Maître de conférence de l’université d’Orléans
In the present study, we investigated human PEBP1 by NMR to determine the binding site of four different ligands : GTP, FMN, and one Raf-1 peptide in tri-phosphorylated and non-phosphorylated forms. The study was carried out by NMR in near physiological conditions, allowing for the identification of the binding site and the determination of the affinity constants KD for different ligands. Native mass spectrometry was used as an alternative method for measuring KD values. Our study demonstrates and/or confirms the binding of hPEBP1 to the four studied ligands. All of them bind to the same region centered on the conserved ligand-binding pocket of hPEBP1. Although the affinities for GTP and FMN decrease as pH, salt concentration and temperature increase from pH 6.5/NaCl 0 mM/20°C to pH 7.5/NaCl 100 mM/30°C, both ligands clearly do bind under conditions similar to what is found in cells regarding pH, salt concentration and temperature. In addition, our work confirms that residues in the vicinity of the pocket rather than those within the pocket seem to be required for interaction with Raf-1.
We have studied the self-diffusion properties of butyl-methyl-imidazolium bis(trifluoromethylsulfonyl)-imide ([BMIM][TFSI]) + water system. The self-diffusion coefficients of cations, anions, and water molecules were determined by pulsed field gradient NMR. These measures were performed with increased water quantity up to saturation (from 0.3 to 30 mol %). Unexpected variations have been observed. The self-diffusion coefficient of every species increases with the quantity of water but not in the same order of magnitude. Whereas very similar evolutions are observed for the anion and cation, the increase is 25 times greater for water molecules. We interpret our data by the existence of phase separation at microscopic scale.
The phosphatidylethanolamine-binding protein (PEBP) family is widely distributed in various species, from bacteria to mammals. These proteins seem to modulate important cell mechanisms : they control heterotrimeric G-proteins, inhibit the MAP-kinase and NF kappa B signaling pathways, and also serine proteases (thrombin, neuropsin, and chymotrypsin). In order to establish structure-function relationships for this family of proteins, our study focuses on PEBPs expressed within a single organism : Drosophila melanogaster, which constitutes a model system that lends itself well to establishing links between genes’ expression and the corresponding proteins’ functions, and to studying physiological mechanisms such as development.
The solution structure of termicin from hemocytes of the termite Pseudacanthotermes spiniger was determined by proton two-dimensional nuclear magnetic resonance spectroscopy and molecular modeling techniques. Termicin is a cysteine-rich antifungal peptide also exhibiting a weak antibacterial activity. The global fold of termicin consists of an a-helical segment (Phe4-Gln14) and a two-stranded (Phe19-Asp25 and Gln28-Phe33) antiparallel. ß-sheet forming a "cysteine stabilized aß motif" (CSaß) also found in antibacterial and antifungal defensins from insects and from plants.
PA1b (pea albumin 1, subunit b) is a 37-amino acid cysteine-rich plant defense protein isolated from pea seeds (Pisum sativum). It induces short-term mortality in several pests, among which the cereal weevils Sitophilus sp. (Sitophilus oryzae, Sitophilus granarius, and Sitophilus zeamais) that are a major nuisance for stored cereals, all over the world.
To elucidate the low proton nuclear magnetic resonance (NMR) visibility of muscle lactate previously demonstrated in excised rat muscle, lactate transverse relaxation was investigated in, the same model using double quantum editing sequences with effective echo times ranging from 55 to 475 msec. On this time scale, muscle lactate clearly exhibits a bi-exponential transverse relaxation with a short T-2 of 33 +/- 5 msec (mean +/- SE, n = 3) and a long T-2 of 230 +/- 10 msec. The relative populations (84 +/- 4% vs. 16 +/- 4%, respectively) of these two lactate pools are compatible with compartmentation between intra- and extracellular muscle lactate. Magn Reson Med 41:624-626, 1999. (C) 1999 Wiley-Liss, Inc.
A novel approach is presented that combines NR IR-plethysmography and NMRS of deoxymyoglobin in real-time, using line-by-line interleaved acquisitions of both gradient echo images during venous occlusion and of the N-delta proton signal of myoglobin’s proximal F8 histidine, This method allowed simultaneous measurement of peripheral regional perfusion and skeletal muscle oxygen content. During reactive hyperaemia, using our combined NMRI-NMRS protocol, we explored the relationship between muscle reoxygenation (myoglobin resaturation half-time, y in s) and reperfusion (x in ml/100 g tissue/min) and found it to be highly significant (y = 70.83x (-0.94) ; r(2) = 0.70 ; F = 64.40 ; p = 9.73 x 10(-9)).
Lactate NMR visibility was investigated in excised rat muscle at 3 T by comparing the concentration determined in situ by double quantum (DQ) proton spectroscopy (150 ms effective echo time) to the concentration measured in vitro from perchloric acid extracts of the same muscle samples, After 1-2 h of ischemia, lactate NMR visibility was 32 +/- 3% (+/-SE, n = 9), and was only 21 +/- 1% (n = 6) after 10-12 h. Muscle lactate T-2 was 140 +/- 11 ms and 184 +/- 6 ms, respectively. All potential mechanisms of DQ lactate signal attenuation (B-0 and B-1 inhomogeneity, DQ transverse relaxation, diffusion) were examined, and accounted for when necessary. A significant increase in lactate NMR visibility was demonstrated using a shorter effective echo time (79 ms) DQ editing sequence. These results are interpreted as reflecting muscle lactate compartmentation between a long T-2 pool predominantly detected by DQ spectroscopy, and a short T-2 pool virtually invisible with longer echo time NMR techniques.
Novel tools are presented that aim at more comprehensive NMR investigations of human skeletal muscle metabolism, in particular during exercise protocols. They integrate imaging (NMRI) and spectroscopy (NMRS) experiments in a single dynamic examination. The first. sequence that we propose combines NMR-plethysmography, H-1-NMRS of deoxymyoglobin and P-31-NMRS.
The classical double-quantum editing sequence 90 degrees(x)-tau-180 degrees(y)-tau-90 degrees(x)-t(1)-90 degrees(x)-tau-180 degrees(y)-tau-AQ (tau = 1/4J) was rendered volume selective, by making slice selective the first 90 degrees pulse and the two 180 degrees pulses, Using simple rules to ensure optimum radio frequency phase coherence, this single-voxel editing sequence, reminiscent of a basic PRESS localization technique, was implemented on a whole-body 3 T spectrometer, and in vitro editing of lactate methyl protons was demonstrated without any significant loss in intrinsic sensitivity, The effectiveness of the proposed approach in vivo was also illustrated through the localized monitoring of lactate in the human leg during and after exercise.
In vivo NMR evidence for moderate glucose accumulation in human skeletal muscle during hyperglycemia. Am. J. Physiol. 271 (Endocrinol. Metab. 34) : E434-E438, 1996.-Although the absence of intracellular (IC) free glucose is direct evidence of glucose transport being the rate-limiting step for muscle glucose disposal at euglycemia, the scarcity of data in humans during hyperglycemia precludes any definitive conclusion. In the present study, C-13 and P-31 in vivo nuclear magnetic resonance (NMR) data from two separate groups of subjects were combined to measure IC free glucose in the human skeletal muscle. When these noninvasive tools were used with an infusion of [1-C-13]glucose, a steady-state concentration of 1.2 +/- 0.2 mmol IC glucose/l IC water was observed at the end of a 2-h hyperglycemic clamp with somatostatin infusion, during which glycemia was maintained at approximate to 22 mmol/l and insulinemia at approximate to 5 mU/l. Despite this moderate glucose accumulation, the persistence of a large transmembrane glucose gradient suggests that the posttransport steps do not play a significant role in the control of muscle glucose disposal in these specific conditions, relevant to insulinopenic diabetic patients.
H-1 NMR simultaneous editing of C-13-coupled and C-13-uncoupled methyl protons resonance, using the selection of double quantum coherences by a gradient pulse, was analyzed in vitro and demonstrated in situ on the hindlimb of an exercised rat model postmortem. In vitro calibration showed agreement with theoretical analysis. High-resolution NMR of muscle extract confirmed the accuracy of the lactate C-13-enrichment calculated using the in situ NMR data and the calibration factor obtained in vitro.