Cardiac anatomy, function and metabolism in elite cyclists assessed by magnetic resonance imaging and spectroscopy.

We investigated whether left ventricular hypertrophy in elite cyclists is associated with functional changes or abnormal energy metabolism. Left ventricular hypertrophy is a powerful risk factor for sudden cardiac death with different prognostic significance among the various geometric forms. Cyclists may have a combination of mixed eccentric and concentric hypertrophy. Magnetic resonance imaging was used to define left ventricular mass, geometry and function. Thirteen highly trained male cyclists and 12 healthy controls were investigated. Proton-decoupled phosphorus-31 cardiac spectroscopy was performed to assess parameters of myocardial high-energy phosphate metabolism. Left ventricular mass and end-diastolic volumes normalized for body surface area were significantly higher in cyclists (124.1 +/- 9.4 g.m-2 and 106.2 +/- 11.4 ml.m-2, respectively) than in controls (85.9 +/- 9.3 g.m-2 and 79.1 +/- 11.6 ml.m-2, respectively), (both P < 0.0001). The left ventricular mass to end-diastolic volume ratio, as a parameter of left ventricular geometry, was not significantly increased in cyclists compared to controls. Resting left ventricular ejection fraction, cardiac index, and systolic wall stress in cyclists did not differ significantly from those of controls. The phosphocreatine to adenosine triphosphate ratio was not significantly different between cyclists and controls (2.2 +/- 0.34 vs 2.2 +/- 0.17, ns). Cyclists show prominent left ventricular hypertrophy with normal geometry. The finding that the hypertrophic hearts of the cyclists had normal left ventricular function and a normal phosphocreatine to adenosine triphosphate ratio suggests that sport-induced left ventricular hypertrophy is a physiological adaptation rather than a pathophysiological response.

Structure of the complex of lac repressor headpiece and an 11 base-pair half-operator determined by nuclear magnetic resonance spectroscopy and restrained molecular dynamics.

The structure of the complex of lac repressor headpiece and an 11 base-pair lac half-operator has been determined by NMR spectroscopy and restrained Molecular Dynamics calculations. In total 508 distances were derived from two-dimensional nuclear Overhauser enhancement measurements, 260 of which are within the headpiece, 212 within the operator and 36 between operator and headpiece. An equilibrium restrained Molecular Dynamics calculation of the complex in aqueous solution, spanning 85 picoseconds, has been used to analyze the structure. Configuration sampling by an annealing procedure has been undertaken as well in order to estimate the precision of the structure determination. Our data confirm the results of previous two-dimensional NMR studies that the orientation of the recognition helix of lac repressor in the major groove of DNA with respect to the operator dyad axis is opposite to the orientation found in complexes of other DNA binding proteins of the helix-turn-helix class. We find a number of tight contacts between the protein and the operator that are in agreement with the available genetic and biochemical data. The anchoring of lac headpiece on the operator is similar to that of other repressors. Other features are unique for lac headpiece: relative few direct hydrogen bonds between side-chains and bases; extensive apolar contacts; many direct and water-bridged contacts to phosphates from residues in or close to the recognition helix. Overall, an interconnected set of interactions is observed, involving base-specific contacts, phosphate contacts, intra-protein and water-bridged hydrogen bonds. Several of these interactions appear to be dynamic, i.e. fluctuating in time, rather than static.

"Ensemble" iterative relaxation matrix approach: a new NMR refinement protocol applied to the solution structure of crambin.

The structure in solution of crambin, a small protein of 46 residues, has been determined from 2D NMR data using an iterative relaxation matrix approach (IRMA) together with distance geometry, distance bound driven dynamics, molecular dynamics, and energy minimization. A new protocol based on an "ensemble" approach is proposed and compared to the more standard initial rate analysis approach and a "single structure" relaxation matrix approach. The effects of fast local motions are included and R-factor calculations are performed on NOE build-ups to describe the quality of agreement between theory and experiment. A new method for stereospecific assignment of prochiral groups, based on a comparison of theoretical and experimental NOE intensities, has been applied. The solution structure of crambin could be determined with a precision (rmsd from the average structure) of 0.7 A on backbone atoms and 1.1 A on all heavy atoms and is largely similar to the crystal structure with a small difference observed in the position of the side chain of Tyr-29 which is determined in solution by both J-coupling and NOE data. Regions of higher structural variability (suggesting higher mobility) are found in the solution structure, in particular for the loop between the two helices (Gly-20 to Pro-22).

Assignment of the 1H-NMR spectrum of a lac repressor headpiece-operator complex in H2O and identification of NOEs. Consequences for protein-DNA interaction.

A complex between the headpiece amino-terminal residues 1-56 of lac repressor (HP56) and an 11-bp lac operator fragment was studied by 1H NMR. The sequence specific assignment of the exchangeable and non-exchangeable protons has been accomplished. Several protons have favourable chemical shifts in the complex, therefore new intraprotein NOEs could be found that had not been unambigously identified in the free protein. By comparison, most of these intraprotein NOEs are also present in the spectra of the free headpiece but some are different. Furthermore, several new proteins DNA NOEs could be identified. The NOE between the side-chain amide protons of Gln18 and C5H of C7 confirms the specific contact between these residues which was proposed from genetic experiments [Ebright, R. M. (1985) J. Biomol. Struct. & Dyn. 3, 281-297]. The implications of the new data for the interaction between the lac repressor headpiece and its operator are discussed.

Genetic analysis of the LexA repressor: isolation and characterization of LexA(Def) mutant proteins.

We report the isolation of LexA mutant proteins with impaired repressor function. These mutant proteins were obtained by transforming a LexA-deficient recA-lacZ indicator strain with a randomly mutagenized plasmid harbouring the lexA gene and subsequent selection on MacConkey-lactose indicator plates. A total of 24 different lexA(Def) missense mutations were identified. All except three mutant proteins are produced in near-normal amounts suggesting that they are fairly resistant to intracellular proteases. All lexA(Def) missense mutations are situated within the first 67 amino acids of the amino-terminal DNA binding domain. The properties of an intragenic deletion mutant suggest that the part of the amino-terminal domain important for DNA recognition or domain folding should extent at least to amino acids 69 or 70. A recent 2D-NMR study (Lamerichs et al. 1989) has identified three alpha helices in the DNA binding domain of LexA. The relative orientation of two of them (helices 2 and 3) is reminiscent of, but not identical to, the canonical helix-turn-helix motif suggesting nevertheless that helix 3 might be involved in DNA recognition. The distribution of the lexA(Def) missense mutations along the first 67 amino-terminal amino acids indeed shows some clustering within helix 3, since 8 out of the 24 different missense mutations are found in this helix. However one mutation in front of helix 1 and five mutations between amino acids 61 and 67 suggest that elements other than helices 2 and 3 may be important for DNA binding.

Two-dimensional NMR study of a protein-DNA complex. lac repressor headpiece-operator interaction.

The interaction of the N-terminal DNA-binding domain (56 amino acid residues) of the lac repressor with lac operator DNA was analyzed using two-dimensional NMR spectroscopy. Both half-operators (11 and 14 bp) and a complete fully symmetric 22 bp operator were studied. Two-dimensional nuclear Overhauser effect (2D NOE) spectra of headpiece-operator complexes were taken in both D2O and H2O solutions. Special attention was given to the problem of 1H resonance assignments. Based on an analysis of the proton-proton NOEs, a model for the headpiece-operator complex could be derived. In this model, most of the protein-DNA contracts occur between amino acid residues in the second helix (recognition helix) of the lac headpiece and DNA bases in the major groove. The orientation of this helix with respect to the dyad axis of the operator is opposite to that found in the X-ray structures of several other repressor-operator complexes.

The amino-terminal domain of LexA repressor is alpha-helical but differs from canonical helix-turn-helix proteins: a two-dimensional 1H NMR study.

The amino-terminal DNA binding domain of LexA repressor consisting of 84 amino acid residues has been studied by two-dimensional 1H NMR. Sequence-specific 1H resonance assignments were made for the first 60 amino acid residues. The secondary structure of this part of the protein contains three alpha-helices in the peptide segments 8-20, 28-35, and 41-54. The last helix has a distortion around residues 47-48. The peptide segment 28-47 shows weak homology with other helix-turn-helix proteins. To investigate the spatial structure of this region of the molecule distance-geometry calculations were performed based on proton-proton distance constraints from nuclear Overhauser effects. The resulting structure shows that the segment 28-47 contains two helices with a loop region between them. The relative orientation of the two helices is similar to that found in helix-turn-helix proteins, but the helices are further apart, with the phenyl ring of Phe-37 located between them. The Brookhaven Protein Data Bank was searched for structurally homologous peptide segments in other proteins. The result of this search was that the two-helical structure of LexA is not more closely related to the canonical helix-turn-helix motif than it is to similar substructures found in other classes of proteins.

H NMR study of a complex between the lac repressor headpiece and a 22 base pair symmetric lac operator.

A complex between the lac repressor headpiece and a fully symmetric tight-binding 22 bp lac operator was studied by 2D NMR. Several 2D NOE spectra were recorded for the complex in both H2O and 2H2O. Many NOE cross-peaks between the headpiece and DNA could be identified, and changes in the chemical shift of the DNA protons upon complex formation were analyzed. Comparison of these data with those obtained for a complex between the headpiece and a 14 bp half-operator, studied previously [Boelens, R., Scheek, R. M., Lamerichs, R. M. J. N., de Vlieg, J., van Boom, J. H., & Kaptein, R. (1987) in DNA-ligand interactions (Guschlbauer, W., & Saenger, W., Eds.) pp 191-215, Plenum, New York], shows that two headpieces form a specific complex with the 22 bp lac operator in which each headpiece binds in the same way as found for the 14 bp complex. The orientation of the recognition helix in the major groove of DNA in these complexes is opposite with respect to the dyad axis to that found for other repressors.

The interaction of lac repressor headpiece with its operator: an NMR view.

Analysis of nuclear Overhauser enhancements in two-dimensional NMR spectra of the complex of lac repressor headpiece with a 14 base pair lac operator fragment shows that the second helix of the headpiece binds in the major groove of DNA, as has been suggested. The orientation of this helix is approximately 180 degrees different from the proposed models and from that found in the X-ray structure of the 434 repressor-operator complex. The model of the lac headpiece-operator complex provides a good explanation for a large amount of biochemical, genetic and physical data.

Secondary structure and hydrogen bonding of crambin in solution. A two-dimensional NMR study.

The secondary structure of crambin in solution has been determined using two-dimensional NMR and is found to be essentially identical to that of the crystal structure. The H-D exchange of most amide protons can be accounted for in terms of the hydrogen bonds found in the X-ray structure. Exceptions are the amide protons of Cys-4 and Ser-6, which exchange more slowly than expected, and of Asn-46 for which the exchange is faster. These results might be explained by a slightly different conformation of the C-terminal region of the protein in solution. The slow exchange of the amides of Cys-32 and Glu-23 might be due to aggregation involving an extremely hydrophobic part of the protein in solution.