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PubMed1997

Coiled-coil structure of group A streptococcal M proteins. Different temperature stability of class A and C proteins by hydrophobic-nonhydrophobic amino acid substitutions at heptad positions a and d.

M proteins and M-like proteins, expressed on the surface of group A streptococci and binding to human plasma proteins, can be divided into two classes, A and C, depending on the structure of the central repeated regions. The class C proteins have been shown to be dimers with a coiled-coil structure. In this work, we have compared the structure and binding of a class A protein, Mrp4, and a class C protein, Arp4, expressed by the same bacterial strain. Circular dichroism spectra, gel filtration, and binding assays showed that both proteins had a coiled-coil dimer configuration and a high-affinity binding at 20 degrees C. However, striking differences were seen at 37 degrees C. The class A protein, Mrp4, was still a coiled-coil dimer with high affinity binding activity, whereas the class C protein, Arp4, had lost both the coiled-coil structure and binding activity. Raising the temperature even higher, Mrp4 retained the coiled-coil structure up to 70-90 degrees C. Furthermore, a recombinant protein, Mrp(C), in which the A-repeats of Mrp4 were replaced by the C-repeats of Arp4, lost its coiled-coil structure and fibrinogen-binding around 40-45 degrees C. These results suggest a high thermal stability of class A proteins and a low stability of class C proteins and that the structural basis for this can be found partly in the A- and C-repeats. Analysis of the amino acid sequences of the A- and C-repeats, revealed a large difference, 87% and 45%, respectively, in the content of hydrophobic amino acid residues in the positions regarded as important for the formation of the coiled-coil structure. In particular, several alanine residues in the A-repeats were replaced by serine residues in the C-repeats. Our results suggest that important structural and functional changes within the M protein family have evolved by specific hydrophobic-nonhydrophobic amino acid replacements.

Amino Acid Sequence↗
PubMed1976

Freezing of actin. Reversible oxidation of a sulfhydryl group and structural change.

It was found that the essential change in actin (whether G- or F-actin) on freeze-thawing was the specific oxidation of one of five sulfhydryl (SH) groups, i.e. the SH group of Cys 373 in the amino acid sequence. Oxidized SH groups formed an inter-molecular disulfide (SS) bond to yield an actin dimer. F-actin, subjected to freeze-thawing (or F-actin obtained by the transformation of once frozen G-actin which is essentially a dimer), has anomalous physico-chemical properties and a different conformation from normal F-actin, as determined by optical and electron microscopic observations, as well as high steady ATP-splitting activity in the presence of Mg2+. However, it was found that those peculiarities disappeared and normal actin was reformed on reducing the oxidized SH group with dithiothreitol (DTT). It was also found that the normal characteristics of actin were preserved for more than four months on freezing in the presence of a sufficient amount of DTT.

Actins↗
PubMed1993

Conformational influence of the ribose 2'-hydroxyl group: crystal structures of DNA-RNA chimeric duplexes.

We have crystallized three double-helical DNA-RNA chimeric duplexes and determined their structures by X-ray crystallography at resolutions between 2 and 2.25 A. The two self-complementary duplexes [r(G)d(CGTATACGC)]2 and [d(GCGT)r(A)d(TACGC)]2, as well as the Okazaki fragment d(GGGTATACGC).r(GCG)d(TATACCC), were found to adopt A-type conformations. The crystal structures are non-isomorphous, and the crystallographic environments for the three chimeras are different. A number of intramolecular interactions of the ribose 2'-hydroxyl groups contribute to the stabilization of the A-conformation. Hydrogen bonds between 2'-hydroxyls and 5'-oxygens or phosphate oxygens, in addition to the previously observed hydrogen bonds to 1'-oxygens of adjacent riboses and deoxyriboses, are observed in the DNA-RNA chimeric duplexes. The crystalline chimeric duplexes do not show a transition between the DNA A- and B-conformations. CD spectra suggest that the Okazaki fragment assumes an A-conformation in solution as well. In this molecule the three RNA residues may therefore lock the complete decamer in the A-conformation. Crystals of an all-DNA strand with the same sequence as the self-complementary chimeras show a morphology which is different from those of the chimera crystals. Moreover, the oligonucleotide does not match any of the sequence characteristics of DNAs usually adopting the A-conformation in the crystalline state (e.g., octamers with short alternating stretches of purines and pyrimidines). In DNA-RNA chimeric duplexes, it is therefore possible that a single RNA residue can drive the conformational equilibrium toward the A-conformation.

Base Sequence↗
PubMed1995

Planning for the future: moving to the multispecialty group organizational structure.

Physicians in a Southeastern community were finding themselves ill equipped to deal with many of the requirements of insurance companies, state governments and managed care organizations. One medical practice was considering moving toward becoming a multispecialty group and adding physicians to keep with their objective of having a "growing practice." This case study is centered around the efforts of the physicians' involvement in the strategic planning process of growing their practice.

Delivery of Health Care↗
PubMed2006

A semi-stochastic model for Salmonella infection in a multi-group herd.

A multi-group semi-stochastic model is formulated to identify possible causes of why different strains of Salmonella develop so much variation in their infection dynamics in UK dairy herds. The model includes demography (managed populations) and various types of transmission: direct, pseudovertical and indirect (via free-living infectious units in the environment). The effects of herd size and epidemiological parameters on mean prevalence of infection and mean time until fade out are investigated. Numerical simulation shows that higher pathogen-induced mortality, shorter infectious period, more persistent immune response and more rapid removal of faeces result in a lower mean prevalence of infection, a shorter mean time until fade out, and a greater probability of fade out of infection within 600 days. Combining these results and those for the deterministic counterpart could explain differences in observed epidemiological patterns and help to identify the factors inducing the decline in reported cases of epidemic strains such as DT104 in cattle. We further investigate the effect of group structure on the probability of a major outbreak by using the stochastic threshold theory in homogeneous populations and that in heterogeneous populations. Numerical studies suggest that group structure makes major outbreaks less likely than would be the case in a homogeneous population with the same basic reproduction number. Moreover, some control strategies are suggested by investigating the effect of epidemiological parameters on the probability of an epidemic.

Animals↗
PubMed1998

Pyrithione biocide interactions with bacterial phospholipid head groups.

Sodium pyrithione and zinc pyrithione (NaPT and ZnPT, respectively) are antimicrobial agents widely used in both the cosmetics and fuel industries. They are also utilized in the mining industry because of their metal chelating properties. They have been shown to depolarize membrane electropotential in fungi and are also known to inhibit fungal and bacterial substrate transport processes. Recent work has shown that both pyrithiones cause the leakage of intracellular material (potassium ions and O.D.260 nm absorbing material) from exposed bacterial cells. The work here reports studies on the interactions between the pyrithiones and the bacterial phospholipid head group structures, at both a practical and a theoretical level, utilizing tube dilution neutralizer studies, scanning spectrophotometry and molecular modelling. The tube dilution neutralizer studies exhibited a decrease in minimum inhibitory concentration (MIC) for both pyrithiones in the presence of extracellular phosphatidyl-ethanolamine and EDTA. Scanning spectrophotometry exhibited the chelation of the central zinc atom from the ZnPT chelate by the addition of EDTA. Molecular modelling studies exhibited the chelation of the phosphatidyl-ethanolamine head group by ZnPT. Zinc pyrithione also exhibited an interaction with the ammonium tail of the head group structures. Sodium pyrithione exhibited electrostatic interactions with the phospholipid head groups in the molecular modelling studies.

Antifungal Agents↗
PubMed1999

Theoretical Study of the Electronic Structure of Group 6 [M(CO)(5)X](-) Species (X = NH(2), OH, Halide, H, CH(3)) and a Reinvestigation of the Role of pi-Donation in CO Lability.

Density functional calculations have been employed to investigate the electronic structure of [M(CO)(5)X](-) species (M = Cr, Mo, W; X = NH(2), OH, halide, H, CH(3)) and to compute CO ligand dissociation energies. The calculations indicate that CO loss is most facile from the cis position, and CO dissociation energies are computed to increase along the series X = NH(2) < OH < F < Cl < Br < I < CH(3) < H. These results are in agreement with available experimental data. Trends in CO dissociation are related to the ability of X to stabilize the unsaturated 16e [M(CO)(4)X](-) species formed. In addition, pi-destabilization of the ground-state [M(CO)(5)X](-) species is equally significant. Analysis of the electronic structure of the 18e species shows that Xpi-dpi 4e destabilization results in hybridization at the metal center which enhances trans M-CO but reduces cis M-CO pi-back-donation. Strong pi-donation from X also induces sigma-antibonding interactions between the metal and the cis CO ligands. A fragment analysis reveals that these effects are strongest for the "hard" fluoride, hydroxide, and amide ligands.

Journal Article↗
PubMed2005

Infrared spectra and structures for group 4 dihydroxide and tetrahydroxide molecules.

Hafnium and zirconium atoms react with H(2)O(2) molecules and with H(2) + O(2) mixtures to form M(OH)(2) and M(OH)(4) molecules, which are trapped in solid argon and identified from isotopic shifts in the infrared spectra. Electronic structure calculations at the MP2 level converge to almost linear M(OH)(2) and tetrahedral M(OH)(4) molecules and predict vibrational frequencies for mixed isotopic molecules of lower symmetry that are in excellent agreement with experimental measurements, thus substantiating the identification of hafnium and zirconium dihydroxide and tetrahydroxide molecules. Titanium atoms react to give the same product molecules, but Ti(OH)(4) has an S(4) structure with bent Ti-O-H bonds, Ti(OH)(2) appears to be nearly linear, and the more stable tetravalent HM(O)OH isomer is more prominent for Ti. The Group 4 tetrahydroxides reported here are the first examples of pure metal tetrahydroxide molecules.

Journal Article↗
PubMed1989

Differences between multiple personality disorder and other diagnostic groups on structured interview.

The Dissociative Disorders Interview Schedule was administered to 20 subjects with multiple personality disorder, 20 with schizophrenia, 20 with panic disorder, and 20 with eating disorders. The findings showed that multiple personality can be differentiated from the other groups on variables such as history of physical abuse, sexual abuse, substance abuse, sleepwalking, childhood imaginary playmates, secondary features of multiple personality and extrasensory and supernatural experiences. Those with multiple personality also differ from the other groups on DSM-III criteria for multiple personality, psychogenic amnesia, and psychogenic fugue. The groups did not differ on the number of subjects who had had a major depressive episode.

Adult↗
PubMed2006

Crystal structure of group A streptococcus Mac-1: insight into dimer-mediated specificity for recognition of human IgG.

Group A Streptococcus secretes cysteine proteases named Mac-1 and Mac-2 that mediate host immune evasion by targeting both IgG and Fc receptors. Here, we report the crystal structures of Mac-1 and its catalytically inactive C94A mutant in two different crystal forms. Despite the lack of sequence homology, Mac-1 adopts the canonical papain fold. Alanine mutations at the active site confirmed the critical residues involved in a papain-like catalytic mechanism. Mac-1 forms a symmetric dimer in both crystal forms and displays the unique dimer interface among papain superfamily members. Mutations at the dimer interface resulted in a significant reduction in IgG binding and catalysis, suggesting that the dimer contributes to both IgG specificity and enzyme cooperativity. A tunnel observed at the dimer interface constitutes a target for designing potential Mac-1-specific antimicrobial agents. The structures also offer insight into the functional difference between Mac-1 and Mac-2.

Amino Acid Sequence↗
PubMed1995

A1 catecholamine cell group: fine structure and synaptic input from the nucleus of the solitary tract.

Preembedding immunoperoxidase staining methods were used to characterize tyrosine hydroxylase-immunoreactive (TH-ir) elements in the caudal ventrolateral medulla, and to determine the extent to which neurons of the A1 cell group are directly innervated by projections of the nucleus of the solitary tract (NTS). TH-ir neurons in the A1 region were medium-sized and multipolar. They possessed rounded nuclei with infrequent invaginations, well-developed Golgi apparati, high cytoplasmic densities of mitochondria, and a low to moderate tendency for rough endoplasmic reticulum (RER) to align in parallel stacks. A1 cell bodies were commonly juxtaposed to TH-positive and TH-negative neurons, myelinated profiles, glia and/or vascular elements, but close membrane appositions were only seen with glial elements. Synaptic input to A1 neurons was predominantly asymmetric, provided virtually exclusively by non-TH-ir terminals, and directed principally to dendritic shafts; A1 somata are relatively sparsely innervated. In a second experiment, silver-intensified immunogold localization of TH-ir was combined with immunoperoxidase labeling for anterogradely transported Phaseolus vulgaris-leucoagglutinin (PHA-L), following tracer injections in the caudal aspect of the medial division of the NTS. These experiments revealed a small proportion of PHA-L-labeled axon terminals that made asymmetric contacts with dendritic shafts of TH-ir neurons. These results suggest that the fine structure and synaptic input of A1 neurons are somewhat distinct from that of rostrally situated C1 catecholamine cells. In addition, while they document a direct NTS-A1 projection that may participate in the interoceptive control of vasopressin secretion, the bulk of ventrolaterally directed projections from the caudomedial NTS contact noncatecholaminergic elements in the A1 region, some of which may correspond to so-called depressor neurons implicated in the baroreflex control of sympathetic outflow and vasopressin secretion.

Animals↗
PubMed1977

Group models, group dynamics, sociological and psychological aspects of group formation and evaluation.

Several group models are defined: a mechanistic model, a model of conflicts, a cybernetic model, a field-theoretical model, an organismic model, an interactionistic model. In all these models the group is a dynamic entity which is based on a mutual dependence of the members. From this sociological-horizontal-interactional point of view the group is therefore an entity. From a psychological-vertical aspect the group is rather a common situation in which the individual members remain in their experience separated from each other. To understand the group therapeutic dynamics it is necessary to keep in mind these two levels. From the sociological aspect, e.g. the frequency and kinds of interactions, the relationship of the inside-distances between the members to the distances of the members to the outside is decisive for group cohesion. The more the total interaction in a group augments, the more the emotionally loaded interactions increase. The significance of group cohesion in the therapeutic process is documented also by means of standardized rating scales. The normative effect of the group, the different roles in it, the group structure have to be considered if the group is to be used as a therapeutic mean. From the psychological point of view five phases of group development can be differentiated: 1) explorative contact, 2) regression, 3) catharsis, 4) insight, 5) social learning. By a factor analysis Lieberman et al. have found out that independent of the method used, the following types of group leaders were successful: the "provider", the "social engineer", the "energizer".

Group Processes↗
PubMed2002

Group beneficial norms can spread rapidly in a structured population.

Group beneficial norms are common in human societies. The persistence of such norms is consistent with evolutionary game theory, but existing models do not provide a plausible explanation for why they are common. We show that when a model of imitation used to derive replicator dynamics in isolated populations is generalized to allow for population structure, group beneficial norms can spread rapidly under plausible conditions. We also show that this mechanism allows recombination of different group beneficial norms arising in different populations.

Altruism↗
PubMed2006

Velocity of detonation at any initial density without using heat of formation of explosives.

The simplest method is introduced for reliable estimating the detonation velocity of large class of CHNO explosives based elemental composition and specific structural groups. There is no need to use heat of formation and the other experimental data for calculation of detonation velocity in the new procedure. Only elemental composition and the number of special structural groups without using heat of formation of explosive is sufficient for reliable desk calculation of detonation velocity. The results show good agreement with experimental values with respect to computed results obtained by complex computer code using BKWS and BKWR equations of state. Predicted velocities of detonation have root-mean-square (rms) percent deviation of 2.2, 5.9 and 5.3 from experimental data for new method, BKWS and BKWR equations of state, respectively.

Explosions↗
PubMed2006

Palladium complexes of a phosphorus ylide with two stabilizing groups: synthesis, structure, and DFT study of the bonding modes.

The phosphorus ylide ligand [Ph3P=C(CO2Me)C(=NPh)CO2Me] (L1) has been prepared and fully characterized by spectroscopic, crystallographic, and density functional theory (DFT) methods (B3LYP level). The reactivity of L1 toward several cationic Pd(II) and Pt(II) precursors, with two vacant coordination sites, has been studied. The reaction of [M(C/\X)(THF)2]ClO4 with L1 (1:1 molar ratio) gives [M(C/\X)(L1)]ClO4 [M = Pd, C/\X = C6H4CH2NMe2 (1), S-C6H4C(H)MeNMe2 (2), CH2-8-C9H6N (3), C6H4-2-NC5H4 (4), o-CH2C6H4P(o-tol)2 (6), eta3-C3H5 (7); M = Pt, C/\X = o-CH2C6H4P(o-tol)2 (5); M(C/\X) = Pd(C6F5)(SC4H8) (8), PdCl2 (9)]. In complexes 1-9, the ligand L1 bonds systematically to the metal center through the iminic N and the carbonyl O of the stabilizing CO2Me group, as is evident from the NMR data and from the X-ray structure of 3. Ligand L1 can also be orthopalladated by reaction with Pd(OAc)2 and LiCl, giving the dinuclear derivative [Pd(mu-Cl)(C6H4-2-PPh2=C(CO2Me)C(CO2Me)=NPh)]2 (10). The X-ray crystal structure of 10 is also reported. In none of the prepared complexes 1-10 was the C(alpha) atom found to be bonded to the metal center. DFT calculations and Bader analysis were performed on ylide L1 and complex 9 and its congeners in order to assess the preference of the six-membered N,O metallacycle over the four-membered C,N and five-membered C,O rings. The presence of two stabilizing groups at the ylidic C causes a reduction of its bonding capabilities. The increasing strength of the Pd-C, Pd-O, and Pd-N bonds along with other subtle effects are responsible for the relative stabilities of the different bonding modes.

Journal Article↗