The EPR spectrum of tyrosine Z* and its decay kinetics in O2-evolving photosystem II preparations

The O2-evolving complex of photosystem II, Mn 4Ca, cycles through five oxidation states, S0,..., S4, during its catalytic function, which involves the gradual abstraction of four electrons and four protons from two bound water molecules. The direct oxidant of the complex is the tyrosine neutral radical, YZ(*), which is transiently produced by the highly oxidizing power of the photoexcited chlorophyll species P680. EPR characterization of YZ(*) has been limited, until recently, to inhibited (non-oxygen-evolving) preparations. A number of relatively recent papers have demonstrated the trapping of YZ(*) in O2-evolving preparations at liquid helium temperatures as an intermediate of the S0 to S1, S1 to S2, and S2 to S3 transitions. The respective EPR spectra are broadened and split at g approximately 2 by the magnetic interaction with the Mn cluster, but this interaction collapses at temperatures higher than about 100K [Zahariou et al. (2007) Biochemistry 46, 14335 -14341]. We have conducted a study of the Tyr Z(*) transient in the temperature range 77-240 K by employing rapid or slow EPR scans. The results reveal for the first time high-resolution X-band spectra of Tyr Z(*) in the functional system and at temperatures close to the onset of the S-state transitions. We have simulated the S 2Y Z(*) spectrum using the simulation algorithm of Svistunenko and Cooper [(2004) Biophys. J. 87, 582 -595]. The small g(x) = 2.00689 value inferred from the analysis suggests either a H-bonding of Tyr Z (*) (presumably with His190) that is stronger than what has been assumed from studies of Tyr D(*) or Tyr Z(*) in Mn-depleted preparations or a more electropositive environment around Tyr Z(*). The study has also yielded for the first time direct information on the temperature variation of the YZ(*)/QA(-) recombination reaction in the various S states. The reaction follows biphasic kinetics with the slow phase dominating at low temperatures and the fast phase dominating at high temperatures. It is tentatively proposed that the slow phase represents the action of the YZ(*)/YZ(-) redox couple while the fast phase represents that of the YZ(*)/YZH couple; it is inferred that Tyr Z at elevated temperatures is protonated at rest. It is also proposed that YZ(*)/YZH is the couple that oxidizes the Mn cluster during the S1-S2 and S2-S3 transitions. A simple mechanism ensuring a rapid (concerted) protonation of Tyr Z upon oxidation of the Mn cluster is discussed, and also, a structure-based molecular model suggesting the participation of His190 into two hydrogen bonds is proposed.     

Surfactant gene polymorphisms and interstitial lung diseases

Pulmonary surfactant is a complex mixture of phospholipids and proteins, which is present in the alveolar lining fluid and is essential for normal lung function. Alterations in surfactant composition have been reported in several interstitial lung diseases (ILDs). Furthermore, a mutation in the surfactant protein C gene that results in complete absence of the protein has been shown to be associated with familial ILD. The role of surfactant in lung disease is therefore drawing increasing attention following the elucidation of the genetic basis underlying its surface expression and the proof of surfactant abnormalities in ILD.     

Temperature responses of carbon mineralization in conifer forest soils from different regional climates incubated under standard laboratory conditions

¹⁴C‐labelled straw was mixed with soils collected from seven coniferous forests located on a climatic gradient in Western Europe ranging from boreal to Mediterranean conditions. The soils were incubated in the laboratory at 4°, 10°, 16°, 23° and 30 °C with constant moisture over 550 days. The temperature coefficient (Q₁₀) for straw carbon mineralization decreased with increasing incubation temperatures. This was a characteristic of all the soils with a difference of two Q₁₀ units between the 4–10° and the 23? 30 °C temperature ranges. It was also found that the magnitude of the temperature response function was related to the period of soil incubation. Initial temperature responses of microbial communities were different to those shown after a long period of laboratory incubation and may have reflected shifts in microbial species composition in response to changes in the temperature regime. The rapid exhaustion of the labile fractions of the decomposing material at higher temperatures could also lead to underestimation of the temperature sensitivity of soils unless estimated for carbon pools of similar qualities. Finally, the thermal optima for the organic soil horizons (Of and Oh) were lower than 30 °C even after 550 days of incubation. It was concluded that these responses could not be attributed to microbial physiological adaptations, but rather to the rates at which recalcitrant microbial secondary products were formed at higher temperatures. The implication of these variable temperature responses of soil materials is discussed in relation to modelling potential effects of global warming.     

Highly Invasive Listeria monocytogenes Strains Have Growth and Invasion Advantages in Strain Competition

Multiple Listeria monocytogenes strains can be present in the same food sample; moreover, infection with more than one L. monocytogenes strain can also occur. In this study we investigated the impact of strain competition on the growth and in vitro virulence potential of L. monocytogenes. We identified two strong competitor strains, whose growth was not (or only slightly) influenced by the presence of other strains and two weak competitor strains, which were outcompeted by other strains. Cell contact was essential for growth inhibition. In vitro virulence assays using human intestinal epithelial Caco2 cells showed a correlation between the invasion efficiency and growth inhibition: the strong growth competitor strains showed high invasiveness. Moreover, invasion efficiency of the highly invasive strain was further increased in certain combinations by the presence of a low invasive strain. In all tested combinations, the less invasive strain was outcompeted by the higher invasive strain. Studying the effect of cell contact on in vitro virulence competition revealed a complex pattern in which the observed effects depended only partially on cell-contact suggesting that competition occurs at two different levels: i) during co-cultivation prior to infection, which might influence the expression of virulence factors, and ii) during infection, when bacterial cells compete for the host cell. In conclusion, we show that growth of L. monocytogenes can be inhibited by strains of the same species leading potentially to biased recovery during enrichment procedures. Furthermore, the presence of more than one L. monocytogenes strain in food can lead to increased infection rates due to synergistic effects on the virulence potential.     

p-Curve and p-Hacking in Observational Research

The p-curve, the distribution of statistically significant p-values of published studies, has been used to make inferences on the proportion of true effects and on the presence of p-hacking in the published literature. We analyze the p-curve for observational research in the presence of p-hacking. We show by means of simulations that even with minimal omitted-variable bias (e.g., unaccounted confounding) p-curves based on true effects and p-curves based on null-effects with p-hacking cannot be reliably distinguished. We also demonstrate this problem using as practical example the evaluation of the effect of malaria prevalence on economic growth between 1960 and 1996. These findings call recent studies into question that use the p-curve to infer that most published research findings are based on true effects in the medical literature and in a wide range of disciplines. p-values in observational research may need to be empirically calibrated to be interpretable with respect to the commonly used significance threshold of 0.05. Violations of randomization in experimental studies may also result in situations where the use of p-curves is similarly unreliable.     

Combination of reduced oxygen tension and intermittent hydrostatic pressure: a useful tool in articular cartilage tissue engineering.

Cartilage cells are normally studied under atmospheric pressure conditions and without loading. However, since cartilage exists in a condition of reduced oxygen and intermittent hydrostatic pressure we hypothesized lower partial oxygen pressures (PO2) and different intermittent hydrostatic pressures (IHP) would increase articular chondrocyte proliferation and matrix production and to stabilize chondrocyte phenotype in vitro. Monolayers of adult bovine articular chondrocytes were cultured under 5% or 21% PO2 in combination with IHP (0.2 MPa amplitude, frequencies 5/5s = 0.1 Hz, 30/2 or 2/30 min on/off loading). We measured proliferation (3H-thymidine incorporation) and collagen secretion (protein-binding assay, collagen type II-ELISA and immunocytochemical staining of pericellular collagen types I, II and IX). Reduced PO2 stimulated proliferation and collagen type II and IX secretion of chondrocytes in comparison to 21% PO2. Additionally, collagen type I expression was delayed by low PO2, indicating a stabilization of the cell phenotype. IHP 5/5s and 30/2 min inhibited proliferation but increased collagen secretion (pericellular collagen type IX was decreased). IHP 30/2 min delayed first expression of collagen type I. In contrast, IHP 2/30 min increased proliferation, but lowered collagen expression. All stimulating or inhibiting effects of PO2 and IHP were additive and vice versa. Reduced PO2 and different settings of IHP increased proliferation, collagen secretion, and phenotype stability of chondrocytes. The oxygen- and IHP-induced effects were additive, suggesting that a combination of these parameters might be a useful tool in cartilage tissue engineering.     

ANG II AT1 and AT2 receptors both inhibit bFGF-induced proliferation of bovine adrenocortical cells

Angiotensin II(ANG II) has long been known for its pressor and growth-promotingeffects, which are both mediated by theAT₁ receptor. By contrast, theAT₂ receptor has recently beenreported to mediate inhibition of proliferation through as yetundefined mechanisms. We report here that in bovine adrenal fasciculata cells ANG II by itself does not affect growth but inhibits basic fibroblast growth factor (bFGF)-induced DNA synthesis and blocks thecells in G₁ phase. Consistent withthis, ANG II inhibits cyclin D₁ expression and cyclinD₁-associated kinase activity. Theantimitogenic effect of ANG II is partly mimicked by theAT₂-selective agonist CGP-42112.It is also blocked partly and in an additive fashion by theAT₁- andAT₂-selective antagonists losartanand PD-123319, indicating the contribution of both receptor subtypes tothis response. AT₁-dependentantiproliferation is selectively blocked by the cyclooxygenaseinhibitor indomethacin and restored by prostaglandin E₂, whereasAT₂-receptor-mediated inhibitionof growth is suppressed by the tyrosine phosphatase inhibitorsorthovanadate and bpV(pic). Both pathways are, however,pertussis toxin sensitive. We hypothesize that, in fasciculatacells, the AT₁ receptor inhibitsbFGF-induced proliferation by stimulating prostaglandin synthesis,whereas the AT₂ receptor mediatesits effect through a pathway that requires protein tyrosine phosphataseactivation.