained from the high-temperature intercepts of the $\ln \left(T_{1\rho }^{-1}\right)$ curves. The intercept depends both on τ 0 and the dipolar second moment (equation 9), whose exact magnitude differs somewhat between different theories, depending on how many spin interactions are included and whether the MAS or the static condition is operative (Fares et al, 2005, Huster et al, 2001, Mehring et al, 1983). However, the ratio of the intercepts between the apo and bound peptide depends only on τ 0 .…”

“…Since the Larmor frequencies are three to four orders of magnitude larger than ω e ( ω H = 2π × 600 MHz, ω C = 2π × 150 MHz, and ω e = 2π × 61.2 kHz in our experiments), for motions in the tens to hundreds of kilohertz regime, one can safely ignore the spectral density terms at the Larmor frequencies. Taking into account magic-angle spinning at a frequency ω R , the powder averaged T 1ρ for the rotating-frame relevant part is (Fares et al, 2005): $$true\langle T_{1\rho }^{-1}true\rangle =\Delta M_2(S,{\delta }_{CH},{\delta }_{HH},\beta )\cdot [J(2{\omega }_e+2{\omega }_R)+J(2{\omega }_e-2{\omega }_R)+J(2{\omega }_e+{\omega }_R)+J(2{\omega }_e-{\omega }_R)]$$ Here Δ M 2 is the product of the dynamic portion of the dipolar second moment and orientational terms that transform spin interaction tensors from their molecule-fixed principal axis frames to the rotor frame (Fares et al, 2005). The dynamic portion of the dipolar second moment is approximately (1 – S 2 ) times the rigid-limit dipolar second moment, where the order parameter S represents the orientation-invariant part of the interaction.…”

Structure and Dynamics of the HIV-1 Vpu Transmembrane Domain Revealed by Solid-State NMR with Magic-Angle Spinning

“…Circular dichroism measurements on Vpu indicate that this peptide contains 55% R-helical structure in 2,2,2-trifluoroethanol/H 2 O (TFE/H 2 O) solutions (27). Similar measurements on a series of overlapping peptides from Vpu- (28)(29)(30)(31)(32)(33)(34)(35)(36)(37)(38)(39)(40)(41)(42) to Vpu (67)(68)(69)(70)(71)(72)(73)(74)(75)(76)(77)(78)(79)(80)(81) showed significant helical content for residues 42-50 and 57-69 (28). Fourier transform infrared (FTIR) dichroism spectroscopy of Vpu in DMPC bilayers suggests that this peptide is predominantly R-helical in nature (29).…”

Full-length Vpu and human CD4(372–433) in phospholipid bilayers as seen by magic angle spinning NMR

“…In contrast, 1 H-13 C polarization transfer by insensitive nuclei enhanced by polarization transfer (INEPT) (Morris and Freeman, 1979;Burum and Ernst, 1980) is effective only if dipolar couplings are averaged out by large amplitude motions on time scales of < 10 -5 s (Andronesi et al, 2005;Yang et al, 2011). Slower motions in the range between milliseconds and microseconds on the other hand can affect T 1ρ relaxation and thus decrease the CP efficiency even if the amplitude of the motion is not large enough for isotropic averaging of the dipolar coupling (Fares et al, 2005;Sharpe et al, 2006). CP-based 13 C MAS spectra of proteoliposomes containing either CD4(372-433) or Vpu show 13 C signals typical for proteins both above and below the lipid phase transition temperature (Figure 1).…”