Production of stable isotope labelled lipase Lip2 from Yarrowia lipolytica for NMR: investigation of several expression systems

Extracellular lipase Lip2 from Yarrowia lipolytica is a promising biocatalyst with unusual structural features, as indicated by X-ray crystallography. These features comprise a mobile domain called the lid that controls access to the catalytic site. Conformational rearrangements of the lid have been suggested to regulate lipase enzymatic activities. We used nuclear magnetic resonance to investigate the dynamics of Lip2 by exploring four expression systems, Escherichia coli, cell-free, Pichia pastoris and Y. lipolytica to produce uniformly labelled enzyme. The expression of Lip2 was assessed by determining its specific activity and measuring (15)N-(1)H HSQC spectra. Y. lipolytica turned out to be the most efficient expression system. Here, we report the first use of Y. lipolytica as an expression host for the production of uniform stable isotopic labelled protein for further structural and dynamics studies using NMR.

Study of the specific lipid binding properties of Abeta 11-22 fragment at endosomal pH

Increasing evidence implicates interactions between Abeta peptide and lipids in the development of Alzheimer's disease. More generally, Abeta peptide interactions with membranes seem to depend on the composition of the lipid bilayer and the structural features of the peptide. One key parameter should be pH, since one site of intracellular Abeta peptide production and/or accumulation is likely to be endosomes. This intracellular endosomal accumulation was suggested to contribute to disease progression. In this paper, we report a study on the 11-22 amphiphilic domain of Abeta in interaction with model membrane; this region contains most of the charged residues of the N-terminal domain of Abeta. We show that the peptide charge, and more precisely the protonation state of histidines 13 and/or 14, is important for the interaction with lipids. Hence, it is only at endosomal pH that a conformational change of the peptide is observed in the presence of negatively charged lipid vesicles, that is, when both lipid headgroups and histidines can interact through electrostatic interactions. Specific interactions of the fragment with phosphatidylserine and to a lesser extent with phosphatidylcholine, but not phosphatidylethanolamine, are further evidenced by the Langmuir monolayer technique. From our results, we suggest that the protonation state of His residues could have a role in the pathogenic surface interaction of the whole Abeta peptide with membranes.

Detection of natural abundance 1H-13C correlations of cholesterol in its membrane environment using a gradient enhanced HSQC experiment under high resolution magic angle spinning

The quality and signal to noise ratio of a J-based HETCOR performed on a standard MAS probe have been compared with a gradient enhanced HSQC performed on a HR-MAS probe at 500 MHz. The sample selected was cholesterol, inserted at 30 mol% in acyl chain deuterated phospholipids (DMPC-d54), at a temperature where the bilayer is in a liquid crystalline phase (310 K). It is representative of any rigid molecule undergoing fast axial diffusion in a bilayer as the main movement. After optimization of the spinning rate and carbon decoupling conditions, it is shown that the ge-HSQC/MAS approach is far superior to the more conventional J-HETCOR/MAS in terms of signal to noise ratio, and that it allows the detection of all the natural abundance cross peaks of cholesterol in a membrane environment. Clear differences between the 1H and 13C chemical shifts of cholesterol in a membrane and in chloroform solution were thus revealed.

High resolution 13C NMR spectra on oriented lipid bilayers: from quantifying the various sources of line broadening to performing 2D experiments with 0.2-0.3 ppm resolution in the carbon dimension

13C NMR spectra routinely performed on oriented lipid bilayers display linewidth of 1-2 ppm, although T2 measurements indicate that 0.1-0.2 ppm could be obtained. We have prepared a DMPC-13C4-cholesterol (7/3) sample, and oriented the lipid bilayers between glass plates so that the bilayer normal makes an angle of 90 degrees (or of the magic angle) with Bo. We have measured T2s, CSAs, and linewidths for the choline 13C-gamma-methyl, the cholesterol-C4 carbons and the lipid head group phosphorus, at both angles and 313 K. The magnetic field distribution within the sample was calculated using the surface current formalism. The line shapes were simulated as a function of Bo field inhomogeneities and sample mosaic spread. Both effects contribute to the experimental linewidth. Using three signals of different CSA, we have quantified both contributions and measured the mosaic spread accurately. Direct shimming on a sample signal is essential to obtain sharp resonances and 13C labelled choline methyl resonance of DMPC is a good candidate for this task. After optimisation of the important parameters (shimming on the choline resonance, mosaic spread of +/-0.30 degrees), 13C linewidth of 0.2-0.3 ppm have been obtained. This newly achieved resolution on bilayers oriented at 90 degrees, has allowed to perform two 2D experiments, with a good sensitivity: 2D PELF (correlation of carbon chemical shifts and C-H dipolar couplings) and 2D D-resolved experiment (correlation of carbon chemical shifts and C-C dipolar couplings). A C-C dipolar coupling of 35 +/- 2 Hz between the choline methyl carbons was determined.

Organization and dynamics of the proteolipid complexes formed by annexin V and lipids in planar supported lipid bilayers

The consequences of the binding of annexin V on its lateral mobility and that of lipids were investigated by means of experimental and simulated FRAP experiments. Experiments were carried out on planar supported bilayers (PC/PS 9:1 mol/mol mixtures) in the presence of 1 mM CaCl2 in the subphase. The probes C12-NBD-PS and fluorescein-labeled annexin V were used and the data compared with that previously obtained for C12-NBD-PC [Saurel, O., Cézanne, L., Milon, A., Tocanne, J. F., & Demange, P. (1998) Biochemistry 37, 1403-1410]. At complete coverage of the lipid bilayer by the protein (Cannexin = 80 nM), the lateral mobility of C12-NBD-PC was reduced by 40% while C12-NBD-PS and bound annexin V molecules were nearly immobilized (D < 10(-)11 cm2/s). At moderate protein concentration (20 nM < Cannexin < 80 nM), best fitting of the lipid and protein probe recoveries was achieved with one single diffusion coefficient and a mobile fraction close to 100%, indicating homogeneous lipid and protein populations. In contrast, at low protein concentration (Cannexin < 20 nM), C12-NBD-PS showed a two-component diffusion. The slow PS population at Cannexin < 20 nM and the single PS population at Cannexin > 20 nM moved at the same rate that bound annexin V (mobile fraction close to 100%), indicating strong PS/protein interactions. With the aid of computer simulations of the lateral motion of PC molecules, based on the 2-D crystalline networks formed by annexin V in contact with the lipid bilayer, these FRAP results may be accounted for by considering a rather simple model of a proteolipidic complex consisting of an extended 2-D crystalline protein network facing the lipid bilayer and stabilized by strong interactions between annexin V and PS molecules. In this model, immobilization of annexin V and PS molecules originates from their mutual interactions. The slowing down of PC molecules is due to various obstacles to their lateral diffusion which can be described as: the four PS molecules bound to the protein, the tryptophan 187 which presumably interacts with the lipids at the level of their polar headgroups and probably the three other hydrophobic amino acid residues located on the AB calcium-binding loops of the protein.

Influence of annexin V on the structure and dynamics of phosphatidylcholine/phosphatidylserine bilayers: a fluorescence and NMR study

The consequences of the binding of annexin V on the structure and dynamics of PC/PS bilayers were studied by means of fluorescence polarization, 31P NMR, 2H NMR, and fluorescence recovery after photobleaching (FRAP). Even at complete coverage of the lipid bilayers by the protein, annexin V showed no influence on the lipid molecular packing and the acyl chain flexibility of both PC and PS. The fluorescence polarization of the probe DPH, the 31P NMR spectra, and deuterium quadrupolar splittings of P(d31)OPS remained unchanged. However, upon binding of annexin V, two distinct populations of PC were visible in 2H NMR, which were in slow exchange on the deuterium NMR time scale (microseconds). One component in the spectrum was identical to the protein-free sample, while a second, broad, component appeared. The presence of the protein induced a decrease in the transverse relaxation times (T2e), indicative of the appearance of slow motions (milliseconds to microseconds), in the P(d31)-OPS spectrum and in the P(d31)OPC broad component. FRAP experiments were carried out with the probes C12-NBD-PC and C12-NBD-PS: at saturation, annexin V reduced the lateral diffusion rate of PC by 40% and nearly blocked the diffusion of PS. These combined experiments are consistent with a model in which annexin V enters a proteolipidic complex in the form of an extended 2D network, stabilized by specific interactions with PS. As seen from the lateral diffusion rates and the acyl chains NMR spectral parameters, two separate lipid populations appear, presumably corresponding to those interacting with annexinV (PC and PS) and protein free domains (mainly PC).