Detection of correlated conformational fluctuations in intrinsically disordered proteins through paramagnetic relaxation interference.

Functionally relevant conformational states of intrinsically disordered proteins (IDPs) are typically concealed in a vast space of fast interconverting structures. Here we present a novel methodology, NMR-based paramagnetic relaxation interference (PRI), that allows for direct observation of concerted motions and cooperatively folded sub-states in IDPs. The proposed NMR technique is based on the exploitation of cross correlated electron-nuclear dipolar relaxation interferences in doubly spin-labeled proteins and probes the transient spatial encounter of electron-nucleus spin pairs.

Multiplet component separation for measurement of methyl 13C-1H dipolar couplings in weakly aligned proteins.

A simple spectral editing procedure is described that generates separate subspectra for the methyl 13C-[1H3] multiplet components of 1H-13C HSQC spectra. The editing procedure relies on co-addition of in-phase and antiphase spectra and yields 1H-coupled constant-time HSQC subspectra for the methyl region that have the simplicity of the regular decoupled CT-HSQC spectrum. Resulting spectra permit rapid and reliable measurement of 1H-13C J and dipolar couplings. The editing procedure is illustrated for a Ca2+-calmodulin sample in isotropic and liquid crystalline phases.

Evaluation of cross-correlation effects and measurement of one-bond couplings in proteins with short transverse relaxation times.

Various strategies are described and compared for measurement of one-bond J(NH) and J(NC') splittings in larger proteins. In order to evaluate the inherent resolution obtainable in the various experiments, relaxation rates of (15)N-(1)H(N) coupled and heteronuclear decoupled resonances were measured at 600- and 800-MHz field strengths for both perdeuterated and protonated proteins. A comparison of decay rates for the two (15)N-¿H(N)¿ doublet components shows average ratios of 4.8 and 3.5 at 800- and 600-MHz (1)H frequency, respectively, in the perdeuterated proteins. For the protonated proteins these ratios are 3.2 (800 MHz) and 2.4 (600 MHz). Relative to the regular HSQC experiment, the enhancement in TROSY (15)N resolution is 2.6 (perdeuterated; 800 MHz), 2.0 (perdeuterated; 600 MHz), 2.1 (protonated; 800 MHz), and 1.7 (protonated; 600 MHz). For the (1)H dimension, the upfield (1)H(N)-¿(15)N¿ component on average relaxes slower than the downfield (1)H(N)-¿(15)N¿ component by a factor of 1.8 (perdeuterated; 800 MHz) and 1.6 (perdeuterated; 600 MHz). The poor resolution for the upfield (15)N-¿(1)H¿ doublet component in slowly tumbling proteins makes it advantageous to derive the J(NH) splitting from the difference in frequency between the narrow downfield (15)N doublet component and either the (1)H-decoupled (15)N resonance or the peak position in an experiment which J-scales the frequency of the upfield doublet component but maintains some of the advantages of the TROSY experiment.

Absolute metabolite quantification by in vivo NMR spectroscopy: IV. Multicentre trial on MRSI localisation tests.

The difference between the experimental and theoretical spatial response function (SRF) of a narrow tube with water is used for a localization test for magnetic resonance spectroscopic imaging (MRSI). From this difference a quantitative performance parameter is derived for the relative amount of signal within a limited region in the field of view. The total signal loss by the MRSI experiment and eddy currents is described by a parameter SL derived from the signal intensities of two echoes. Results of a European multi-centre trial show that this approach is suited for assessment of MRSI localization performance.

Structure and intramodular dynamics of the amino-terminal LIM domain from quail cysteine- and glycine-rich protein CRP2.

Members of the cysteine and glycine-rich protein (CRP) family (CRP1, CRP2, and CRP3) contain two zinc-binding LIM domains, LIM1 and LIM2, and are implicated in diverse cellular processes linked to differentiation, growth control and pathogenesis. The solution structure of an 81-amino acid recombinant peptide encompassing the amino-terminal LIM1 domain of quail CRP2 has been determined by 2D and 3D homo- and heteronuclear NMR spectroscopy. The LIM1 domain consists of two zinc binding sites of the CCHC and the CCCC type, respectively, which both contain two orthogonally arranged antiparallel beta-sheets and which are packed together by a hydrophobic core composed of residues from the zinc finger loop regions. The CCCC zinc finger is followed by a short alpha-helical stretch. The structural analysis revealed that the global fold of LIM1 closely resembles the recently determined solution structures of the carboxyl-terminal LIM2 domains of quail CRP2 and chicken CRP1, and that LIM1 and LIM2 are independently folded structural and presumably functional domains of CRP proteins. To explore the dynamical properties of CRP proteins, we have used 15N relaxation values (T1, T2, and nuclear Overhauser effect (NOE) to describe the dynamical behavior of a LIM domain. A model-free analysis revealed local variations in mobility along the backbone of the quail CRP2 LIM1 motif. Slow motions are evident in turn regions located between the various antiparallel beta-sheets or between their strands. By use of an extended motional model, fast backbone motions were detected for backbone amide NH groups of hydrophobic residues located in the core region of the LIM1 domain. These findings point to a flexible hydrophobic core in the LIM1 domain allowing residual relative mobility of the two zinc fingers, which might be important to optimize the LIM1 interface for interaction with its physiological target molecule(s) and to compensate enthalpically for the entropy loss upon binding.

MR-guided joint puncture and real-time MR-assisted contrast media application.

OBJECTIVE: To develop, in MR arthrography of the shoulder joint, an MR-guided technique for localizing the needle puncture and confirming the intracapsular needle-tip position by visualization of the contrast media inflow. MATERIAL AND METHODS: Three unfixed human shoulder specimens were examined on a 1.0 T MR unit. On the basis of MR-compatible markers, the optimal entrance point for puncturing the joint was determined. The precise localization of the needle tip (MR-compatible 0.7-mm needle) in the shoulder joint was determined with rapid localizer GRE sequences in 2 orthogonal planes. To confirm the intracapsular position of the needle tip, diluted Gd-DTPA was applied via a long connecting tube and contrast medium inflow into the joint space was controlled on an LCD screen in real-time MR imaging (local-look technique). RESULTS: MR-compatible markers on the skin allowed the rapid determination of the optimal entrance point for needle puncture. An adequate localization of the intra-articular needle-tip position was possible in all specimens although significant artifacts were present on rapid localizer GRE sequences which resulted in an increase in the apparent width of the needle shaft. Real-time MR imaging of the contrast medium inflow was made possible by the local-look technique and LCD screen on the MR unit and this allowed confirmation of the intracapsular position. CONCLUSION: In MR arthrography of the shoulder, an MR-guided technique in conjunction with the LCD screen and real-time MR imaging would seem to be a practical alternative to conventional fluoroscopic guidance.

GRASE: ultra-fast turbo gradient spin-echo sequence. A new approach to fast MR imaging of the musculoskeletal system.

PURPOSE: Ultra-fast gradient and spin-echo (GRASE) imaging is a hybrid of turbo spin-echo (TSE) and echo-planar imaging (EPI). One scan consists of several spin echoes (SEs) (turbo factor, TF), each of which consists of a number of gradient echoes (EPI factor, EF). The aim of our study was to evaluate different combinations of TF and EF in GRASE imaging and to test its usefulness in musculoskeletal imaging. MATERIAL AND METHODS: On a 1.0 T MR unit, 11 GRASE sequences with different combinations of TF and EF (TR/TE 2150/120 ms) were evaluated in phantom studies with respect to signal-to-noise (S/N) ratio, nonuniformity of images, and geometrical distortion. From this study, the optimal GRASE-sequence was applied to 25 patients with different joint pathologies and compared to a T2-weighted TSE sequence (TR/TE 2855/130 ms). Lesion visualization, conspicuity, overall image quality, and artifacts were qualitatively analyzed by two observers independently of each other. RESULTS: With respect to S/N ratio, signal nonuniformity, and geometrical distortion, the GRASE sequence with TF/EF 7/3 (S/N 47; signal nonuniformity 11.7%; distortion 1 pixel) proved to be superior to the other GRASE sequences within a scanning time of less than 120 s. In a clinical study, the GRASE sequence proved superior to T2-weighted TSE (without fat suppression) in the visualization of bone-marrow and soft-tissue lesions (p < 0.001) and ligamentous injuries, although the image quality was inferior.

Three-dimensional reconstruction of the liver venous system using the preservation solution as contrast agent.

To investigate whether MRI without using artificial contrast agents can provide sufficient image contrast to visualize the venous tree in the cold stored liver graft, two pig liver grafts were scanned with a multislice turbo spin-echo sequence with long TE (200 msec). The quality of the data obtained at 1-T field strength was sufficient for three-dimensional reconstruction of the hepatic vascular system, potentially useful for liver splitting surgery.

[MRI on low-field tomography systems (0.2 Tesla). A quantitative comparison with equipment of medium-field strength (1.0 Tesla)]. / MRT auf Niederfeldtomographen (0.2 Tesla). Ein quantitativer Vergleich mit einem Gerät mittlerer Feldstärke (1.0 Tesla).

AIM OF THE STUDY: Using phantom studies, a dedicated low-field MR system with 0.2 T and a whole-body MR-scanner with 1.0 T were compared. METHODS: A spin-echo sequence was performed on the 0.2-T MR unit using the knee coil and on the 1.0-T MR unit with the head coil. In a water-filled phantom, signal-to-noise ratios (SNR) were calculated and contrast measurements on gels with well-defined relaxation times were obtained and compared to nominal relaxation times. Measurements of T1 and T2 relaxation times on the low-field system were compared to the 1.0-T unit. As a parameter for geometrical image quality, magnetic field distortions were calculated. In theory, influence of field strength and and receiver bandwidth on the minimal echo time and on chemical shift artifacts were calculated. RESULTS: The SNR was 63.2 on the 0.2-T and 179.6 on the 1.0-T MR unit (difference factor 3, against a theoretical difference of 5-16). Relaxation times on the low-field system were significantly (around 40-50%) lower. Measurements of contrast were similar on both systems. On the low-field system geometrical distortions of several pixels were recorded. The minimal echo time on the low-field system was 21.3 ms with the low receiver bandwidth and 4.3 ms on the 1.0-T MR unit. The amount of chemical shift artefacts was the same on both systems. DISCUSSION: On low-field MR systems SNR is markedly improved by small read-out gradients and a low receiver bandwidth (factor 3 vs 5-16 in comparison with the 1.0-T MR unit). However, an optimal homogeneous magnetic field is required, since inhomogeneities may create severe geometrical distortion.

[MRI-guided MRI arthrography of the shoulder]. / MR-gezielte MR-Arthrographie der Schulter.

PURPOSE: To develop an MR-guided technique for joint puncture in MR arthrography of the shoulder and to confirm the intracapsular position of the needle tip by visualization of the flow of contrast media into the joint. MATERIALS AND METHODS: Three unfixed human shoulder joint specimens were examined on a LOT unit. The optimal point of entrance and depth for joint puncture were estimated by means of MR-compatible markers on the skin. Needle orientation and localization of the needle tip (MR-compatible 22-gauge needle) in the shoulder joint were monitored by rapid localizer gradient-echo sequences in two or thogonal planes. To confirm the intracapsular position of the needle tip, diluted gadolinium-DTPA was administered via a long connecting tube and the flow of contrast media into the joint was viewed directly on an LCD screen using real-time MR imaging (local look technique). RESULTS: The MR-compatible markers on the skin allowed determination of the optimal point of entrance and estimation of the depth for joint puncture. Passive visualization of the MR-compatible needle due to spin dephasing and signal loss provided adequate localization of the intra-articular needle tip position in all specimens, although significant artefacts were present on rapid localizer gradient-echo sequences with an increase in width of the apparent needle shaft. Real-time MR imaging of the flow of contrast media was possible using the local look technique and the LCD screen of the MR unit and allowed confirmation of the intracapsular position. CONCLUSION: MR-guided joint puncture and real-time MR-assisted contrast media application results in improved MR-arthrography and may replace conventional fluoroscopic guidance.

[Ultra-short turbo-spin echo in comparison with turbo-spin echo. Possible applications in the musculoskeletal system]. / Ultrashort-Turbospinecho im Vergleich zu Turbospinecho. Einsatzmöglichkeiten im Muskel-Skelett-System.

Ultrashort turbo spin-echo sequence (TSE) has the advantage of shorter scan times, minimizing motion artifacts, but has the disadvantage of a lower signal-to-noise ratio and suffers from different artifacts. T2-weighted ultrashort TSE (echo train 24) and TSE (echo train 11) were compared in degenerative lesions of the spine (n = 9) and ligamentous lesions associated with sprained ankle injuries (n = 5). The imaging quality of ultrashort TSE was very similar to TSE. There was no difference in diagnostic reliability with ultrashort TSE compared to TSE in the spine or ankle. With regard to contrast properties a higher signal intensity of fatty bone marrow was obtained with ultrashort TSE, with consecutive lower contrast between fluid and edema on the one hand and fatty tissue on the other.