The accuracy limit of chemical shift predictions for species in aqueous solution.

Interpreting NMR experiments benefits from first-principles predictions of chemical shifts. Reaching the accuracy limit of theory is relevant for unambiguous structural analysis and dissecting theoretical approximations. Since accurate chemical shift measurements are based on using internal reference compounds such as trimethylsilylpropanesulfonate (DSS), a detailed comparison of experimental with theoretical data requires simultaneous consideration of both target and reference species ensembles in the same solvent environment. Here we show that ab initio molecular dynamics simulations to generate liquid-state ensembles of target and reference compounds, including explicitly their short-range solvation environments and combined with quantum-mechanical solvation models, allows for predicting highly accurate 1H (∼0.1-0.5 ppm) and aliphatic 13C (∼1.5 ppm) chemical shifts for aqueous solutions of the model compounds trimethylamine N-oxide (TMAO) and N-methylacetamide (NMA), referenced to DSS without any system-specific adjustments. This encompasses the two peptide bond conformations of NMA identified by NMR. The results are used to derive a general-purpose guideline set for predictive NMR chemical shift calculations of NMA in the liquid state and to identify artifacts of force field models. Accurate predictions are only obtained if a sufficient number of explicit water molecules is included in the quantum-mechanical calculations, disproving a purely electrostatic model of the solvent effect on chemical shifts.

NMR derived changes of lipoprotein particle concentrations related to impaired fasting glucose, impaired glucose tolerance, or manifest type 2 diabetes mellitus.

BACKGROUND: Type 2 diabetes mellitus (T2D) and corresponding borderline states, impaired fasting glucose (IFG) and/or glucose tolerance (IGT), are associated with dyslipoproteinemia. It is important to distinguish between factors that cause T2D and that are the direct result of T2D. METHODS: The lipoprotein subclass patterns of blood donors with IFG, IGT, with IFG combined with IGT, and T2D are analyzed by nuclear magnetic resonance (NMR) spectroscopy. The development of lipoprotein patterns with time is investigated by using samples retained for an average period of 6 years. In total 595 blood donors are classified by oral glucose tolerance test (oGTT) and their glycosylated hemoglobin (HbA1c) concentrations. Concentrations of lipoprotein particles of 15 different subclasses are analyzed in the 10,921 NMR spectra recorded under fasting and non-fasting conditions. The subjects are assumed healthy according to the strict regulations for blood donors before performing the oGTT. RESULTS: Under fasting conditions manifest T2D exhibits a significant concentration increase of the smallest HDL particles (HDL A) combined with a decrease in all other HDL subclasses. In contrast to other studies reviewed in this paper, a general concentration decrease of all LDL particles is observed that is most prominent for the smallest LDL particles (LDL A). Under normal nutritional conditions a large, significant increase of the concentrations of VLDL and chylomicrons is observed for all groups with IFG and/or IGT and most prominently for manifest T2D. As we show it is possible to obtain an estimate of the concentrations of the apolipoproteins Apo-A1, Apo-B100, and Apo-B48 from the NMR data. In the actual study cohort, under fasting conditions the concentrations of the lipoproteins are not increased significantly in T2D, under non-fasting conditions only Apo-B48 increases significantly. CONCLUSION: In contrast to other studies, in our cohort of "healthy" blood donors the T2D associated dyslipoproteinemia does not change the total concentrations of the lipoprotein particles produced in the liver under fasting and non-fasting conditions significantly but only their subclass distributions. Compared to the control group, under non-fasting conditions participants with IGT and IFG or T2D show a substantial increase of plasma concentrations of those lipoproteins that are produced in the intestinal tract. The intestinal insulin resistance becomes strongly observable.

Reactivity of Cu(I) Nacnac Complexes Toward Polypnictogen Compounds.

The nacnac Cu(I) compound [LCu(MeCN)] (2) (L = [{N(C6H3Me2-2,6)C(Me)}2CH]-) was reacted with complexes containing aromatic cyclo-E5 ([Cp*Fe(η5-E5)], E = P (1a), As (1b), Cp* = η5-C5Me5), cyclo-P4 ([Cp‴Co(η4-P4)] (3), Cp‴ = η5-C5H2tBu3) and cyclo-E3 ligands ([Cp‴Ni(η3-E3)], E = P (4a), As (4b)) yielding the heterometallic complexes [(Cp*Fe)(µ,η5:2-E5)(LCu)] (E = P (5a), As (5b)), [(Cp*Fe)(µ3,η5:2:1-E5)(LCu)2] (E = P (6a), As (6b)), [(Cp‴Co)(µ,η4:2-P4)(LCu)] (7), [(Cp‴Co)(µ3,η4:2:1-P4)(LCu)2] (8), and [(Cp‴Ni)(µ,η3:2-E3)(LCu)] (E = P (9a), As (9b)). These complexes are rare examples of the coordination of a group 11 metal to aromatic cyclo-En (E = P, As; n = 3-5) ligands. All products were comprehensively characterized by crystallographic and spectroscopic methods. Their dynamic behavior in solution was studied by VT (variable-temperature) NMR spectroscopy, and their electronic structures were elucidated by DFT calculations.

Au-Containing Coordination Polymers Based on Polyphosphorus Ligand Complexes.

Whereas the self-assembly of pentaphosphaferrocenes [CpRFe(η5-P5)] (CpR = Cp*, Cp×, and CpBn) with Cu and Ag salts has been well-studied in the past, the coordination chemistry toward Au complexes has been left untouched so far. Herein, the results of the self-assembly processes of [CpRFe(η5-P5)] with Au salts of different anions (GaCl4-, SbF6-, and Al(OC(CF3)3)4 (TEF-)) are reported. Next to a variety of molecular coordination products, the first coordination polymers based on polyphosphorus ligand complexes and Au salts are also obtained. Thereby, a 2D coordination polymer comprising metal vacancies is isolated. In all products, the Au centers are coordinated in a linear or a trigonal planar environment. In solution, highly dynamic processes are observed. Variable-temperature NMR spectroscopy, solid-state NMR spectroscopy, and X-ray powder diffraction were applied to gain further insight into selected coordination compounds.

Three-Component Self-Assembly Changes its Course: A Leap from Simple Polymers to 3D†Networks of Spherical Host-Guest Assemblies.

One-pot self-assembly reactions of the polyphosphorus complex [Cp*Fe(η5 -P5 )] (A), a coinage metal salt AgSbF6 , and flexible aliphatic dinitriles NC(CH2 )x CN (x=1-10) yield 1D, 2D, and 3D coordination polymers. The seven-membered backbone of the dinitrile was experimentally found as the borderline for the self-assembly system furnishing products of different kinds. At x<7, various rather simple polymers are exclusively formed possessing either 0D or 1D Ag/A structural motifs connected by dinitrile spacers, while at x≥7, the self-assembly switches to unprecedented extraordinary 3D networks of nano-sized host-guest assemblies (SbF6 )@[(A)9 Ag11 ]11+ (x=7) or (A)@[(A)12 Ag12 ]12+ (x=8-10) linked by dinitriles. The polycationic nodes represent the first superspheres based on A and silver and are host-guest able. All products are characterized by NMR spectroscopy, mass spectrometry, and single-crystal X-ray diffraction. The assemblies [(A)12 Ag12 ]12+ were visualized by transmission electron microscopy.

A suite of 19F based relaxation dispersion experiments to assess biomolecular motions.

Proteins and nucleic acids are highly dynamic bio-molecules that can populate a variety of conformational states. NMR relaxation dispersion (RD) methods are uniquely suited to quantify the associated kinetic and thermodynamic parameters. Here, we present a consistent suite of 19F-based CPMG, on-resonance R1ρ and off-resonance R1ρ RD experiments. We validate these experiments by studying the unfolding transition of a 7.5 kDa cold shock protein. Furthermore we show that the 19F RD experiments are applicable to very large molecular machines by quantifying dynamics in the 360 kDa half-proteasome. Our approach significantly extends the timescale of chemical exchange that can be studied with 19F RD, adds robustness to the extraction of exchange parameters and can determine the absolute chemical shifts of excited states. Importantly, due to the simplicity of 19F NMR spectra, it is possible to record complete datasets within hours on samples that are of very low costs. This makes the presented experiments ideally suited to complement static structural information from cryo-EM and X-ray crystallography with insights into functionally relevant motions.

Correction to: A suite of 19F based relaxation dispersion experiments to assess biomolecular motions.

In the original publication, Figures 3 and 6 were displayed incorrectly due to a mistake made by the publisher. The correct version of Figs. 3 and 6 are given below.

Pressure dependence of side chain 1H and 15N-chemical shifts in the model peptides Ac-Gly-Gly-Xxx-Ala-NH2.

For interpreting the pressure induced shifts of resonance lines of folded as well as unfolded proteins the availability of data from well-defined model systems is indispensable. Here, we report the pressure dependence of 1H and 15N chemical shifts of the side chain atoms in the protected tetrapeptides Ac-Gly-Gly-Xxx-Ala-NH2 (Xxx is one of the 20 canonical amino acids) measured at 800 MHz proton frequency. As observed earlier for other nuclei the chemical shifts of the side chain nuclei have a nonlinear dependence on pressure in the range from 0.1 to 200 MPa. The pressure response is described by a second degree polynomial with the pressure coefficients B1 and B2 that are dependent on the atom type and type of amino acid studied. A number of resonances could be assigned stereospecifically including the 1H and 15N resonances of the guanidine group of arginine. In addition, stereoselectively isotope labeled SAIL amino acids were used to support the stereochemical assignments. The random-coil pressure coefficients are also dependent on the neighbor in the sequence as an analysis of the data shows. For Hα and HN correction factors for different amino acids were derived. In addition, a simple correction of compression effects in thermodynamic analysis of structural transitions in proteins was derived on the basis of random-coil pressure coefficients.

Iodination of cyclo-E5 -Complexes (E=P, As).

In a high-yield one-pot synthesis, the reactions of [Cp*M(η5 -P5 )] (M=Fe (1), Ru (2)) with I2 resulted in the selective formation of [Cp*MP6 I6 ]+ salts (3, 4). The products comprise unprecedented all-cis tripodal triphosphino-cyclotriphosphine ligands. The iodination of [Cp*Fe(η5 -As5 )] (6) gave, in addition to [Fe(CH3 CN)6 ]2+ salts of the rare [As6 I8 ]2- (in 7) and [As4 I14 ]2- (in 8) anions, the first di-cationic Fe-As triple decker complex [(Cp*Fe)2 (µ,η5:5 -As5 )][As6 I8 ] (9). In contrast, the iodination of [Cp*Ru(η5 -As5 )] (10) did not result in the full cleavage of the M-As bonds. Instead, a number of dinuclear complexes were obtained: [(Cp*Ru)2 (µ,η5:5 -As5 )][As6 I8 ]0.5 (11) represents the first Ru-As5 triple decker complex, thus completing the series of monocationic complexes [(CpR M)2 (µ,η5:5 -E5 )]+ (M=Fe, Ru; E=P, As). [(Cp*Ru)2 As8 I6 ] (12) crystallizes as a racemic mixture of both enantiomers, while [(Cp*Ru)2 As4 I4 ] (13) crystallizes as a symmetric and an asymmetric isomer and features a unique tetramer of {AsI} arsinidene units as a middle deck.

1H NMR spectroscopy quantifies visibility of lipoproteins, subclasses, and lipids at varied temperatures and pressures.

NMR-based quantification of human lipoprotein (sub)classes is a powerful high-throughput method for medical diagnostics. We evaluated select proton NMR signals of serum lipoproteins for elucidating the physicochemical features and the absolute NMR visibility of their lipids. We separated human lipoproteins of different subclasses by ultracentrifugation and analyzed them by 1H NMR spectroscopy at different temperatures (283-323 K) and pressures (0.1-200 MPa). In parallel, we determined the total lipid content by extraction with chloroform/methanol. The visibility of different lipids in the 1H NMR spectra strongly depends on temperature and pressure: it increases with increasing temperatures but decreases with increasing pressures. Even at 313 K, only part of the lipoprotein is detected quantitatively. In LDL and in HDL subclasses HDL2 and HDL3, only 39%, 62%, and 90% of the total cholesterol and only 73%, 70%, and 87% of the FAs are detected, respectively. The choline head groups show visibilities of 43%, 75%, and 87% for LDL, HDL2, and HDL3, respectively. The description of the NMR visibility of lipid signals requires a minimum model of three different compartments, A, B, and C. The thermodynamic analysis of compartment B leads to melting temperatures between 282 K and 308 K and to enthalpy differences that vary for the different lipoproteins as well as for the reporter groups selected. In summary, we describe differences in NMR visibility of lipoproteins and variations in biophysical responses of functional groups that are crucial for the accuracy of absolute NMR quantification.

Dicationic E4 Chains (E=P, As, Sb, Bi) Embedded in the Coordination Sphere of Transition Metals.

The oxidation chemistry of the complexes [{CpMo(CO)2 }2 (µ,η2 :η2 -E2 )] (E=P (A), As (B), Sb (C), Bi (D)) is compared. The oxidation of A-D with [Thia]+ (=[C12 H8 S2 ]+ ) results in the selective formation of the dicationic E4 complexes [{CpMo(CO)2 }4 (µ4 ,η2 :η2 :η2 :η2 -E4 )]2+ (E=P (1), As (2), Sb (3), Bi (4)), stabilized by four [CpMo(CO)2 ] fragments. The formation of the corresponding monocations [A]+ , [C]+ , and [D]+ could not be detected by cyclic voltammetry, EPR, or NMR spectroscopy. This finding suggests that dimerization is fast and that there is no dissociation in solution, which was also predicted by DFT calculations. However, EPR measurements of 2 confirmed the presence of small amounts of the radical cation [B]+ in solution. Single-crystal X-ray diffraction revealed that the products 1 and 2 feature a zigzag E4 chain in the solid state while 3 and 4 bear a central E4 cage with a distorted "butterfly-like" geometry. Additionally, 1 can be easily and reversibly converted into a symmetric and an unsymmetric form.

Pressure dependence of side chain 13C chemical shifts in model peptides Ac-Gly-Gly-Xxx-Ala-NH2.

For evaluating the pressure responses of folded as well as intrinsically unfolded proteins detectable by NMR spectroscopy the availability of data from well-defined model systems is indispensable. In this work we report the pressure dependence of 13C chemical shifts of the side chain atoms in the protected tetrapeptides Ac-Gly-Gly-Xxx-Ala-NH2 (Xxx, one of the 20 canonical amino acids). Contrary to expectation the chemical shifts of a number of nuclei have a nonlinear dependence on pressure in the range from 0.1 to 200 MPa. The size of the polynomial pressure coefficients B 1 and B 2 is dependent on the type of atom and amino acid studied. For HN, N and Cα the first order pressure coefficient B 1 is also correlated to the chemical shift at atmospheric pressure. The first and second order pressure coefficients of a given type of carbon atom show significant linear correlations suggesting that the NMR observable pressure effects in the different amino acids have at least partly the same physical cause. In line with this observation the magnitude of the second order coefficients of nuclei being direct neighbors in the chemical structure also are weakly correlated. The downfield shifts of the methyl resonances suggest that gauche conformers of the side chains are not preferred with pressure. The valine and leucine methyl groups in the model peptides were assigned using stereospecifically 13C enriched amino acids with the pro-R carbons downfield shifted relative to the pro-S carbons.

High pressure 31P NMR spectroscopy on guanine nucleotides.

The 31P NMR pressure response of guanine nucleotides bound to proteins has been studied in the past for characterizing the pressure perturbation of conformational equilibria. The pressure response of the 31P NMR chemical shifts of the phosphate groups of GMP, GDP, and GTP as well as the commonly used GTP analogs GppNHp, GppCH2p and GTPγS was measured in the absence and presence of Mg2+-ions within a pressure range up to 200 MPa. The pressure dependence of chemical shifts is clearly non-linear. For all nucleotides a negative first order pressure coefficient B 1 was determined indicating an upfield shift of the resonances with pressure. With exception of the α-phosphate group of Mg2+·GMP and Mg2+·GppNHp the second order pressure coefficients are positive. To describe the data of Mg2+·GppCH2p and GTPγS a Taylor expansion of 3rd order is required. For distinguishing pH effects from pressure effects a complete pH titration set is presented for GMP, as well as GDP and GTP in absence and presence of Mg2+ ions using indirect referencing to DSS under identical experimental conditions. By a comparison between high pressure 31P NMR data on free Mg2+-GDP and Mg2+-GDP in complex with the proto-oncogene Ras we demonstrate that pressure induced changes in chemical shift are clearly different between both forms.

Pressure dependence of backbone chemical shifts in the model peptides Ac-Gly-Gly-Xxx-Ala-NH2.

For a better understanding of nuclear magnetic resonance (NMR) detected pressure responses of folded as well as unstructured proteins the availability of data from well-defined model systems are indispensable. In this work we report the pressure dependence of chemical shifts of the backbone atoms (1)H(α), (13)C(α) and (13)C' in the protected tetrapeptides Ac-Gly-Gly-Xxx-Ala-NH2 (Xxx one of the 20 canonical amino acids). Contrary to expectation the chemical shifts of these nuclei have a nonlinear dependence on pressure in the range from 0.1 to 200 MPa. The polynomial pressure coefficients B 1 and B 2 are dependent on the type of amino acid studied. The coefficients of a given nucleus show significant linear correlations suggesting that the NMR observable pressure effects in the different amino acids have at least partly the same physical cause. In line with this observation the magnitude of the second order coefficients of nuclei being direct neighbors in the chemical structure are also weakly correlated.

Self-Assembly of Reactive Linear Cu3 Building Blocks for Supramolecular Coordination Chemistry and Their Reactivity toward E(n) Ligand Complexes.

This study describes the selective synthesis of linear, trinuclear, halide-bridged Cu(I) complexes [Cu3(µ-X)2(µ-dpmp)2(MeCN)2](+) (1a: X = Cl; 1b: X = Br; 1c: X = I) stabilized by the tridentate dpmp ligand obtained by self-assembly reactions in THF/MeCN. Upon drying, the MeCN ligands can be removed and the complexes are transformed to the reactive parent trinuclear [Cu3(µ-X)2(µ-dpmp)2](+) (2a-c) building blocks with two vacant coordination sites on the terminal Cu atoms. Another synthesis in CH2Cl2 directly yields 2a-c. Additionally, two related isomeric compounds, 2a* and 2c*, and two CH2Cl2-ligated complexes, [Cu3(µ-X)2(µ-dpmp)2(CH2Cl2)2](+) (X = Br (3b), I (3c)), were structurally characterized. The frameworks of the cationic [Cu3(µ-X)2(µ-dpmp)2](+) complexes are stable in solution at low temperatures and show dynamic coordination behavior at elevated temperatures, indicated by new signals arising in the (31)P{(1)H} NMR spectra. This evolution cannot be shifted back by decreasing the temperature again. However, cationic [Cu3(µ-X)2(µ-dpmp)2](+) (X = Cl, Br, I) complexes can be obtained selectively in the solid state upon crystallization. Although reactions of 2a-c with complexes [{CpMo(CO)2}2(µ,η(2):η(2)-E2)] (E = P (A1), As (A2)) led to unsymmetrically substituted [Cu3(µ-X)2(µ-dpmp)2(η(1)-L)](+) (4a-c: X = Cl-I, L = A1; 5: X = Cl, L = A2) complexes, reactions with the cyclo-P3 complex [CpMo(CO)2(η(3)-P3)] (B) afforded zigzag chain polymers [Cu3(µ-X)2(µ-dpmp)2(µ,η(1):η(1)-B)]n[BF4]n (6a: X = Cl; 6b: X = Br) and symmetrically substituted complex [Cu3(µ-I)2(µ-dpmp)2(η(1)-B)2](+) (7). Reactions of 2a-c with cyclo-E5 complexes [Cp*Fe(η(5)-E5)] (E = P (C1), As (C2)) led to the isolation of one-dimensional coordination polymers [Cu3(µ-X)2(µ-dpmp)2(µ,η(1):η(1)-L)]n[BF4]n (8a-b: X = Cl-Br, L = C1; 9: X = Cl, L = C2) and symmetrically substituted complex [Cu3(µ-I)2(µ-dpmp)2(η(1)-C1)2](+) (10). All products exhibit a trinuclear, cationic [Cu3(µ-X)2(µ-dpmp)2](+) complex as the central structural motif. Variation of the intramolecular Cu-Cu distances inside the Cu3 complexes is discussed, and supporting DFT computations for the model complex [Cu3(µ-Cl)2(dmmp)2{(η(1)-A1)}](+) (4a') are presented.

The Chemical Shift Baseline for High-Pressure NMR Spectra of Proteins.

High-pressure (HP) NMR spectroscopy is an important method for detecting rare functional states of proteins by analyzing the pressure response of chemical shifts. However, for the analysis of the shifts it is mandatory to understand the origin of the observed pressure dependence. Here we present experimental HP NMR data on the (15) N-enriched peptide bond model, N-methylacetamide (NMA), in water, combined with quantum-chemical computations of the magnetic parameters using a pressure-sensitive solvation model. Theoretical analysis of NMA and the experimentally used internal reference standard 4,4-dimethyl-4-silapentane-1-sulfonic (DSS) reveal that a substantial part of observed shifts can be attributed to purely solvent-induced electronic polarization of the backbone. DSS is only marginally responsive to pressure changes and is therefore a reliable sensor for variations in the local magnetic field caused by pressure-induced changes of the magnetic susceptibility of the solvent.

Giant Rugby Ball [{Cp(Bn)Fe(η(5)-P5)}24Cu96Br96] Derived from Pentaphosphaferrocene and CuBr2.

The self-assembly of [Cp(Bn)Fe(η(5)-P5)] (Cp(Bn) = η(5)-C5(CH2Ph)5) with CuBr2 leads to the formation of an unprecedented rugby ball-shaped supramolecule consisting of 24 units of the pentaphosphaferrocene and an extended CuBr framework, which does not follow the fullerene topology. The resulting scaffold of 312 noncarbon atoms reveals three different coordination modes of the cyclo-P5 ligand including a novel π-coordination. The outer dimensions of 3.7 × 4.6 nm of the sphere approach the range of the size of proteins. With a value of 32.1 nm(3), it is 62 times larger in volume than a C60 molecule. Surprisingly, this giant rugby ball is also slightly soluble in CH2Cl2.

Human cytomegalovirus major immediate early 1 protein targets host chromosomes by docking to the acidic pocket on the nucleosome surface.

The 72-kDa immediate early 1 (IE1) protein encoded by human cytomegalovirus (hCMV) is a nuclearly localized promiscuous regulator of viral and cellular transcription. IE1 has long been known to associate with host mitotic chromatin, yet the mechanisms underlying this interaction have not been specified. In this study, we identify the cellular chromosome receptor for IE1. We demonstrate that the viral protein targets human nucleosomes by directly binding to core histones in a nucleic acid-independent manner. IE1 exhibits two separable histone-interacting regions with differential binding specificities for H2A-H2B and H3-H4. The H2A-H2B binding region was mapped to an evolutionarily conserved 10-amino-acid motif within the chromatin-tethering domain (CTD) of IE1. Results from experimental approaches combined with molecular modeling indicate that the IE1 CTD adopts a ß-hairpin structure, docking with the acidic pocket formed by H2A-H2B on the nucleosome surface. IE1 binds to the acidic pocket in a way similar to that of the latency-associated nuclear antigen (LANA) of the Kaposi's sarcoma-associated herpesvirus. Consequently, the IE1 and LANA CTDs compete for binding to nucleosome cores and chromatin. Our work elucidates in detail how a key viral regulator is anchored to human chromosomes and identifies the nucleosomal acidic pocket as a joint target of proteins from distantly related viruses. Based on the striking similarities between the IE1 and LANA CTDs and the fact that nucleosome targeting by IE1 is dispensable for productive replication even in "clinical" strains of hCMV, we speculate that the two viral proteins may serve analogous functions during latency of their respective viruses.

Genetic associations with lipoprotein subfractions provide information on their biological nature.

Adverse levels of lipoproteins are highly heritable and constitute risk factors for cardiovascular outcomes. Hitherto, genome-wide association studies revealed 95 lipid-associated loci. However, due to the small effect sizes of these associations large sample numbers (>100 000 samples) were needed. Here we show that analyzing more refined lipid phenotypes, namely lipoprotein subfractions, can increase the number of significantly associated loci compared with bulk high-density lipoprotein and low-density lipoprotein analysis in a study with identical sample numbers. Moreover, lipoprotein subfractions provide novel insight into the human lipid metabolism. We measured 15 lipoprotein subfractions (L1-L15) in 1791 samples using (1)H-NMR (nuclear magnetic resonance) spectroscopy. Using cluster analyses, we quantified inter-relationships among lipoprotein subfractions. Additionally, we analyzed associations with subfractions at known lipid loci. We identified five distinct groups of subfractions: one (L1) was only marginally captured by serum lipids and therefore extends our knowledge of lipoprotein biochemistry. During a lipid-tolerance test, L1 lost its special position. In the association analysis, we found that eight loci (LIPC, CETP, PLTP, FADS1-2-3, SORT1, GCKR, APOB, APOA1) were associated with the subfractions, whereas only four loci (CETP, SORT1, GCKR, APOA1) were associated with serum lipids. For LIPC, we observed a 10-fold increase in the variance explained by our regression models. In conclusion, NMR-based fine mapping of lipoprotein subfractions provides novel information on their biological nature and strengthens the associations with genetic loci. Future clinical studies are now needed to investigate their biomedical relevance.

Pressure response of amide one-bond J-couplings in model peptides and proteins.

The pressure dependence of the one-bond indirect spin-spin coupling constants (1)J(N-H) was studied in the protected tetrapeptides Ac-Gly-Gly-Xxx-Ala-NH2 (with Xxx being one of the 20 proteinogenic amino acids). The response of the (1)J(N-H) coupling constants is amino acid type specific, with an average increase of its magnitude by 0.6 Hz at 200 MPa. The variance of the pressure response is rather large, the largest pressure effect is observed for asparagine where the coupling constant becomes more negative by -2.9 Hz at 200 MPa. The size of the J-coupling constant at high pressure is positively correlated with its low pressure value and the ß-propensity, and negatively correlated with the amide proton shift and the first order nitrogen pressure coefficient and the electrostatic solvation free energy.