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Biomedical subjects

M S Weiss

Publications and source records attributed to M S Weiss.

At least 19 recordsLinked to original sources
PubMed2006

The structure of the hexagonal crystal form of hen egg-white lysozyme.

The three-dimensional structure of hen egg-white lysozyme (HEWL) in a hexagonal crystal form has been determined and refined to 1.46 A resolution. This hexagonal crystal form crystallizes from a saturated sodium nitrate solution at pH 8.4. The crystals belong to space group P6(1)22, with unit-cell parameters a = b = 85.64, c = 67.93 A. A total of 165 water molecules, 16 nitrate ions and five sodium ions were located in the electron-density map. The hexagonal crystal form exhibits a higher solvent content and a higher degree of disorder than other crystal forms of lysozyme. The flexibility of the protein depends on the crystal packing, although some residue ranges are flexible in all native HEWL crystal forms.

Animals↗
PubMed2001

On the routine use of soft X-rays in macromolecular crystallography.

A diffraction data set has been collected from a blood coagulation factor XIII-Ca(2+) complex crystal at the X-ray diffraction beamline of the ELETTRA synchrotron (Trieste, Italy) at a wavelength of 2.6 A. The data collection could be carried out using the beamline as is, without making any time-consuming changes to the apparatus. Various data-processing schemes have been employed and it has been observed that local or detector scaling procedures are essential for producing the 'best' anomalous differences.

Crystallography, X-Ray↗
PubMed2001

C-H...pi-interactions in proteins.

A non-redundant set of 1154 protein structures from the Protein Data Bank was examined with respect to close interactions between C-H-donor and pi-acceptor groups. A total of 31,087 interactions were found to satisfy our selection criteria. Their geometric parameters suggest that these interactions can be classified as weak hydrogen bonds.A set of 12 interaction classes were defined based on the division of the donors into three groups and the acceptors into four groups. These classes were examined separately, and the respective interactions described in detail in each class. Most prominent were interactions between aliphatic C-H donors and aromatic pi-acceptors and interactions between aromatic C-H donors and aromatic pi-acceptors. About three-quarters of the Trp-rings, half of all Phe and Tyr-rings and a quarter of all His-rings were found to be involved as acceptors in C-H...pi-interactions. On the donor side, a preference for aromatic C-H groups was observed, but also for the aliphatic side-chains of the long, extended amino acid residues Lys, Arg and Met, and the Pro ring. The average distance between the C-donor and the center-of-mass of the pi-acceptor was observed to be significantly longer in the 174 protein structures determined at >2.5 A resolution. Also, the distribution is significantly wider. This resolution dependence suggests that the force fields commonly used for the refinement of protein structures may not be adequate. C-H...pi-interactions involving aromatic groups either as donor or as acceptor groups are found mostly in the interior of the protein. The more hydrophilic the participating groups are, the closer to the surface are the interactions located. About 40 % of all C-H...pi-interactions occur between amino acid residue side-chains that are separated by nine or less residues in sequence. Dependent on the interaction class, different preferences for secondary structure, residue type and side-chain conformation were observed. It is likely that the C-H...pi-interactions contribute significantly to the overall stability of a protein.

Databases, Factual↗
PubMed2001

More hydrogen bonds for the (structural) biologist.

Why does a given protein structure form and why is this structure stable? These fundamental biochemical questions remain fascinating and challenging problems because the physical bases of the forces that govern protein structure, stability and folding are still not well understood. Now, a general concept of hydrogen bonding in proteins is emerging. This concept involves not only N-H and O-H donor groups, but also C-H, and not only N and O as acceptor groups, but also pi-systems. We postulate that the incorporation of the entirety of these interactions leads to a more complete description of the problem, and that this could provide new perspectives and possibly new answers.

Carrier Proteins↗
PubMed2001

Crystal structure of Mip, a prolylisomerase from Legionella pneumophila.

The human pathogen Legionella pneumophila, the etiological agent of the severe and often fatal Legionnaires' disease, produces a major virulence factor, termed 'macrophage infectivity potentiator protein' (Mip), that is necessary for optimal multiplication of the bacteria within human alveolar macrophages. Mip exhibits a peptidyl prolyl cis-trans isomerase (PPIase) activity, which appears to be important for infection. Here we report the 2.4 A crystal structure of the Mip protein from L. pneumophila Philadelphia 1 and the 3.2 A crystal structure of its complex with the drug FK506. Each monomer of the homodimeric protein consists of an N-terminal dimerization module, a long (65 A) connecting alpha-helix and a C-terminal PPIase domain exhibiting similarity to human FK506-binding protein. In view of the recent significant increase in the number of reported cases of Legionnaires' disease and other intracellular infections, these structural results are of prime interest for the design of new drugs directed against Mip proteins of intracellular pathogens.

Anti-Bacterial Agents↗
PubMed2001

Calcium binding of transglutaminases: a 43Ca NMR study combined with surface polarity analysis.

Transglutaminases (TGases) form cross-links between glutamine and lysine side-chains of polypeptides in a Ca2+-dependent reaction. The structural basis of the Ca2+-effect is poorly defined. 43Ca NMR, surface polarity analysis combined with multiple sequence alignment and the construction of a new homology model of human tissue transglutaminase (tTGase) were used to obtain structural information about Ca2+ binding properties of factor XIII-A2, tTGase and TGase 3 (each of human origin). 43Ca NMR provided higher average dissociation constants titrating on a wide Ca2+-concentration scale than previous studies with equilibrium dialysis performed in shorter ranges. These results suggest the existence of low affinity Ca2+ binding sites on both FXIII-A and tTGase in addition to high affinity ones in accordance with our surface polarity analysis identifying high numbers of negatively charged clusters. Upon increasing the salt concentration or activating with thrombin, FXIII-A2 partially lost its original Ca2+ affinity; the NMR data suggested different mechanisms for the two activation processes. The NMR provided structural evidence of GTP-induced conformational changes on the tTGase molecule diminishing all of its Ca2+ binding sites. NMR data on the Ca2+ binding properties of the TGase 3 are presented here; it binds Ca2+ the most tightly, which is weakened after its proteolytic activation. The investigated TGases seem to have very symmetric Ca2+ binding sites and no EF-hand motifs.

Amino Acid Sequence↗
PubMed2001

Vagal cardiac function and arterial blood pressure stability.

This study was designed to investigate the importance of vagal cardiac modulation in arterial blood pressure (ABP) stability before and after glycopyrrolate or atropine treatment. Changes in R-R interval (RRI) and ABP were assessed in 10 healthy young (age, 22 +/- 1.8 yr) volunteers during graded lower body negative pressure (LBNP) before and after muscarinic cholinergic (MC) blockade. Transient hypertension was induced by phenylephrine (1 microg/kg body wt), whereas systemic hypotension was induced by bilateral thigh cuff deflation after a 3-min suprasystolic occlusion. Power spectral densities of systolic [systolic blood pressure (SBP)] and diastolic ABP variability were examined. Both antimuscarinic agents elicited tachycardia similarly without significantly affecting baseline ABP. The increase in SBP after phenylephrine injection (+14 +/- 2 mmHg) was significantly augmented with atropine (+26 +/- 2 mmHg) or glycopyrrolate (+27 +/- 3 mmHg) and associated with a diminished reflex bradycardia. The decrease in SBP after cuff deflation (-9.2 +/- 1.2 mmHg) was significantly greater after atropine (-15 +/- 1 mmHg) or glycopyrrolate (-14 +/- 1 mmHg), with abolished reflex tachycardia. LBNP significantly decreased both SBP and RRI. However, after antimuscarinic agents, the reduction in SBP was greater (P < 0.05) and was associated with less tachycardia. Antimuscarinic agents reduced (P < 0.05) the low-frequency (LF; 0.04-0.12 Hz) power of ABP variability at rest. The LF SBP oscillation was significantly augmented during LBNP, which was accentuated (P < 0.05) after antimuscarinic agents and was correlated (r = -0.79) with the decrease in SBP. We conclude that antimuscarinic agents compromised ABP stability by diminishing baroreflex sensitivity, reflecting the importance of vagal cardiac function in hemodynamic homeostasis. The difference between atropine and glycopyrrolate was not significant.

Adrenergic alpha-Agonists↗
PubMed2000

Crystallization, structure solution and refinement of hen egg-white lysozyme at pH 8.0 in the presence of MPD.

Hen egg-white lysozyme has been crystallized at slightly alkaline pH using 2-methyl-2,4-pentanediol (MPD) as the precipitant. The crystals are nearly isomorphous to crystals grown at acidic pH using sodium chloride as the precipitant. However, the growth kinetics differ markedly between the two conditions. The major reason for this is a molecule of MPD that binds tightly in between two lysozyme molecules and favors the growth of the crystals along the crystallographic c direction over growth perpendicular to it.

Animals↗
PubMed2000

Orthostatic hypotension in aging humans.

We tested the hypothesis that hypotension occurred in older adults at the onset of orthostatic challenge as a result of vagal dysfunction. Responses of heart rate (HR) and mean arterial pressure (MAP) were compared between 10 healthy older and younger adults during onset and sustained lower body negative pressure (LBNP). A younger group was also assessed after blockade of the parasympathetic nervous system with the use of atropine or glycopyrrolate and after blockade of the beta(1)-adrenoceptor by use of metoprolol. Baseline HR (older vs. younger: 59 +/- 4 vs. 54 +/- 1 beats/min) and MAP (83 +/- 2 vs. 89 +/- 3 mmHg) were not significantly different between the groups. During -40 Torr, significant tachycardia occurred at the first HR response in the younger subjects without hypotension, whereas significant hypotension [change in MAP (DeltaMAP) -7 +/- 2 mmHg] was observed in the elderly without tachycardia. After the parasympathetic blockade, tachycardiac responses of younger subjects were diminished and associated with a significant hypotension at the onset of LBNP. However, MAP was not affected after the cardiac sympathetic blockade. We concluded that the elderly experienced orthostatic hypotension at the onset of orthostatic challenge because of a diminished HR response. However, an augmented vasoconstriction helped with the maintenance of their blood pressure during sustained LBNP.

Adrenergic beta-Antagonists↗
PubMed1999

A method to detect nonproline cis peptide bonds in proteins.

Based on the geometrical parameters around seventeen incorrectly assigned trans conformations of peptide bonds in protein structures and their correct cis counterparts, we have devised an algorithm that is capable of detecting these sites. The algorithm was optimized to reliably find all of the seventeen test cases. It can be used to quickly scan an atomic coordinate file or the complete Brookhaven Protein Data Base for more likely candidates for non-Pro cis peptide bonds. Also, it can be of help to guide the crystallographer in intermediate stages of structure determination towards suspect areas.

Algorithms↗
PubMed1999

A structure-based mechanism for copper-zinc superoxide dismutase.

A reaction cycle is proposed for the mechanism of copper-zinc superoxide dismutase (CuZnSOD) that involves inner sphere electron transfer from superoxide to Cu(II) in one portion of the cycle and outer sphere electron transfer from Cu(I) to superoxide in the other portion of the cycle. This mechanism is based on three yeast CuZnSOD structures determined by X-ray crystallography together with many other observations. The new structures reported here are (1) wild type under 15 atm of oxygen pressure, (2) wild type in the presence of azide, and (3) the His48Cys mutant. Final R-values for the three structures are respectively 20.0%, 17.3%, and 20.9%. Comparison of these three new structures to the wild-type yeast Cu(I)ZnSOD model, which has a broken imidazolate bridge, reveals the following: (i) The protein backbones (the "SOD rack") remain essentially unchanged. (ii) A pressure of 15 atm of oxygen causes a displacement of the copper ion 0.37 A from its Cu(I) position in the trigonal plane formed by His46, His48, and His120. The displacement is perpendicular to this plane and toward the NE2 atom of His63 and is accompanied by elongated copper electron density in the direction of the displacement suggestive of two copper positions in the crystal. The copper geometry remains three coordinate, but the His48-Cu bond distance increases by 0.18 A. (iii) Azide binding also causes a displacement of the copper toward His63 such that it moves 1.28 A from the wild-type Cu(I) position, but unlike the effect of 15 atm of oxygen, there is no two-state character. The geometry becomes five-coordinate square pyramidal, and the His63 imidazolate bridge re-forms. The His48-Cu distance increases by 0.70 A, suggesting that His48 becomes an axial ligand. (iv) The His63 imidazole ring tilts upon 15 atm of oxygen treatment and azide binding. Its NE2 atom moves toward the trigonal plane by 0.28 and 0.66 A, respectively, in these structures. (v) The replacement of His48 by Cys, which does not bind copper, results in a five-coordinate square pyramidal, bridge-intact copper geometry with a novel chloride ligand. Combining results from these and other CuZnSOD crystal structures, we offer the outlines of a structure-based cyclic mechanism.

Amino Acid Substitution↗
PubMed1999

Non-proline cis peptide bonds in proteins.

In a non-redundant set of 571 proteins from the Brookhaven Protein Data Base, a total of 43 non-proline cis peptide bonds were identified. Average geometrical parameters of the well-defined cis peptide bonds in proteins determined at high resolution show that some parameters, most notably the bond angle at the amide bond nitrogen, deviate significantly from the corresponding one in the trans conformation. Since the same feature was observed in cis amide bonds in small molecule structures found in the Cambridge Structural Data Base, a new set of parameters for the refinement of protein structures containing non-Pro cis peptide bonds is proposed.A striking preference was observed for main-chain dihedral angles of the residues involved in cis peptide bonds. All residues N-terminal and most residues C-terminal to a non-Pro cis peptide bond (except Gly) are located in the beta-region of a phi/psi plot. Also, all of the few C-terminal residues (except Gly) located in the alpha-region of the phi/psi plot constitute the start of an alpha-helix in the respective structure. In the majority of cases, an intimate side-chain/side-chain interaction was observed between the flanking residues, often involving aromatic side-chains. Interestingly, most of the cases found occur in functionally important regions such as close to the active site of proteins. It is intriguing that many of the proteins containing non-proline cis peptide bonds are carbohydrate-binding or processing proteins. The occurrence of these unusual peptide bonds is significantly more frequent in structures determined at high resolution than in structures determined at medium and low resolution, suggesting that these bonds may be more abundant than previously thought. On the basis of our experience with the structure determination of coagulation factor XIII, we developed an algorithm for the identification of possibly overlooked cis peptide bonds that exploits the deviations of geometrical parameters from ideality. A few likely candidates based on our algorithm have been identified and are discussed.

Algorithms↗
PubMed1999

Dehydration leads to a phase transition in monoclinic factor XIII crystals.

Monoclinic factor XIII crystals have been transferred to a solution containing increasing amounts of the precipitant PEG 6000. At a concentration of about 36%(w/v) PEG 6000, a phase transition was observed. The space group of the crystals was preserved on the transition, but half of the 2(1) screw axes were lost, which meant that the unit-cell volume and the content of the asymmetric unit were doubled. The structure of factor XIII in the new crystal form was solved by molecular replacement. About 80% of the changes accompanying the transition can be explained by a rigid-body rotation of half of the factor XIII dimers in the lattice by about 5 degrees. The remaining changes are mostly small interdomain movements of the four domains which constitute one factor XIII monomer.

Crystallization↗
PubMed1998

Two non-proline cis peptide bonds may be important for factor XIII function.

The structure of recombinant human cellular factor XIII zymogen was solved in its monoclinic crystal form and refined to an R-factor of 18.3% (Rfree = 23.6%) for all data between 40.0 and 2.1 A resolution. Two non-proline cis peptide bonds were detected. One is between Arg310 and Tyr311 close to the active site cysteine residue (Cys314) and the other is between Gln425 and Phe426 at the dimerization interface. The structure and the role of these cis peptides are discussed in the light of their possible importance for factor XIII function.

Amino Acid Sequence↗
PubMed1998

How to ensure supplier quality from your supplier management program.

Companies are currently abandoning vertical integration in order to focus on their core competencies and capabilities. As a result, higher percentages of their products are being provided by suppliers. In today's global marketplace, customers can demand and receive products that possess excellent quality. In order to remain competitive, companies must be able to provide high-quality products at low prices. The quality of components purchased from suppliers influences product quality more than any other factor except design quality, and since purchased materiel make up such a large percentage of a company's product, ensuring supplier quality has become an economic imperative.

Contract Services↗
PubMed1998

Kinematic response of the neck to voluntary and involuntary flexion.

METHODS: The dynamic head-neck responses of human subjects and cadavers undergoing involuntary impact loading conditions have been studied extensively in order to define the kinematics of the neck undergoing rapid movements, but little detailed information is available regarding slower, voluntary motions. In this study, the dynamic kinematics of head/neck complex during subject-controlled, or voluntary head motion have been investigated to compare with the kinematics to involuntary response. Five male human subjects experienced two-types of posterior/anterior neck flexion: flexion initiated under their own volition, and flexion in response to -15Gx acceleration of the torso. Tri-axial photo target mounts were placed on a custom-fit plate at the mouth, on the first thoracic vertebra, and on the sled. High speed movie cameras captured the photo target motion. Linear and angular displacement and velocity of the head and T1 and sled were computed using customized data-processing software. The neck kinematics were represented by a 2-pin linkage which connected the anatomical origins of the head and T1. RESULTS: The results show that maximum neck flexion relative to the torso was not significantly different between the voluntary and involuntary head motions, but that the head motion was significantly greater during the involuntary sled maneuvers. Maximum flexion velocities of 450 and 1236 degrees x s(-1) were sustained during the voluntary and involuntary maneuvers, respectively. CONCLUSION: These findings are important in understanding the kinematics of the human head/neck complex undergoing rapid and slow movements, and will be valuable in future studies determining a realistic physiological performance corridor for the human neck.

Acceleration↗