Remote detection of nuclear magnetic resonance with an anisotropic magnetoresistive sensor.

We report the detection of nuclear magnetic resonance (NMR) using an anisotropic magnetoresistive (AMR) sensor. A "remote-detection" arrangement was used in which protons in flowing water were prepolarized in the field of a superconducting NMR magnet, adiabatically inverted, and subsequently detected with an AMR sensor situated downstream from the magnet and the adiabatic inverter. AMR sensing is well suited for NMR detection in microfluidic "lab-on-a-chip" applications because the sensors are small, typically on the order of 10 mum. An estimate of the sensitivity for an optimized system indicates that approximately 6 x 10(13) protons in a volume of 1,000 mum(3), prepolarized in a 10-kG magnetic field, can be detected with a signal-to-noise ratio of 3 in a 1-Hz bandwidth. This level of sensitivity is competitive with that demonstrated by microcoils in superconducting magnets and with the projected sensitivity of microfabricated atomic magnetometers.

Solution NMR studies of the integral membrane proteins OmpX and OmpA from Escherichia coli.

Membrane proteins are usually solubilized in polar solvents by incorporation into micelles. Even for small membrane proteins these mixed micelles have rather large molecular masses, typically beyond 50000 Da. The NMR technique TROSY (transverse relaxation-optimized spectroscopy) has been developed for studies of structures of this size in solution. In this paper, strategies for the use of TROSY-based NMR experiments with membrane proteins are discussed and illustrated with results obtained with the Escherichia coli integral membrane proteins OmpX and OmpA in mixed micelles with the detergent dihexanoylphosphatidylcholine (DHPC). For OmpX, complete sequence-specific NMR assignments have been obtained for the polypeptide backbone. The 13C chemical shifts and nuclear Overhauser effect data then resulted in the identification of the regular secondary structure elements of OmpX/DHPC in solution, and in the collection of an input of conformational constraints for the computation of the global fold of the protein. For OmpA, the NMR assignments are so far limited to about 80% of the polypeptide chain, indicating different dynamic properties of the reconstituted OmpA beta-barrel from those of OmpX. Overall, the present data demonstrate that relaxation-optimized NMR techniques open novel avenues for studies of structure, function and dynamics of integral membrane proteins.

Method for accurate measurements of nuclear-spin optical rotation for applications in correlated optical-NMR spectroscopy.

The nuclear-spin optical rotation (NSOR) effect recently attracted much attention due to potential applications in combined optical-NMR spectroscopy and imaging. Currently, the main problem with applications of NSOR is low SNR and accuracy of measurements. In this work we demonstrate a new method for data acquisition and analysis based on a low-power laser and an emphasis on software based processing. This method significantly reduces cost and is suitable for application in most NMR spectroscopy laboratories for exploration of the NSOR effect. Despite the use of low laser power, SNR can be substantially improved with fairly simple strategies including the use of short wavelength and a multi-pass optical cell with in-flow pre-polarization in a 7 T magnet. Under these conditions, we observed that NSOR signal can be detected in less than 1 min and discuss strategies for further improvement of signal. With higher SNR than previously reported, NSOR constants can be extracted with improved accuracy. On the example of water, we obtained measurements at a level of accuracy of 5%. We include a detailed theoretical analysis of the geometrical factors of the experiment, which is required for accurate quantification of NSOR. This discussion is particularly important for relatively short detection cells, which will be necessary to use in spectroscopy or imaging applications that impose geometrical constraints.

Facilitated substrate transport through membrane proteins.

Substrate transport through the membrane protein maltoporin is facilitated by an affinity site in the channel. The analysis of the ion current fluctuations induced by penetration of the sugar into the channel yields the kinetic constants. Modification of the affinity site by replacing the aromatic residues suggests that nature has optimized the channel protein for maximum affinity at the extracellular side, as well as for an increased off-rate to eject a sugar trapped in the pore towards the periplasmic side.

Controlling membrane permeability with bacterial porins: application to encapsulated enzymes.

Recent achievements of membrane protein science allow easy protein modification by genetic engineering and, for some proteins, their production in large quantities. We regard these features as the basic requirements for applications of membrane proteins in materials science. Here, we demonstrate a possible application of membrane proteins, inserting porins from the outer cell wall of Escherichia coli into the walls of liposomes. Encapsulation of enzymes into liposomes or polymer nanocapsules protects them against proteases and denaturation. Functional reconstitution of porins into the capsule shell allows to control the rate and selectivity of substrate permeation, and thus to control the enzyme reaction kinetics. We suggest that this technique can prove to be useful in the area of biosensors, providing enzymatic stability while keeping the functionality or even enhancing the sensitivity by substrate preselection. Another application of this kind of stabilisation is in the field of single enzyme activity recording.

Altered diurnal rhythm of prolactin in systemic sclerosis.

OBJECTIVE: Mild hyperprolactinemia has been reported in systemic lupus erythematosus (SLE) and systemic sclerosis (SSc). We investigated whether the elevated serum level of prolactin (Prl) detected in SSc is due to a sustained increase over 24 h and/or a shift in the diurnal rhythm, and whether Prl autoantibodies--originally described in SLE--may interfere in the assay. METHODS: The serum level of Prl was measured by ELISA and compared between 73 patients with SSc and 73 age and sex matched controls (78% women, age 56 +/- 11 years). The diurnal rhythms of Prl and thyrotropin (thyroid stimulating hormone, TSH) were compared between 3 patients with SSc and 10 healthy controls. Blood was taken at 2-3, 6-7, 10-11 a.m., and 2-3, 6-7, 10-11 p.m. The serum level of Prl autoantibodies was measured by ELISA and compared between matched patients with SSc and SLE and controls (n = 42 each). Standard curves of the Prl ELISA were spiked with 10% sera containing high levels of Prl autoantibodies to test interference. RESULTS: Serum levels of Prl measured in the morning (8-10 a.m.) were significantly higher in patients with SSc (17.9 +/- 7.7 ng/ml), compared with controls (9.3 +/- 4.2 ng/ml; p < 0.05). In SSc, 40% of patients had Prl levels > 20 ng/ml, but no correlation was found with Scl-70 or Prl autoantibodies. Younger patients (< 50 years, n = 23/73) showed higher serum levels of Prl than older patients (21.3 +/- 10.3 vs 16.3 +/- 6.2 ng/ml; p < 0.05). The diurnal rhythm of Prl revealed that both a sustained increase over 24 h and some shift occurred in SSc. Peaks of secretion were detected between 6 and 11 a.m., instead of 2-6 a.m. The median levels of TSH over 24 h in patients with SSc ranged within the normal limits. Nevertheless, in SSc, a significant correlation (r = 0.59, p < 0.01) was found between diurnal rhythms of Prl and TSH. The prevalence of Prl autoantibodies in serum was 8% in SSc, 27% in SLE, and < 5% in controls. However, the presence of Prl autoantibodies did not interfere with our assay. CONCLUSION: Our data confirm that mild hyperprolactinemia occurs in a subgroup of patients with SSc, and showed that the elevated serum level of Prl is due to both a sustained increase over 24 h and a shift in the diurnal rhythm. The correlation between diurnal rhythms of Prl and TSH suggests common regulatory mechanisms.

Macrophage Activation Factorsin the Brains of AIDS Patients.

HIV, soluble HLA class I (sHLA-I), quinolinic acid (QUIN), and the monokines IL-1β, IL-6, and TNF-α were measured by ELISA and PCR in brain tissue of 60 AIDS autopsies without evidence of CNS opportunistic infections. Individual cases showed good interrogational correlations for the factors measured. There was a positive correlation between concentrations of IL-1β and IL-6. Brain viral burden correlated with intraparenchymal levels of sHLA-I, IL-1β, and IL-6. Comparison of neuritic damage and levels of immune mediators implicates macrophage activation factors in the etiology of neurologic damage in AIDS.