Phosphoribosyl pyrophosphate synthetase from Escherichia coli was cloned, purified, and crystal- lized. Single crystals of the enzyme were grown under microgravity. The X-ray diffraction data set was col- lected at the Spring-8 synchrotron facility and used to determine the three-dimensional structure of the enzyme by the molecular-replacement method at 2.71 Å resolution. The active and regulatory sites in the molecule of E. coli phosphoribosyl pyrophosphate synthetase were revealed by comparison with the homol- ogous protein from Bacillus subtilis, the structure of which was determined in a complex with functional ligands. The conformations of polypeptide-chain fragments surrounding and composing the active and reg- ulatory sites were shown to be identical in both proteins.
Three-dimensional structure of carboxypeptidase T from Thermoactinomyces vulgaris in complex with N-BOC-L-leucine
The 3D structure of recombinant bacterial carboxypeptidase T (CPT) in complex with N-BOC-L-leucine was determined at 1.38 A resolution. Crystals for the X-ray study were grown in microgravity using the counter-diffusion technique. N-BOC-L-leucine and SO4(2-) ion bound in the enzyme active site were localized in the electron density map. Location of the leucine side chain in CPT-N-BOC-L-leucine complex allowed identification of the S1 subsite of the enzyme, and its structure was determined. Superposition of the structures of CPT-N-BOC-L-leucine complex and complexes of pancreatic carboxypeptidases A and B with substrate and inhibitors was carried out, and similarity of the S1 subsites in these three carboxypeptidases was revealed. It was found that SO4(2-) ion occupies the same position in the S1′ subsite as the C-terminal carboxy group of the substrate.
This paper will explore the opportunities and challenges in developing the commercial market in LEO through the ISS program and all its facets, including operations, mission support activities, utilization, and contracting. The role of NASA-funded research in the vertical translation of basic research in space to practical application in the market or to other government service agencies will also be addressed. Other aspects, including government regulation, investment and tax incentives, and possible roles of various government agencies will also be explored. Of particular importance, the role of private industry, currently in the supply business, in the development of the demand for LEO capabilities and services beyond the federal government will be highlighted. In conclusion, this paper will address the prospects in reaching the goal of commercializing LEO starting from where we are today in human spaceflight and the International Space Station.
Observation of radiation environment in the International Space Station in 2012–March 2013 by Liulin-5 particle telescope
Since June 2007 the Liulin-5 charged particle telescope, located in the spherical tissue-equivalent phantom of the MATROSHKA-R project onboard the International Space Station (ISS), has been making measurements of the local energetic particle radiation environment. From 27 December 2011 to 09 March 2013 measurements were conducted in and outside the phantom located in the MIM1 module of the ISS. In this paper Liulin-5 dose rates, due to galactic cosmic rays and South Atlantic Anomaly trapped protons, measured during that period are presented. Particularly, dose rates and particle fluxes for the radiation characteristics in the phantom during solar energetic particle (SEP) events occurring in March and May 2012 are discussed. Liulin-5 SEP observations are compared with other ISS data, GOES proton fluxes as well as with solar energetic particle measurements obtained onboard the Mir space station during previous solar cycles.
Characteristics of local human skeleton responses to microgravity and drug treatment for osteoporosis in clinic
Analysis of the results of long term investigations of bones in cosmonauts on board Mir orbital sta tion(OS) and International Space Station (ISS) (n = 80) was performed. Theoretically predicted (evolution ary predefined) change in mass of different skeleton bones was found to be correlated (r = 0.904) with the position relative to Earth’s gravity vector. Vector dependence of bone loss results from local specificity of expression of bone metabolism genes, which reflects mechanical prehistory of skeleton structures in the evo lution of Homo erectus. Genetic polymorphism is accountable for high individual variability of bone loss, which is attested by the dependence of bone loss rate on polymorphism of certain genetic markers of bone metabolism. The type of the orbital vehicle did not affect the individual specific stability of the bone loss ratio in different segments of the skeleton. This fact is considered as a phenotype fingerprint of local metabolism in the form of a locus specific spatial structure of distribution of non collagen proteins responsible for posi tion regulation of endosteal metabolism. Drug treatment of osteoporosis (n = 107) evidences that recovery rate depends on bone location; the most likely reason is different effectiveness of local osteotropic interven tion into areas of bustling resorption.
Survival of Antarctic Cryptoendolithic Fungi in Simulated Martian Conditions On Board the International Space Station
Dehydrated Antarctic cryptoendolithic communities and colonies of the rock inhabitant black fungi Cryomyces antarcticus (CCFEE 515) and Cryomyces minteri (CCFEE 5187) were exposed as part of the Lichens and Fungi Experiment (LIFE) for 18 months in the European Space Agency’s EXPOSE-E facility to simulated martian conditions aboard the International Space Station (ISS). Upon sample retrieval, survival was proved by testing colony-forming ability, and viability of cells (as integrity of cell membrane) was determined by the propidium monoazide (PMA) assay coupled with quantitative PCR tests. Although less than 10% of the samples exposed to simulated martian conditions were able to proliferate and form colonies, the PMA assay indicated that more than 60% of the cells and rock communities had remained intact after the "Mars exposure." Furthermore, a high stability of the DNA in the cells was demonstrated. The results contribute to assessing the stability of resistant microorganisms and biosignatures on the surface of Mars, data that are valuable information for further search-for-life experiments on Mars.
Intrinsic cardiovascular autonomic regulatory system of astronauts exposed long-term to microgravity in space: observational study
The fractal scaling of the long-term heart rate variability (HRV) reflects the ‘intrinsic’ autonomic regulatory system. Herein, we examine how microgravity on the ISS affected the power-law scaling β (beta) of astronauts during a long-duration (about 6 months) spaceflight. Ambulatory electrocardiographic (ECG) monitoring was performed on seven healthy astronauts (5 men, 52.0 ± 4.2 years of age) five times: before launch, 24 ± 5 (F01) and 73 ± 5 (F02) days after launch, 15 ± 5 days before return (F03), and after return to Earth. The power-law scaling β was calculated as the slope of the regression line of the power density of the MEM spectrum versus frequency plotted on a log10–log10 scale in the range of 0.0001–0.01 Hz (corresponding to periods of 2.8 h to 1.6 min). β was less negative in space (−0.949 ± 0.061) than on Earth (−1.163 ± 0.075; P o 0.025). The difference was more pronounced during the awake than during the rest/sleep span. The circadian amplitude and acrophase (phase of maximum) of β did not differ in space as compared with Earth. An effect of microgravity was detected within 1 month (F01) in space and continued throughout the spaceflight. The intrinsic autonomic regulatory system that protects life under serious environmental conditions on Earth is altered in the microgravity environment, with no change over the 6-month spaceflight. It is thus important to find a way to improve conditions in space and/or in terms of human physiology, not to compromise the intrinsic autonomic regulatory system now that;plans are being made to inhabit another planet in the near future.
Huntington’s disease is caused by expansion of a polyglutamine (polyQ) repeat in the huntingtin protein. A structural basis for the apparent transition between normal and disease-causing expanded polyQ repeats of huntingtin is unknown. The "linear lattice" model proposed random-coil structures for both normal and expanded polyQ in the preaggregation state. Consistent with this model, the affinity and stoichiometry of the anti-polyQ antibody MW1 increased with the number of glutamines. An opposing "structural toxic threshold" model proposed a conformational change above the pathogenic polyQ threshold resulting in a specific toxic conformation for expanded polyQ. Support for this model was provided by the anti-polyQ antibody 3B5H10, which was reported to specifically recognize a distinct pathologic conformation of soluble expanded polyQ. To distinguish between these models, we directly compared binding of MW1 and 3B5H10 to normal and expanded polyQ repeats within huntingtin exon 1 fusion proteins. We found similar binding characteristics for both antibodies. First, both antibodies bound to normal, as well as expanded, polyQ in huntingtin exon 1 fusion proteins. Second, an expanded polyQ tract contained multiple epitopes for fragments antigen-binding (Fabs) of both antibodies, demonstrating that 3B5H10 does not recognize a single epitope specific to expanded polyQ. Finally, small-angle X-ray scattering and dynamic light scattering revealed similar binding modes for MW1 and 3B5H10 Fab-huntingtin exon 1 complexes. Together, these results support the linear lattice model for polyQ binding proteins, suggesting that the hypothesized pathologic conformation of soluble expanded polyQ is not a valid target for drug design.
Abstract: Hackney, KJ, Scott, JM, Hanson, AM, English, KL, Downs, ME, and Ploutz-Snyder, LL. The astronaut-athlete: optimizing human performance in space. J Strength Cond Res 29(12): 3531–3545, 2015—It is well known that long-duration spaceflight results in deconditioning of neuromuscular and cardiovascular systems, leading to a decline in physical fitness. On reloading in gravitational environments, reduced fitness (e.g., aerobic capacity, muscular strength, and endurance) could impair human performance, mission success, and crew safety. The level of fitness necessary for the performance of routine and off-nominal terrestrial mission tasks remains an unanswered and pressing question for scientists and flight physicians. To mitigate fitness loss during spaceflight, resistance and aerobic exercise are the most effective countermeasure available to astronauts. Currently, 2.5 h·d−1, 6–7 d·wk−1 is allotted in crew schedules for exercise to be performed on highly specialized hardware on the International Space Station (ISS). Exercise hardware provides up to 273 kg of loading capability for resistance exercise, treadmill speeds between 0.44 and 5.5 m·s−1, and cycle workloads from 0 and 350 W. Compared to ISS missions, future missions beyond low earth orbit will likely be accomplished with less vehicle volume and power allocated for exercise hardware. Concomitant factors, such as diet and age, will also affect the physiologic responses to exercise training (e.g., anabolic resistance) in the space environment. Research into the potential optimization of exercise countermeasures through use of dietary supplementation, and pharmaceuticals may assist in reducing physiological deconditioning during long-duration spaceflight and have the potential to enhance performance of occupationally related astronaut tasks (e.g., extravehicular activity, habitat construction, equipment repairs, planetary exploration, and emergency response).
Pulse transit time measured by photoplethysmography improves the accuracy of heart rate as a surrogate measure of cardiac output, stroke volume and oxygen uptake in response to graded exercise
Heart rate (HR) is a valuable and widespread measure for physical training programs, although its description of conditioning is limited to the cardiac response to exercise. More comprehensive measures of exercise adaptation include cardiac output (Q), stroke volume (SV) and oxygen uptake (VO2), but these physiological parameters can be measured only with cumbersome equipment installed in clinical settings. In this work, we explore the ability of pulse transit time (PTT) to represent a valuable pairing with HR for indirectly estimating Q, SV and VO2 non-invasively. PTT was measured as the time interval between the peak of the electrocardiographic (ECG) R-wave and the onset of the photoplethysmography (PPG) waveform at the periphery (i.e. fingertip) with a portable sensor. Fifteen healthy young subjects underwent a graded incremental cycling protocol after which HR and PTT were correlated with Q, SV and VO2 using linear mixed models. The addition of PTT significantly improved the modeling of Q, SV and VO2 at the individual level ([Formula: see text] for SV, 0.548 for Q, and 0.771 for VO2) compared to predictive models based solely on HR ([Formula: see text] for SV, 0.503 for Q, and 0.745 for VO2). While challenges in sensitivity and artifact rejection exist, combining PTT with HR holds potential for development of novel wearable sensors that provide exercise assessment largely superior to HR monitors.