Absence of kinetic thermal stabilization in a hyperthermophile rubredoxin indicated by 40 microsecond folding in the presence of irreversible denaturation

The striking kinetic stability of many proteins derived from hyperthermophilic organisms has led to the proposal that such stability may result from a heightened activation barrier for unfolding independent of a corresponding increase in the thermodynamic stability. This in turn implies a corresponding retardation of the folding reaction. A commonly cited model for kinetic thermal stabilization is the rubredoxin from Pyrococcus furiosus (Pf), which exhibits an irreversible denaturation lifetime at 100 degrees C of nearly a week. Utilizing protein resonances shifted well outside of the random coil chemical shift envelope, nuclear magnetic resonance (NMR) chemical exchange measurements on Pf rubredoxin as well as on the mesophile Clostridium pasteurianum (Cp) rubredoxin demonstrate reversible thermal transition temperatures of 144 degrees C (137 degrees C for the N-terminal modified A2K variant) and 104 degrees C, respectively, with similar (un)folding rates of approximately 25,000 s(-1), only modestly slower than the diffusion controlled rate. The absence of a substantial activation barrier to rubredoxin folding as well as the similar folding kinetics of the mesophile protein indicate that kinetic stabilization has not been utilized by the hyperthermophile rubredoxin in achieving its extreme thermal stability. The two-state folding kinetics observed for Pf rubredoxin contradict a previous assertion of multiphasic folding based on hydrogen exchange data extrapolated to an estimated midpoint of transition temperature (T(m)) of nearly 200 degrees C. This discrepancy is resolved by the observation that the base-catalyzed hydrogen exchange of the model dipeptide (N-acetyl-L-cysteine-N-methylamide)4-Cd2+ is 23-fold slower than that of the free cysteine model dipeptide used to normalize the Pf rubredoxin hydrogen exchange data.     

T-cell senescence: a culprit of immune abnormalities in chronic inflammation and persistent infection

Long-lived clonal T cells deficient in CD28 expression are commonly found in patients with inflammatory syndromes and persistent infections. Considering that CD28 loss is the most consistent immunological marker of aging, we propose that, in pathological states, CD28(null) T cells represent prematurely senescent cells resulting from persistent immune activation. These unusual lymphocytes have aberrant functions that contribute to disease-related immune abnormalities, and the degree of accumulation of CD28(null) T cells predicts the severity of clinical manifestations. We suggest that understanding of the biological properties of T cells that have reached replicative senescence will influence the future management of certain diseases. Indeed, studies on the molecular basis for the loss of CD28 are already providing information on methods to functionally rescue senescent T cells.     

Synoviocyte-mediated expansion of inflammatory T cells in rheumatoid synovitis is dependent on CD47-thrombospondin 1 interaction

Fibroblast-like synoviocytes (FLS) from patients with rheumatoid arthritis elicit spontaneous proliferation of autologous T cells in an HLA-DR and CD47 costimulation-dependent manner. T cell costimulation through CD47 is attributed to specific interaction with thrombospondin-1 (TSP1), a CD47 ligand displayed on FLS. CD47 binding by FLS has broad biological impact that includes adhesion and the triggering of specific costimulatory signals. TSP1(+) FLS are highly adhesive to T cells and support their aggregation and growth in situ. Long-term cultures of T cells and FLS form heterotypic foci that are amenable to propagation without exogenous growth factors. T cell adhesion and aggregate formation on TSP1(+) FLS substrates are inhibited by CD47-binding peptides. In contrast, FLS from arthroscopy controls lack adhesive or T cell growth-promoting activities. CD47 stimulation transduces a costimulatory signal different from that of CD28, producing a gene expression profile that included induction of ferritin L chain, a component of the inflammatory response. Ferritin L chain augments CD3-induced proliferation of T cells. Collectively, these results demonstrate the active role of FLS in the recruitment, activation, and expansion of T cells in a CD47-dependent manner. Because TSP1 is abundantly expressed in the rheumatoid synovium, CD47-TSP1 interaction is proposed to be a key component of an FLS/T cell regulatory circuit that perpetuates the inflammatory process in the rheumatoid joint.     

Truncation of the carboxyl terminus of the dihydropyridine receptor beta1a subunit promotes Ca2+ dependent excitation-contraction coupling in skeletal myotubes

We investigated the contribution of the carboxyl terminus region of the beta1a subunit of the skeletal dihydropyridine receptor (DHPR) to the mechanism of excitation-contraction (EC) coupling. cDNA-transfected beta1 KO myotubes were voltage clamped, and Ca(2+) transients were analyzed by confocal fluo-4 fluorescence. A chimera with an amino terminus half of beta2a and a carboxyl terminus half of beta1a (beta2a 1-287/beta1a 325-524) recapitulates skeletal-type EC coupling quantitatively and was used to generate truncated variants lacking 7 to 60 residues from the beta1a-specific carboxyl terminus (Delta7, Delta21, Delta29, Delta35, and Delta60). Ca(2+) transients recovered by the control chimera have a sigmoidal Ca(2+) fluorescence (DeltaF/F) versus voltage curve with saturation at potentials more positive than +30 mV, independent of external Ca(2+) and stimulus duration. In contrast, the amplitude of Ca(2+) transients expressed by the truncated variants varied with the duration of the pulse, and for Delta29, Delta35, and Delta60, also varied with external Ca(2+) concentration. For Delta7 and Delta21, a 50-ms depolarization produced a sigmoidal DeltaF/F versus voltage curve with a lower than control maximum fluorescence. Moreover, for Delta29, Delta35, and Delta60, a 200-ms depolarization increased the maximum fluorescence and changed the shape of the DeltaF/F versus voltage curve, from sigmoidal to bell-shaped, with a maximum at approximately +30 mV. The change in voltage dependence, together with the external Ca(2+) dependence and additional controls with ryanodine, indicated a loss of skeletal-type EC coupling and the emergence of an EC coupling component triggered by the Ca(2+) current. Analyses of d(DeltaF/F)/dt showed that the rate of cytosolic Ca(2+) increase during the Ca(2+) transient was fivefold faster for the control chimera than for the severely truncated variants (Delta29, Delta35, and Delta60) and was consistent with the kinetics of the DHPR Ca(2+) current. In summary, absence of the beta1a-specific carboxyl terminus (last 29 to 60 residues of the control chimera) results in a loss of the fast component of the Ca(2+) transient, bending of the DeltaF/F versus voltage curve, and emergence of EC coupling triggered by the Ca(2+) current. The studies underscore the essential role of the carboxyl terminus region of the DHPR beta1a subunit in fast voltage dependent EC coupling in skeletal myotubes.     

Hybridization screening of very short PCR products for paleoepidemiological studies of Chagas' disease

Single strands of very short PCR products can be covalently immobilized to a slide and then easily detected by probe hybridization. In this work, the PCR product was a 70-nucleotide segment of ancient DNA, representing a portion of repeat mini-circle DNA from the kinetoplast of Trypanosoma cruzi, the infectious agent of Chagas' disease (American Trypanosomiasis). The target segment was initially established to be present in soft tissue samples taken from four "naturally" mummified Andean bodies using PCR followed by cloning and sequencing. Hybridization screening of the covalently immobilized PCR products positively identified products from 25 of 27 specimens of different tissues from these four mummies. The method appears to be ideal for the purpose of screening a large number of specimens when the target PCR product is very short.     

Escherichia coli LPS-induced LV dysfunction: role of toll-like receptor-4 in the adult heart

The precise molecular mechanisms responsible for sepsis-induced myocardial dysfunction remain undefined. Toll-like receptor-4 (TLR-4) engages lipopolysaccharide (LPS) and activates signaling pathways leading to the expression of proinflammatory cytokines implicated in myocardial dysfunction. We determined whether TLR-4 was necessary for LPS-induced myocardial dysfunction in vivo. The effects of LPS on left ventricular (LV) function were studied in mice with defective TLR-4 signaling (C3H/HeJ, TLR-4 deficient) and wild-type mice (C3HeB/FeJ). Mice (n = 5/group) were injected with LPS or diluent, and LV function was examined by using two-dimensional echocardiography and conductance catheters. LPS significantly decreased all indexes of LV function in wild-type mice when compared with controls; LV function was not depressed in the LPS-treated TLR-4-deficient mice relative to controls. LPS increased myocardial nitric oxide synthase-2 expression and cGMP only in wild-type mice. This study suggests that TLR-4 mediates the LV dysfunction that occurs in LPS-induced shock. Therefore, TLR-4 might be a therapeutic target for attenuating the effects of LPS on the heart.     

CO2 efflux from a Mediterranean semi-arid forest soil. I. Seasonality and effects of stoniness

We studied the seasonality of total soil CO₂efflux and labeled C-CO₂ released from ¹⁴Clabeled straw incubated in the H horizon of asemi-arid Mediterranean forest soil. Fieldmeasurements were carried out over 520 days in aseries of reconstructed soil profiles with and withouta gravel layer below the H horizon. We monitored soilclimate and related this to soil CO₂ efflux.Seasonal variations in soil CO₂ efflux in asemiarid Mediterranean forest were mainly related tochanges in soil temperature. In spite of drought, highrespiration rates were observed in mid summer. Highsoil CO₂ efflux in hot and dry episodes wasattributed to increases in soil biological activity.The minimum soil CO₂ efflux occurred in latesummer also under dry conditions, probably related toa decrease in soil biological activity in deephorizons. Biological activity in organic layers waslimited by water potential () in summer and bytemperature in winter. Rewetting a dry soil resultedin large increases in soil CO₂ efflux only at hightemperatures. These large increases represented asignificant contribution to the decomposition oforganic matter in the uppermost horizons. Soilbiological activity in the uppermost horizons was moresensitive to changes in soil and hence tosummer rainstorms than the bulk soil microbialactivity. The presence of a layer of gravel improvedboth moisture and temperature conditions for thedecomposition of organic matter. As a result, soilCO₂ efflux increased in soils containing rockfragments. These effects were especially large for theorganic layers.     

Genetic mapping of quantitative trait loci affecting susceptibility to Marek's disease virus induced tumors in F2 intercross chickens.

Marek''s disease (MD) is a lymphoproliferative disease caused by the MD virus (MDV), which costs the poultry industry nearly $1 billion annually. To identify quantitative trait loci (QTL) affecting MD susceptibility, the inbred lines 6(3) (MD resistant) and 7(2) (MD susceptible) were mated to create more than 300 F2 chickens. The F2 chickens were challenged with MDV JM strain, moderately virulent) at 1 wk of age and assessed for MD susceptibility. The QTL analysis was divided into three stages. In stage 1, 65 DNA markers selected from the chicken genetic maps were typed on the 40 most MD-susceptible and the 40 most MD-resistant F2 chickens, and 21 markers residing near suggestive QTL were revealed by analysis of variance (ANOVA). In stage 2, the suggestive markers plus available flanking markers were typed on 272 F2 chickens, and three suggestive QTL were identified by ANOVA. In stage 3, using the interval mapping program Map Manager and permutation tests, two significant and two suggestive MD QTL were identified on four chromosomal subregions. Three to five loci collected explained between 11 and 23% of the phenotypic MD variation, or 32-68% of the genetic variance. This study constitutes the first report in the domestic chicken on the mapping of non-major histocompatibility complex QTL affecting MD susceptibility.