14 research outputs found

    Introduction: What we do and do not know regarding redox processes of thiols in signaling pathways

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    Due to their susceptibility towards redox modification, protein thiols represent primary targets for the modulation of protein activity, conformation and oligomerization. Until fairly recently, such modifications were considered “damage” as a result of oxidative stress, before researchers recognized their physiological importance for biologic signaling. This paradigm shift, and the associated necessity to accurately characterize and quantify the various pathways of thiol redox modifications not only for specific proteins, but also within the cellular environment, has enticed researchers to take a close look at the impact of environment and molecular (protein) structure on these reactions. This Special Issue on Redox Biology of Thiols in Signaling Pathways is the result of a workshop organized at the 2013 Annual Meeting of the Society for Free Radical Biology and Medicine in San Antonio, Texas, summarizing the contributions from many of the presenters. It will provide a stimulating synopsis on what is known, and what is not known, about the reaction mechanisms which underlie the role of thiols and oxidative processes in signaling pathways

    Protein thiyl radical reactions and product formation: a kinetic simulation

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    Protein thiyl radicals are important intermediates generated in redox processes of thiols and disulfides. Thiyl radicals efficiently react with glutathione and ascorbate, and the common notion is that these reactions serve to eliminate thiyl radicals before they can enter potentially hazardous processes. However, over the past years increasing evidence has been provided for rather efficient intramolecular hydrogen transfer processes of thiyl radicals in proteins and peptides. Based on rate constants published for these processes, we have performed kinetic simulations of protein thiyl radical reactivity. Our simulations suggest that protein thiyl radicals enter intramolecular hydrogen transfer reactions to a significant extent even under physiologic conditions, i.e. in the presence of 30 μM oxygen, 1 mM ascorbate and 10 mM glutathione. At lower concentrations of ascorbate and glutathione, frequently observed when tissue is exposed to oxidative stress, the extent of irreversible protein thiyl radical-dependent protein modification increases

    Singlet oxygen inactivates protein tyrosine phosphatase-1B by oxidation of the active site cysteine

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    Singlet oxygen (1O2), an electronically excited form of molecular oxygen, is a mediator of biological effects of ultraviolet A radiation, stimulating signaling cascades in human cells. We demonstrate here that 1O2 generated by photosensitization or by thermodecomposition of 3,3′-(1,4-naphthylidene)dipropionate-1,4-endoperoxide inactivates isolated protein tyrosine phosphatases (PTPases). PTPase activities of PTP1B or CD45 were abolished by low concentrations of 1O2, but were largely restored by post-treatment with dithiothreitol. Electrospray ionization mass spectrometry analysis of tryptic digests of PTP1B exposed to 1O2 revealed oxidation of active-site Cys215 as the only cysteine residue oxidized. In summary, 1O2 may activate signaling cascades by interfering with phosphotyrosine dephosphorylation.This study was supported by Deutsche Forschungsgemeinschaft (Bonn, Germany; Sonderforschungsbereich 503, Project B1). H.S. is a Fellow of the National Foundation for Cancer Research, Bethesda, MD, USA

    Myeloperoxidase-derived oxidants inhibit sarco/endoplasmic reticulum Ca2+-ATPase activity, and perturb Ca2+ homeostasis in human coronary artery endothelial cells

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    The sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) plays a critical role in Ca2+ homeostasis via sequestration of this ion into the sarco/endoplasmic reticulum. The activity of this pump is inhibited by oxidants and impaired in ageing tissues and cardiovascular disease. We have shown previously that the myeloperoxidase- (MPO) derived oxidants HOCl and HOSCN target thiols and mediate cellular dysfunction. As SERCA contains Cys residues critical to ATPase activity, we hypothesized that HOCl and HOSCN might inhibit SERCA activity, via thiol oxidation, and increase cytosolic Ca2+ levels in human coronary artery endothelial cells (HCAEC). Exposure of sarcoplasmic reticulum vesicles to pre-formed or enzymatically-generated HOCl and HOSCN resulted in a concentration-dependent decrease in ATPase activity; this was also inhibited by the SERCA inhibitor thapsigargin. Decomposed HOSCN and incomplete MPO enzyme systems did not decrease activity. Loss of ATPase activity occurred concurrently with oxidation of SERCA Cys residues and protein modification. Exposure of HCAEC, with or without external Ca2+, to HOSCN or HOCl, resulted in a time- and concentration-dependent increase in intracellular Ca2+ under conditions that did not result in immediate loss of cell viability. Thapsigargin, but not inhibitors of plasma membrane or mitochondrial Ca2+ pumps/channels, completely attenuated the increase in intracellular Ca2+ consistent with a critical role for SERCA in maintaining endothelial cell Ca2+ homeostasis. Angiotensin II pre-treatment potentiated the effect of HOSCN at low concentrations. MPO-mediated modulation of intracellular Ca2+ levels may exacerbate endothelial dysfunction, a key early event in atherosclerosis, and be more marked in smokers due to their higher SCN− levels

    Loss of Conformational Stability in Calmodulin upon Methionine Oxidation

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    We have used electrospray ionization mass spectrometry (ESI-MS), circular dichroism (CD), and fluorescence spectroscopy to investigate the secondary and tertiary structural consequences that result from oxidative modification of methionine residues in wheat germ calmodulin (CaM), and prevent activation of the plasma membrane Ca-ATPase. Using ESI-MS, we have measured rates of modification and molecular mass distributions of oxidatively modified CaM species (CaMox) resulting from exposure to H2O2. From these rates, we find that oxidative modification of methionine to the corresponding methionine sulfoxide does not predispose CaM to further oxidative modification. These results indicate that methionine oxidation results in no large-scale alterations in the tertiary structure of CaMox, because the rates of oxidative modification of individual methionines are directly related to their solvent exposure. Likewise, CD measurements indicate that methionine oxidation results in little change in the apparent α-helical content at 28°C, and only a small (0.3 ± 0.1 kcal mol−1) decrease in thermal stability, suggesting the disruption of a limited number of specific noncovalent interactions. Fluorescence lifetime, anisotropy, and quenching measurements of N-(1-pyrenyl)-maleimide (PMal) covalently bound to Cys26 indicate local structural changes around PMal in the amino-terminal domain in response to oxidative modification of methionine residues in the carboxyl-terminal domain. Because the opposing globular domains remain spatially distant in both native and oxidatively modified CaM, the oxidative modification of methionines in the carboxyl-terminal domain are suggested to modify the conformation of the amino-terminal domain through alterations in the structural features involving the interdomain central helix. The structural basis for the linkage between oxidative modification and these global conformational changes is discussed in terms of possible alterations in specific noncovalent interactions that have previously been suggested to stabilize the central helix in CaM

    State of the climate in 2018

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    In 2018, the dominant greenhouse gases released into Earth’s atmosphere—carbon dioxide, methane, and nitrous oxide—continued their increase. The annual global average carbon dioxide concentration at Earth’s surface was 407.4 ± 0.1 ppm, the highest in the modern instrumental record and in ice core records dating back 800 000 years. Combined, greenhouse gases and several halogenated gases contribute just over 3 W m−2 to radiative forcing and represent a nearly 43% increase since 1990. Carbon dioxide is responsible for about 65% of this radiative forcing. With a weak La Niña in early 2018 transitioning to a weak El Niño by the year’s end, the global surface (land and ocean) temperature was the fourth highest on record, with only 2015 through 2017 being warmer. Several European countries reported record high annual temperatures. There were also more high, and fewer low, temperature extremes than in nearly all of the 68-year extremes record. Madagascar recorded a record daily temperature of 40.5°C in Morondava in March, while South Korea set its record high of 41.0°C in August in Hongcheon. Nawabshah, Pakistan, recorded its highest temperature of 50.2°C, which may be a new daily world record for April. Globally, the annual lower troposphere temperature was third to seventh highest, depending on the dataset analyzed. The lower stratospheric temperature was approximately fifth lowest. The 2018 Arctic land surface temperature was 1.2°C above the 1981–2010 average, tying for third highest in the 118-year record, following 2016 and 2017. June’s Arctic snow cover extent was almost half of what it was 35 years ago. Across Greenland, however, regional summer temperatures were generally below or near average. Additionally, a satellite survey of 47 glaciers in Greenland indicated a net increase in area for the first time since records began in 1999. Increasing permafrost temperatures were reported at most observation sites in the Arctic, with the overall increase of 0.1°–0.2°C between 2017 and 2018 being comparable to the highest rate of warming ever observed in the region. On 17 March, Arctic sea ice extent marked the second smallest annual maximum in the 38-year record, larger than only 2017. The minimum extent in 2018 was reached on 19 September and again on 23 September, tying 2008 and 2010 for the sixth lowest extent on record. The 23 September date tied 1997 as the latest sea ice minimum date on record. First-year ice now dominates the ice cover, comprising 77% of the March 2018 ice pack compared to 55% during the 1980s. Because thinner, younger ice is more vulnerable to melting out in summer, this shift in sea ice age has contributed to the decreasing trend in minimum ice extent. Regionally, Bering Sea ice extent was at record lows for almost the entire 2017/18 ice season. For the Antarctic continent as a whole, 2018 was warmer than average. On the highest points of the Antarctic Plateau, the automatic weather station Relay (74°S) broke or tied six monthly temperature records throughout the year, with August breaking its record by nearly 8°C. However, cool conditions in the western Bellingshausen Sea and Amundsen Sea sector contributed to a low melt season overall for 2017/18. High SSTs contributed to low summer sea ice extent in the Ross and Weddell Seas in 2018, underpinning the second lowest Antarctic summer minimum sea ice extent on record. Despite conducive conditions for its formation, the ozone hole at its maximum extent in September was near the 2000–18 mean, likely due to an ongoing slow decline in stratospheric chlorine monoxide concentration. Across the oceans, globally averaged SST decreased slightly since the record El Niño year of 2016 but was still far above the climatological mean. On average, SST is increasing at a rate of 0.10° ± 0.01°C decade−1 since 1950. The warming appeared largest in the tropical Indian Ocean and smallest in the North Pacific. The deeper ocean continues to warm year after year. For the seventh consecutive year, global annual mean sea level became the highest in the 26-year record, rising to 81 mm above the 1993 average. As anticipated in a warming climate, the hydrological cycle over the ocean is accelerating: dry regions are becoming drier and wet regions rainier. Closer to the equator, 95 named tropical storms were observed during 2018, well above the 1981–2010 average of 82. Eleven tropical cyclones reached Saffir–Simpson scale Category 5 intensity. North Atlantic Major Hurricane Michael’s landfall intensity of 140 kt was the fourth strongest for any continental U.S. hurricane landfall in the 168-year record. Michael caused more than 30 fatalities and 25billion(U.S.dollars)indamages.InthewesternNorthPacific,SuperTyphoonMangkhutledto160fatalitiesand25 billion (U.S. dollars) in damages. In the western North Pacific, Super Typhoon Mangkhut led to 160 fatalities and 6 billion (U.S. dollars) in damages across the Philippines, Hong Kong, Macau, mainland China, Guam, and the Northern Mariana Islands. Tropical Storm Son-Tinh was responsible for 170 fatalities in Vietnam and Laos. Nearly all the islands of Micronesia experienced at least moderate impacts from various tropical cyclones. Across land, many areas around the globe received copious precipitation, notable at different time scales. Rodrigues and Réunion Island near southern Africa each reported their third wettest year on record. In Hawaii, 1262 mm precipitation at Waipā Gardens (Kauai) on 14–15 April set a new U.S. record for 24-h precipitation. In Brazil, the city of Belo Horizonte received nearly 75 mm of rain in just 20 minutes, nearly half its monthly average. Globally, fire activity during 2018 was the lowest since the start of the record in 1997, with a combined burned area of about 500 million hectares. This reinforced the long-term downward trend in fire emissions driven by changes in land use in frequently burning savannas. However, wildfires burned 3.5 million hectares across the United States, well above the 2000–10 average of 2.7 million hectares. Combined, U.S. wildfire damages for the 2017 and 2018 wildfire seasons exceeded $40 billion (U.S. dollars)
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