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941.
Sylvain Robin Denisio M. Togashi Alan G. Ryder J. Gerard Wall 《Journal of bacteriology》2009,191(4):1162-1168
In eubacteria, trigger factor (TF) is the first chaperone to interact with newly synthesized polypeptides and assist their folding as they emerge from the ribosome. We report the first characterization of a TF from a psychrophilic organism. TF from Psychrobacter frigidicola (TFPf) was cloned, produced in Escherichia coli, and purified. Strikingly, cross-linking and fluorescence anisotropy analyses revealed it to exist in solution as a monomer, unlike the well-characterized, dimeric E. coli TF (TFEc). Moreover, TFPf did not exhibit the downturn in reactivation of unfolded GAPDH (glyceraldehyde-3-phosphate dehydrogenase) that is observed with its E. coli counterpart, even at high TF/GAPDH molar ratios and revealed dramatically reduced retardation of membrane translocation by a model recombinant protein compared to the E. coli chaperone. TFPf was also significantly more effective than TFEc at increasing the yield of soluble and functional recombinant protein in a cell-free protein synthesis system, indicating that it is not dependent on downstream systems for its chaperoning activity. We propose that TFPf differs from TFEc in its quaternary structure and chaperone activity, and we discuss the potential significance of these differences in its native environment. 相似文献
942.
943.
944.
Responses of canopy duration to temperature changes in four temperate tree species: relative contributions of spring and autumn leaf phenology 总被引:1,自引:0,他引:1
Yann Vitasse Annabel Josée Porté Antoine Kremer Richard Michalet Sylvain Delzon 《Oecologia》2009,161(1):187-198
While changes in spring phenological events due to global warming have been widely documented, changes in autumn phenology,
and therefore in growing season length, are less studied and poorly understood. However, it may be helpful to assess the potential
lengthening of the growing season under climate warming in order to determine its further impact on forest productivity and
C balance. The present study aimed to: (1) characterise the sensitivity of leaf phenological events to temperature, and (2)
quantify the relative contributions of leaf unfolding and senescence to the extension of canopy duration with increasing temperature,
in four deciduous tree species (Acer pseudoplatanus, Fagus sylvatica, Fraxinus excelsior and Quercus petraea). For 3 consecutive years, we monitored the spring and autumn phenology of 41 populations at elevations ranging from 100
to 1,600 m. Overall, we found significant altitudinal trends in leaf phenology and species-specific differences in temperature
sensitivity. With increasing temperature, we recorded an advance in flushing from 1.9 ± 0.3 to 6.6 ± 0.4 days °C−1 (mean ± SD) and a 0 to 5.6 ± 0.6 days °C−1 delay in leaf senescence. Together both changes resulted in a 6.9 ± 1.0 to 13.0 ± 0.7 days °C−1 lengthening of canopy duration depending on species. For three of the four studied species, advances in flushing were the
main factor responsible for lengthening canopy duration with increasing temperature, leading to a potentially larger gain
in solar radiation than delays in leaf senescence. In contrast, for beech, we found a higher sensitivity to temperature in
leaf senescence than in flushing, resulting in an equivalent contribution in solar radiation gain. These results suggest that
climate warming will alter the C uptake period and forest productivity by lengthening canopy duration. Moreover, the between-species
differences in phenological responses to temperature evidenced here could affect biotic interactions under climate warming. 相似文献
945.
Background
During the last ten years, major advances have been made in characterizing and understanding the evolution of mitochondrial DNA, the most popular marker of molecular biodiversity. Several important results were recently reported using mammals as model organisms, including (i) the absence of relationship between mitochondrial DNA diversity and life-history or ecological variables, (ii) the absence of prominent adaptive selection, contrary to what was found in invertebrates, and (iii) the unexpectedly large variation in neutral substitution rate among lineages, revealing a possible link with species maximal longevity. We propose to challenge these results thanks to the bird/mammal comparison. Direct estimates of population size are available in birds, and this group presents striking life-history trait differences with mammals (higher mass-specific metabolic rate and longevity). These properties make birds the ideal model to directly test for population size effects, and to discriminate between competing hypotheses about the causes of substitution rate variation. 相似文献946.
Rousseau J Klinger S Rachalski A Turgeon B Déléris P Vigneault E Poirier-Héon JF Davoli MA Mechawar N El Mestikawy S Cermakian N Meloche S 《Molecular and cellular biology》2010,30(24):5752-5763
Erk4 and Erk3 are atypical members of the mitogen-activated protein (MAP) kinase family. The high sequence identity of Erk4 and Erk3 proteins and the similar organization of their genes imply that the two protein kinases are paralogs. Recently, we have shown that Erk3 function is essential for neonatal survival and critical for the establishment of fetal growth potential and pulmonary function. To investigate the specific functions of Erk4, we have generated mice with a targeted disruption of the Mapk4 gene. We show that Erk4-deficient mice are viable and fertile and exhibit no gross morphological or physiological anomalies. Loss of Erk4 is not compensated by changes in Erk3 expression or activity during embryogenesis or in adult tissues. We further demonstrate that additional loss of Erk4 does not exacerbate the fetal growth restriction and pulmonary immaturity phenotypes of Erk3(-/-) mice and does not compromise the viability of Erk3(+/-) neonates. Interestingly, behavioral phenotyping revealed that Erk4-deficient mice manifest depression-like behavior in the forced-swimming test. Our analysis indicates that the MAP kinase Erk4 is dispensable for mouse embryonic development and reveals that Erk3 and Erk4 have acquired specialized functions through evolutionary diversification. 相似文献
947.
948.
Guillaume Calmettes Véronique Deschodt-Arsac Gilles Gouspillou Sylvain Miraux Bernard Muller Jean-Michel Franconi Eric Thiaudiere Philippe Diolez 《PloS one》2010,5(2)
Background
Hypoxic states of the cardiovacular system are undoubtedly associated with the most frequent diseases of modern time. Therefore, understanding hypoxic resistance encountered after physiological adaptation such as chronic hypoxia, is crucial to better deal with hypoxic insult. In this study, we examine the role of energetic modifications induced by chronic hypoxia (CH) in the higher tolerance to oxygen deprivation.Methodology/Principal Findings
Swiss mice were exposed to a simulated altitude of 5500 m in a barochamber for 21 days. Isolated perfused hearts were used to study the effects of a decreased oxygen concentration in the perfusate on contractile performance (RPP) and phosphocreatine (PCr) concentration (assessed by 31P-NMR), and to describe the integrated changes in cardiac energetics regulation by using Modular Control Analysis (MoCA). Oxygen reduction induced a concomitant decrease in RPP (−46%) and in [PCr] (−23%) in Control hearts while CH hearts energetics was unchanged. MoCA demonstrated that this adaptation to hypoxia is the direct consequence of the higher responsiveness (elasticity) of ATP production of CH hearts compared with Controls (−1.88±0.38 vs −0.89±0.41, p<0.01) measured under low oxygen perfusion. This higher elasticity induces an improved response of energy supply to cellular energy demand. The result is the conservation of a healthy control pattern of contraction in CH hearts, whereas Control hearts are severely controlled by energy supply.Conclusions/Significance
As suggested by the present study, the mechanisms responsible for this increase in elasticity and the consequent improved ability of CH heart metabolism to respond to oxygen deprivation could participate to limit the damages induced by hypoxia. 相似文献949.
950.
Xuejun Hu Sylvain Robin Shane O’Connell Gary Walsh J. Gerard Wall 《Applied microbiology and biotechnology》2010,87(5):1773-1782
β-galactosidase is an enzyme administered as a digestive supplement to treat lactose intolerance, a genetic condition prevalent
in most world regions. The gene encoding an acid-stable β-galactosidase potentially suited for use as a digestive supplement
was cloned from Aspergillus niger van Tiegh, sequenced and expressed in Pichia pastoris. The purified recombinant protein exhibited kinetic properties similar to those of the native enzyme and thus was also competitively
inhibited by its product, galactose, at application-relevant concentrations. In order to alleviate this product inhibition,
a model of the enzyme structure was generated based on a Penicillium sp. β-galactosidase crystal structure with bound β-galactose. This led to targeted mutagenesis of an Asp258-Ser-Tyr-Pro-Leu-Gly-Phe amino acid motif in the A. niger van Tiegh enzyme and isolation from the resultant library of a mutant β-galactosidase enzyme with reduced sensitivity to
inhibition by galactose (K
i of 6.46 mM galactose, compared with 0.76 mM for the wildtype recombinant enzyme). The mutated enzyme also exhibited an increased
K
m (3.76 mM compared to 2.21 mM) and reduced V
max (110.8 μmol min−1 mg−1 compared to 172.6 μmol min−1 mg−1) relative to the wild-type enzyme, however, and its stability under simulated fasting gastric conditions was significantly
reduced. The study nevertheless demonstrates the potential to rationally engineer the A. niger van Tiegh enzyme to relieve product inhibition and create mutants with improved, application-relevant kinetic properties
for treatment of lactose intolerance. 相似文献