Metal binding affinity and structural properties of an isolated EF-loop in a scaffold protein

To establish an approach to obtain the site-specific calcium binding affinity of EF-hand proteins, we have successfully designed a series of model proteins, each containing the EF-hand calcium-binding loop 3 of calmodulin, but with increasing numbers of Gly residues linking the loop to domain 1 of CD2. Structural analyses, using different spectroscopic methods, have shown that the host protein is able to retain its native structure after insertion of the 12-residue calcium-binding loop and retains a native thermal stability and thermal unfolding behavior. In addition, calcium binding to the engineered CD2 variants does not result in a significant change from native CD2 conformation. The CD2 variant with two Gly linkers has been shown to have the strongest metal binding affinity to Ca(II) and La(III). These experimental results are consistent with our molecular modeling studies, which suggest that this protein with the engineered EF-loop has a calmodulin-like calcium binding geometry and backbone conformation. The addition of two Gly linkers increases the flexibility of the inserted EF-loop 3 from calmodulin, which is essential for the proper binding of metal ions.

[Determination of rate constants of gas-phase reactions of alpha-pinene and beta-pinene with ozone]

alpha-pinene and beta-pinene are the most dominating species among natural terpenes. Terpenes are mainly emitted from forest trees, flowers and grass. In the lower troposphere terpenes can react fast with OH radical, ozone, NO3 radical and ground state oxygen atom. These reactions may contribute to the occurring of aerosols, peroxides (hydrogen peroxide and organic peroxide), carbon cycle (mainly CO), acid rain (organic acids, NO3- and SO4(2-), ozone and active radicals such as OH radical. Reactions with ozone occur both in the daytime and in the night. The study in this field in China began in the late 1980. The main work focus on the source emission and the experimental simulation has just started. It is most of our group's work. In this paper preliminary experimental simulation of the gas-phase reactions of alpha-pinene and beta-pinene with ozone were carried out in the quartz chamber. The rate constants of these reactions were measured using long-path Fourier transform infra-red combined with relative rate constant method. And the rate constants for the gas-phase reactions of alpha-pinene, beta-pinene with ozone were determined as 2.83 x 10(17) cm3.molecule-1.s-1 and 1.48 x 10(17) cm3.molecule-1.s-1 at 1.0 x 10(5) Pa and 296 +/- 3 K. The results are quite similar to the data from Atkinson group. No cyclohexane was added to the reaction system during the measurement to restrain the formation of OH radical. The formation of OH radical could not be quantified, so that the effect of subsidiary reactions induced by OH radical has not been calculated. In the later simulation study and model this effect should be considered.

Identification of a locus for disseminated superficial actinic porokeratosis at chromosome 12q23.2-24.1

Disseminated superficial actinic porokeratosis is an autosomal dominant cutaneous disorder characterized by many uniformly small, minimal, annular, anhidrotic, and keratotic lesions. The genetic basis for this disease is unknown. Using a genomewide search in a large Chinese family, we identified a locus at chromosome 12q23.2-24. 1 responsible for disseminated superficial actinic porokeratosis. The fine mapping study indicates that the disseminated superficial actinic porokeratosis gene is located within a 9.6 cM region between markers D12S1727 and D12S1605, with a maximum two-point LOD score of 20.53 (theta = 0.00) at D12S78. This is the first locus identified for a genetic disease where the major phenotype is porokeratosis. The study provides a map location for isolation of a gene causing disseminated superficial actinic porokeratosis.

Detection of a novel ATP-dependent cross-linked protein at the 5' splice site-U1 small nuclear RNA duplex by methylene blue-mediated photo-cross-linking

Assembly of spliceosomes involves a number of sequential steps in which small nuclear ribonucleoprotein particles (snRNPs) and some non-snRNP proteins recognize the splice site sequences and undergo various conformational rearrangements. A number of important intermolecular RNA-RNA duplexes are formed transiently during the process of splice site recognition. Various steps in the assembly pathway are dependent upon ATP hydrolysis, either for protein phosphorylation or for the activity of helicases, which may modulate the RNA structures. Major efforts have been made to identify proteins that interact with specific regions of the pre-mRNA during the stages of spliceosome assembly and catalysis by site-specific UV cross-linking. However, UV cross-linking is often inefficient for the detection of proteins that interact with base-paired RNA. Here we have used the complementary approach of methylene blue-mediated photo-cross-linking to detect specifically proteins that interact with the duplexes formed between pre-mRNA and small nuclear RNA (snRNA). We have detected a novel cross-link between a 65-kDa protein (p65) and the 5' splice site. A range of data suggest that p65 cross-links to the transient duplex formed by U1 snRNA and the 5' splice site. Moreover, although p65 cross-linking requires only a 5' splice site within the pre-mRNA, it also requires ATP hydrolysis, suggesting that its detection reflects a very early ATP-dependent event during splicing.

Crosslinking of the U5 snRNP-specific 116-kDa protein to RNA hairpins that block step 2 of splicing

Step 2 of pre-mRNA splicing has characteristics that are suggestive of a 5' to 3' scanning process from the branch point to locate the 3' splice site. Specifically, the 3' splice site is almost always at the first AG downstream of the branch point even when the two elements are separated by hundreds of nucleotides. Insertion of new AGs between the branch and 3' splice site, or mutation of the wild-type 3' splice site, usually results in use of the new first AG as the 3' splice site. Finally, insertion of stable secondary structure between the branch point and 3' splice site, but distant from both elements, results in a block to step 2. We have sought to complement this circumstantial evidence by detecting physical contacts between the spliceosome and the RNA substrate in regions that are not themselves important for splicing, other than that they lie between the branch point/polypyrimidine tract and the 3' splice site. We have blocked step 2 of splicing by insertion of hairpin structures between the branch point and 3' splice site and applied methylene blue-mediated crosslinking, which is specific for protein-dsRNA interactions. Using this approach, we have detected a 116-kDa crosslinked protein that appears after step 1 of splicing with all transcripts containing a hairpin downstream of the branch point. The protein was identified as the 116-kDa U5 snRNP protein, which is a GTP-binding protein involved in step 2 of splicing. The crosslinking characteristics of U5 p116 are consistent with it having a role in locating the 3' splice site AG prior to step 2 of splicing.

Selective DNA binding of (N-alkylamine)-substituted naphthalene imides and diimides to G+C-rich DNA

Alkylamine-substituted naphthalene imides and diimides bind DNA by intercalation and have applications as anticancer agents. The unique structures of these imides in which two adjacent carbonyl groups lie coplanar to an extended aromatic ring system allow the possibility of sequence-selective interactions between the intercalated chromophore and guanine amino groups situated in the DNA minor groove. The binding affinities of N-[3-(dimethylamino)propyl amine]-1,8-naphthalenedicarboxylic imide (N-DMPrNI) and N,N'-bis [3,3'-(dimethylamino)propylamine]-naphthalene-1,4,5,8-tetracarboxylic diimide (N-BDMPrNDI) for natural DNAs of differing base composition were determined spectroscopically and by equilibrium dialysis. In agreement with the above proposition, binding studies indicated that both the naphthalene imide and diimide strongly prefer to intercalate into steps containing at least one G:C base pair. The dependencies of association constants on DNA base composition are consistent with a requirement for one G:C pair in the binding site of the monomide, and two G:C pairs in binding sites of the diimide. These selectivities are comparable to or exceed that of actinomycin D, a classic G:C-selective drug. Protection footprinting with DNase I confirmed that the naphthalene monoiimide (N-DMPrNI) prefers to bind adjacent to G:C base pairs, with a most consistent preference for "mixed" steps containing both a G:C and an A:T pair, excepting GA:TC. Several 5'-CG-3' steps were also good binding sites as indicated by nuclease protection, but few GC:GC or GG:CC steps were protected. The naphthalene diimide inhibited DNase I digestion, but did not yield a footprint. The base recognition ability and versatile chemistry make naphthalene imides and diimides attractive building blocks for design of highly sequence-specific, DNA-directed drug candidates including conjugated oligonucleotides or oligopeptides.

Detection of double-stranded RNA-protein interactions by methylene blue-mediated photo-crosslinking

Double-stranded(ds) RNA-binding proteins have diverse functions in the cell. An obstacle to investigating the interactions between these proteins and dsRNA is the relative inefficiency of traditional UV-crosslinking methods for extended regions of dsRNA. We have therefore developed an alternative procedure for RNA-protein photo-crosslinking that efficiently induces RNA-protein crosslinks in double-stranded regions of RNA. We show that dsRNA-protein crosslinks can be induced by visible light in the presence of the dye methylene blue, which most likely mediates crosslinking by intercalating in the dsRNA helix. A recombinant dsRNA binding domain from the Drosophila staufen protein and human protein kinase R were crosslinked by UV or methylene blue to a series of dsRNAs. In each case, the degree of crosslinking was greater with methylene blue, particularly with RNAs with few single-stranded loops. Methylene blue-mediated crosslinking therefore complements and extends the existing repertoire of crosslinking methods for detecting RNA-protein interactions.

N,N'-bis[3,3'-(dimethylamino)propylamine]-3,4,9, 10-perylenetetracarboxylic diimide, a dicationic perylene dye for rapid precipitation and quantitation of trace amounts of DNA

A novel dicationic dye with a polycyclic aromatic perylene core and flexible cationic side chains- N,N'-bis[3, 3'-(dimethylamino)propylamine]-3,4,9,10-perylenetetracarboxylic diimide-termed "DAPER," was synthesized and characterized. The dye appears to exist in a highly stacked form in aqueous solution. DAPER precipitates extremely low concentrations of DNA very rapidly, efficiently, and with a stoichiometry of one tightly bound dye per DNA base pair, corresponding to a neutral complex. Precipitation may occur due to side-by-side association between the polyanionic DNA helix and polycationic dye stacks. DNA precipitation by DAPER is less sensitive to DNA concentration and length, and prevailing salt concentrations, than precipitation with ethanol or propanol. DAPER can be quantitatively extracted from DNA into a standard phenol:chloroform mixture under slightly alkaline conditions. The recovered DNA is suitable for treatment with enzymes typically used in DNA sequencing procedures. The amount of DNA precipitated is accurately determined by visible absorption or fluorescence spectroscopic analyses of the phenol:chloroform extracts. Several samples of DNA can be precipitated, recovered, and quantitated in about 1 h using standard microscale procedures and equipment. The unique qualities of DAPER provide the basis for a very sensitive, rapid, and versatile method for simultaneous precipitation and quantitation of microgram and submicrogram amounts of DNA.

Experimental study of chuanxiong on cerebrovascular hemodynamic parameters

In the experimental rabbit arteriosclerosis, the change of the cerebrovascular hemodynamic parameters (CVHP) and the effect of Chuanxiong (CX) on CVHP were observed. In arteriosclerosis group (AS group), the mean flow (Qmean), mean velocity (Vmean), maximal velocity (Vmax) and minimal velocity (Vmin) of the carotid blood flow and cerebrovascular compliance for zero pressure (CO) were significantly decreased (P < 0.05, 0.01), but the values of cerebrovascular peripheral resistance (R) and characteristic impedance (Zc) were significantly increased (P < 0.05 and 0.01), and the value of R showed significant positive correlation with the extent of carotid lesions (P < 0.01). All indexes of CVHP of the Chuanxiong group (CX group) were close to and had no significant difference from those of the normal group (N group) but Qmean, Vmean, Vmin, CO and R were significantly better than those of the AS group (P < 0.05, 0.01). These results showed that CX can effectively improve cerebrovascular hemodynamics.

Investigation of the mechanism underlying the inhibitory effect of heterologous ras genes in plant cells

The ras genes from yeast and mammalian cells were fused to plant expression promoters, and introduced into plant cells via Agrobacterium, to study their effect on cell growth and development. All introduced ras genes had a strong inhibitory effect on callus and shoot regeneration from plant tissues. This is consistent with earlier findings that heterologous ras genes were highly lethal to protoplasts following direct DNA uptake. These effects could not be reversed by increasing exogenous or endogenous cytokinin levels. These effects were also independent of the v-Ha-ras mutations in functionally important regions of Ras proteins such as effector-binding and membrane-binding sites. Similarly, co-transformation with the genes encoding the Ras-negative regulators, GTPase-activating protein and neurofibromin did not affect the ras inhibitory effect, indicating that the mechanism of ras inhibition of plant cells is not related to normal ras cellular functions. This conclusion was supported by further studies in which ras gene expression was modified using various promoters and antisense constructs. The introduced ras sequences remained fully inhibitory regardless of which promoters (inducible or tissue-specific) or which orientations (sense or antisense) were tested. This strongly suggests that the ras DNA sequence itself, rather than the Ras protein or ras mRNA, is directly involved in the inhibitory effect. The mechanism underlying this novel phenomenon remains unknown. Introduced ras genes may inhibit plant cell growth by inducing co-suppression of unknown endogenous ras or ras-related genes, thereby leading to the arrest of cell growth.

Structural alterations in desferrioxamine compatible with iron clearance in animals

The design, synthesis, and biological evaluation of amideless desferrioxamine analogues are described. The design concept is predicated on the idea that a low molecular weight desferrioxamine analogue would represent a better pharmacophore from which to construct an orally effective or more efficient trihydroxamate than the parent chelator. The study demonstrates that (1) the monohydroxamate units of desferrioxamine must be linked to promote iron clearance, (2) the N-propanoyl-N-pentyl fragments of desferrioxamine can be replaced with smaller, e.g., C-5, methylene units without compromising the analogue's iron-clearing properties, and (3) a delicate balance exists between the molecule's iron-clearing efficiency and its lipophilicity.

Single amino acid substitution alters T cell determinant selection during antigen processing of Staphylococcus aureus nuclease

The effect of amino acid residues outside of T cell determinant regions of Staphylococcus aureus nuclease (Nase) on the activation of T cell hybridomas has been investigated. T cell hybridomas derived from BALB/c mice immunized with Nase were screened against a nested set of overlapping synthetic peptides spanning the entire Nase molecule. Five regions of Nase, encompassing residues 1 to 20, 21 to 40, 61 to 80, 101 to 120, and 112 to 130, were found to be the T cell determinants. Region 61 to 80 is the immunodominant site. Mutants of Nase with a single amino acid substitution outside the defined T cell determinants were tested for their ability to stimulate the T cell hybridomas. The substitution of arginine for glutamic acid at residue 43 markedly reduces the antigenic potency of the protein for I-Ed restricted T cell hybridomas, which recognize Nase peptides comprised of residues 21 to 40 (p21-40) or 112 to 130 (p112-130). In contrast, the stimulatory capacity of this mutant for I-Ad restricted T cell hybridomas remains unchanged. Our results suggest that selective regulation of an immune response may be achieved by appropriately mutagenizing protein Ag.

Single amino acid substitution alters T cell determinant selection during antigen processing of Staphylococcus aureus nuclease

The effect of amino acid residues outside of T cell determinant regions of Staphylococcus aureus nuclease (Nase) on the activation of T cell hybridomas has been investigated. T cell hybridomas derived from BALB/c mice immunized with Nase were screened against a nested set of overlapping synthetic peptides spanning the entire Nase molecule. Five regions of Nase, encompassing residues 1 to 20, 21 to 40, 61 to 80, 101 to 120, and 112 to 130, were found to be the T cell determinants. Region 61 to 80 is the immunodominant site. Mutants of Nase with a single amino acid substitution outside the defined T cell determinants were tested for their ability to stimulate the T cell hybridomas. The substitution of arginine for glutamic acid at residue 43 markedly reduces the antigenic potency of the protein for I-Ed restricted T cell hybridomas, which recognize Nase peptides comprised of residues 21 to 40 (p21-40) or 112 to 130 (p112-130). In contrast, the stimulatory capacity of this mutant for I-Ad restricted T cell hybridomas remains unchanged. Our results suggest that selective regulation of an immune response may be achieved by appropriately mutagenizing protein Ag.

The influence of N2-O2 and He-O2 saturation diving on electroencephalogram of human bodies

This paper reports the changes of the EEG of human bodies during saturation exposure at different depths to different mixed gases. The results of the research show that the most obvious on EEG was the appearance of diffused slow waves, usually theta waves of 4-7 times/s, and delta waves of 2-3 times/s within individual subjects. The EEG changes at 50 m were more obvious than those at 36.5 m. With the prolonging of time under high pressure, the EEG had some improvements, for instance, the slow waves decreased and the alpha waves increased. There was a certain relationship between these changes and the symptoms which appeared in the human body. The chief factor of the EEG changes is due to the effect of nitrogen narcosis during the oxygen-nitrogen diving experiment. In addition, carbon dioxide retention under the high pressure is also a factor of the EEG changes, because repeated inhaling of CO2-dense mixtures could aggravate the EEG changes and the reduction of carbon dioxide in humans by hyperventilation could improve abnormal EEGs. The main changes of the EEG during the helium-oxygen exposure at 302 m were the increase of theta waves, and even of delta waves, the decrease in alpha rhythm and the decline of amplitude of alpha waves. Increased theta index and decreased alpha index could be seen at the depth of 302 m. Under any of the above-mentioned pressure conditions when slow waves characteristic of abnormal changes appeared in the EEGs, the EEGs could be temporarily improved by photic stimulation, i.e. slow waves disappeared and alpha waves reappeared. When photic stimulation was over, alpha waves disappeared and slow waves reappeared. It was indicated that abnormal changes of the EEG under high pressure were a kind of temporary and reversible changes of the brain function.

Aortic compliance in human hypertension

Aortic compliance in normotensive and hypertensive Chinese subjects undergoing diagnostic cardiac catheterization was compared by using a newly described method that allows for determination of the pressure dependence of compliance if one assumes a value for the exponential coefficient of the pressure-volume relation of the large arteries. Under baseline conditions in the normotensive and hypertensive groups at mean aortic pressures of 96.3 and 128.6 mm Hg, aortic compliance averaged 1.47 and 0.80 ml/mm Hg, respectively. Compliance in the hypertensive group at a diastolic pressure of 99.4 mm Hg (which was nearly equal to the mean normotensive pressure) was 1.072 ml/mm Hg--still significantly lower than in the normotensive group. During nitroprusside infusion, however, the compliances in the hypertensive group increased to levels equal to or greater those in the normotensive group. Thus, these data confirm that aortic compliance is lower in hypertensive than in normotensive humans. They further demonstrate that the lower compliance cannot be attributed entirely to the elevated blood pressure, suggesting that excess smooth muscle tone may be partly responsible.

Estimating arterial resistance and compliance during transient conditions in humans

Almost all existing methods for estimating hemodynamic parameters are valid only during steady-state conditions. There is often a need, however, for estimating peripheral resistance and total arterial compliance during beat-to-beat transients such as during atrial fibrillation. During such transients the pressure at the onset and end of a cardiac cycle usually differ. This pressure difference necessitates a modification of usual methods used for estimating these hemodynamic parameters. In this paper we formulate a method for estimating resistance and total arterial compliance during such beat-to-beat transients. For simplicity the expressions are derived for a two-element windkessel model of the circulation. The method is a generalization of one we previously proposed. Rather than using parameter estimation techniques or having to assume a monoexponential pressure decay during diastole, our method uses the areas under the systolic and diastolic portions of the aortic pressure versus time tracing to obtain explicit expressions for compliance; both for the case where it is constant and when it is assumed to be nonlinear (exponential) function of pressure. Aortic pressure and flow data from patients undergoing cardiac catheterization are employed to illustrate the method. Results illustrate the quantitative difference between uncorrected and corrected estimates of both resistance and compliance as a function of the pressure difference between the onset and end of each beat. The uncorrected parameters were found to be linearly and highly correlated with these pressure differences. Regressions of pressure difference against normalized values revealed that the pooled data for all patients defined a single relationship.(ABSTRACT TRUNCATED AT 250 WORDS)

Impedance of arterial system simulated by viscoelastic t tubes terminated in windkessels

An improved asymmetric t-tube model of the arterial system is proposed. The model consists of two viscoelastic tubes of differing lengths, each terminated in a modified windkessel with inductance as well as resistance and compliance. Equations for calculating the input impedance of this model are presented. Using typical data from the literature, the model predicts a more realistic impedance modulus and phase than previous models of the circulation. Parametric analysis shows that when peripheral compliances are altered, sharp peaks in the very low frequency portions of the impedance spectra are produced, whereas alterations of either the characteristic impedances or inductances of the terminations have little effect on input impedance. Alteration of the elasticity or relative lengths of the tubes results in shifts in the positions of the maxima and minima akin to those observed experimentally. Change in the viscosity of the walls or of the blood only affects the fluctuations of the impedance spectra without affecting the positions of the maxima and minima. Thus, with this still simple model, very realistic impedance spectra are obtainable. The model provides more insight than previously proposed models into the individual influence of various parameters of the proximal and peripheral vasculature on central hemodynamics.

Beta-2-microglobulin synthesis is increased during activation of human monocytes

We have investigated the regulation of beta 2-microglobulin (beta 2-M) synthesis by monocytes. Recent interest in beta 2-M has developed since the discovery that this protein forms amyloid fibrils in patients undergoing long-term, chronic hemodialysis. The beta 2-M amyloidosis is linked to the greatly elevated levels of monomeric beta 2-M in their circulation. Since factors that govern beta 2-M release from plasma membranes are not known, we endeavored to evaluate beta 2-M release during monocyte activation. Utilizing a human monocyte-like cell line, U937, we studied the effect of bacterial toxin stimulation on levels of membrane, cell surface, and supernatant beta 2-M. We now present a novel method to purify beta 2-M, a solid-phase radioimmunoassay to measure soluble beta 2-M, and an ELISA to measure membrane beta 2-M. Using these methods we found that the levels of beta 2-M in the cell membrane or on the cell surface did not change during monocyte activation. However, activation did induce a significant increase in the concentration of beta 2-M in monocyte supernatants, indicating that beta 2-M synthesis by monocytes is increased during monocyte activation. These results suggest that monocyte activation by hemodialysis membranes may be a contributing factor to the observed increase in circulating beta 2-M levels.

Normalization of hemodynamic parameters: application to vascular resistance and impedance

Comparison of hemodynamic parameters among different species is complicated by the wide variety of body sizes and shapes. Although some parameters such as blood pressure and flow velocity seem to have similar absolute values among species, most other parameters such as cardiac output, pulse wave velocity, and heart rate vary greatly. Comparisons would be facilitated if one uses indices that are independent of body size and/or shape. An ideal index will bring values for individuals or species of different sizes into the same range and yet exhibit large relative changes to responses to small increments of an intervention in an individual. In this paper we demonstrate how dimensional analysis together with Buckingham's pi theorem and the assumption of biological similarity can be used to derive dimensionless hemodynamic normalization indices. Using data from the literature and from our own laboratory, we illustrate the approach by examining resistance and impedance. We compare our results with previously proposed methods of accounting for different body sizes, namely, dividing impedance by resistance or vice versa, multiplying by body weight, and using flow velocity rather than volume flow in the calculations. Both of our proposed indices bring the values for arterial and pulmonary resistance and impedance for rats, rabbits, dogs, and humans into the same range, although the variability among species using our indices is twice that of those previously proposed. On the other hand, the relative changes of our two indices induced by vasoactive agents or exercise in a dog are from two to five times greater than either the absolute values themselves or the previously used indices.