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Functional Mechanism (functional + mechanism)
Selected AbstractsConformational properties of bacterial DnaK and yeast mitochondrial Hsp70FEBS JOURNAL, Issue 12 2005-helical subdomain, Role of the divergent C-terminal Among the eukaryotic members of the Hsp70 family, mitochondrial Hsp70 shows the highest degree of sequence identity with bacterial DnaK. Although they share a functional mechanism and homologous co-chaperones, they are highly specific and cannot be exchanged between Escherichia coli and yeast mitochondria. To provide a structural basis for this finding, we characterized both proteins, as well as two DnaK/mtHsp70 chimeras constructed by domain swapping, using biochemical and biophysical methods. Here, we show that DnaK and mtHsp70 display different conformational and biochemical properties. Replacing different regions of the DnaK peptide-binding domain with those of mtHsp70 results in chimeric proteins that: (a) are not able to support growth of an E. coli DnaK deletion strain at stress temperatures (e.g. 42 °C); (b) show increased accessibility and decreased thermal stability of the peptide-binding pocket; and (c) have reduced activation by bacterial, but not mitochondrial co-chaperones, as compared with DnaK. Importantly, swapping the C-terminal ,-helical subdomain promotes a conformational change in the chimeras to an mtHsp70-like conformation. Thus, interaction with bacterial co-chaperones correlates well with the conformation that natural and chimeric Hsp70s adopt in solution. Our results support the hypothesis that a specific protein structure might regulate the interaction of Hsp70s with particular components of the cellular machinery, such as Tim44, so that they perform specific functions. [source] Osteopontin promotes gastric cancer metastasis by augmenting cell survival and invasion through Akt-mediated HIF-1, up-regulation and MMP9 activationJOURNAL OF CELLULAR AND MOLECULAR MEDICINE, Issue 8b 2009Gang Song Abstract Osteopontin (OPN) is a secreted, integrin-binding matrix phosphorylated glycoprotein. OPN has been shown to facilitate the progression and metastasis of malignancies and has prognostic value in several types of cancer, including gastric cancer. However, the functional mechanism of OPN mediated metastatic growth in gastric cancer remains unclear. Here, using multiple in vitro and in vivo models, we report that OPN strongly promoted the progression and metastasis of gastric cancer. Immunohistochemical staining revealed that OPN, matrix metalloproteinase (MMP)9 and hypoxia-inducible factor (HIF)-1, have statistically significant different expression patterns between well- and poorly differentiated tissue samples (P < 0.05). Correlations existed between OPN and MMP9, and between OPN and HIF-1, (r1= 0.872, p1 < 0.01 and r2= 0.878, p2 < 0.01). Furthermore, OPN dramatically increased colony formation and invasion of gastric cancer cells in vitro and promoted tumour growth and metastasis in vivo. In addition, OPN potently protected gastric cancer cells from serum depletion-induced apoptosis. Further study shows that OPN activated phosphoinositide 3-kinase/Akt survival pathway and up-regulated HIF-1,via binding to ,v,3 integrins in gastric cancer cells. Moreover, we found that OPN could activate MMP9 and up-regulate MMP2. Taken together, our results suggest that the survival-promoting function is crucial for OPN to promote the development of gastric cancer, and HIF-1, and MMP9 may play key roles during this process. Thus, targeting OPN and its related signalling network may develop an effective therapeutic approach for the management of gastric cancer. [source] Pro-metastasis function of TGF, mediated by the smad pathwayJOURNAL OF CELLULAR BIOCHEMISTRY, Issue 6 2006Yibin Kang Abstract The transforming growth factor beta (TGF,) signaling pathway plays a vital role in the development and homeostasis of normal tissues. Abnormal function of this pathway contributes to the initiation and progression of cancer. Smad proteins are key signal transducers of the TGF, pathway and are essential for the growth suppression function of TGF,. Smads are bona fide tumor suppressors whose mutation, deletion, and silencing are associated with many types of human cancer. However, the involvement and functional mechanism of Smad proteins in cancer metastasis are poorly defined. Recent studies using genetically modified cancer cells and mouse tumor models have provided concrete evidence for a Smad-dependent mechanism for metastasis promotion by TGF,. Understanding the dual roles of Smad proteins in tumor initiation and progression has important implications for cancer therapeutics. J. Cell. Biochem. © 2006 Wiley-Liss, Inc. [source] Nitrogen and carbon source,sink relationships in trees at the Himalayan treelines compared with lower elevationsPLANT CELL & ENVIRONMENT, Issue 10 2008MAI-HE LI ABSTRACT No single hypothesis or theory has been widely accepted for explaining the functional mechanism of global alpine/arctic treeline formation. The present study tested whether the alpine treeline is determined by (1) the needle nitrogen content associated with photosynthesis (carbon gain); (2) a sufficient source,sink ratio of carbon; or (3) a sufficient C,N ratio. Nitrogen does not limit the growth and development of trees studied at the Himalayan treelines. Levels of non-structural carbohydrates (NSC) in trees were species-specific and site-dependent; therefore, the treeline cases studied did not show consistent evidence of source/carbon limitation or sink/growth limitation in treeline trees. However, results of the combined three treelines showed that the treeline trees may suffer from a winter carbon shortage. The source capacity and the sink capacity of a tree influence its tissue NSC concentrations and the carbon balance; therefore, we suggest that the persistence and development of treeline trees in a harsh alpine environment may require a minimum level of the total NSC concentration, a sufficiently high sugar:starch ratio, and a balanced carbon source,sink relationship. [source] The potential for soluble and transport loss of particulate aquaculture wastesAQUACULTURE RESEARCH, Issue 10 2000M F Tlusty The relative potential for soluble and transport losses of aquaculture waste was examined. The waste was collected at four junctures between introduction to the environment and the culmination of settlement, including samples of feed, faeces, particulate matter in the water column obtained from sediment traps, and the benthos. Organic matter was used as a model system to investigate the fate of these components because it was simple to analyse and previous research has found it to be correlated to carbon and nutrient levels in the samples. A narrow definition of each loss was considered. Soluble losses were examined by measuring change in organic matter content while the samples were in a stationary water field. The potential for transport losses was examined by determining if light and heavy fractions of a sample differed in their amount of organic matter. Faecal matter had a very high solubility potential, and lost approximately 50% of its organic matter in 12 days. No other sample had losses >,10%. The benthic samples gained organic matter while sitting in the stationary water field. There was no discernible trend to the samples' potential for transport losses. However, for all replicates combined, the smaller the proportion of the lighter fraction, the greater the difference (+) in the organic matter content between the light and heavy fractions. Thus, lighter material is the last to settle and thus more prone to be transported further afield. The implications of this study include the need for model studies to examine different types of loss and also elucidation of divergent degradation properties of each component. This study also points to a functional mechanism behind greater environmental impacts associated with poorly managed farms. [source] Structure of the C subunit of V-type ATPase from Thermus thermophilus at 1.85,Å resolutionACTA CRYSTALLOGRAPHICA SECTION D, Issue 5 2004Nobutaka Numoto The V-type H+ -ATPases are similar to the F-type ATP synthases in their structure and functional mechanism. They hydrolyze ATP coupled with proton translocation across a membrane, but in some archaea and eubacteria they also synthesize ATP in the reverse reaction. The C subunit is one of the components of the membrane-bound V0 moiety of V-type ATPases. The C subunit of V-type H+ -ATPase from Thermus thermophilus was crystallized in a monoclinic form and its crystal structure was determined at 1.85,Å resolution by the MAD method using selenomethionyl protein. The structure has a cone (tapered cylinder) shape consisting of only two types of helix (long and short) as secondary-structure elements. The molecule is divided into three similar domains, each of which has essentially the same topology. On the basis of the structural features and molecular-surface charge distribution, it is suggested that the bottom side of the C subunit is a possible binding site for the V0 proteolipid L-subunit ring and that the C subunit might function as a spacer unit between the proteolipid L-subunit ring and the rotating V1 central shaft. [source] The effect of genetic variation in the type 1 deiodinase gene on the interindividual variation in serum thyroid hormone levels: an investigation in healthy Danish twinsCLINICAL ENDOCRINOLOGY, Issue 6 2009Wendy M. Van Der Deure Summary Introduction, Genetic factors have a considerable influence on serum thyroid hormone levels. The C785T and A1814G polymorphisms, located in the 3, untranslated region of the type 1 deiodinase (D1) gene have been associated with serum FT4 and rT3 levels. Objective, In healthy Danish twins, we examined the association of these polymorphisms with serum thyroid hormone levels and determined the proportion of genetic influence explained by these variants. We analysed the underlying functional mechanism by performing mRNA stability measurements and analysed the effect of these variants on D1 activity. Methods, Serum thyroid measurements and genotypes of the D1-C785T and D1-A1814G polymorphisms were determined in 1192 twins. Structural equation modelling was used to determine heritability estimates. Functional analyses were carried out in D1-transfected JEG3 cells. Results, Carriers of the D1-785T allele had 3·8% higher FT4 and 14·3% higher rT3 levels, resulting in a lower T3/T4 and T3/rT3 ratio and a higher rT3/T4 ratio. This polymorphism explained 0·87% and 1·79%, respectively, of the variation in serum FT4 and rT3. The D1-A1814G polymorphism was not associated with serum thyroid hormone levels. No differences in D1 mRNA decay rate or D1 activity were observed between wild-type D1 and the two variants. Conclusion, The D1-C785T polymorphism is consistently and significantly associated with serum thyroid hormone levels. However, the proportion of genetic influence explained by this particular polymorphism is small. No effect of the polymorphism on D1 mRNA decay rate or D1 activity was observed. The underlying functional mechanism needs to be elucidated. [source] On functional motor adaptations: from the quantification of motor strategies to the prevention of musculoskeletal disorders in the neck,shoulder regionACTA PHYSIOLOGICA, Issue 2010P. Madeleine Abstract Background:, Occupations characterized by a static low load and by repetitive actions show a high prevalence of work-related musculoskeletal disorders (WMSD) in the neck,shoulder region. Moreover, muscle fatigue and discomfort are reported to play a relevant initiating role in WMSD. Aims: To investigate relationships between altered sensory information, i.e. localized muscle fatigue, discomfort and pain and their associations to changes in motor control patterns. Materials & Methods:, In total 101 subjects participated. Questionnaires, subjective assessments of perceived exertion and pain intensity as well as surface electromyography (SEMG), mechanomyography (MMG), force and kinematics recordings were performed. Results:, Multi-channel SEMG and MMG revealed that the degree of heterogeneity of the trapezius muscle activation increased with fatigue. Further, the spatial organization of trapezius muscle activity changed in a dynamic manner during sustained contraction with acute experimental pain. A graduation of the motor changes in relation to the pain stage (acute, subchronic and chronic) and work experience were also found. The duration of the work task was shorter in presence of acute and chronic pain. Acute pain resulted in decreased activity of the painful muscle while in subchronic and chronic pain, a more static muscle activation was found. Posture and movement changed in the presence of neck,shoulder pain. Larger and smaller sizes of arm and trunk movement variability were respectively found in acute pain and subchronic/chronic pain. The size and structure of kinematics variability decreased also in the region of discomfort. Motor variability was higher in workers with high experience. Moreover, the pattern of activation of the upper trapezius muscle changed when receiving SEMG/MMG biofeedback during computer work. Discussion:, SEMG and MMG changes underlie functional mechanisms for the maintenance of force during fatiguing contraction and acute pain that may lead to the widespread pain seen in WMSD. A lack of harmonious muscle recruitment/derecruitment may play a role in pain transition. Motor behavior changed in shoulder pain conditions underlining that motor variability may play a role in the WMSD development as corroborated by the changes in kinematics variability seen with discomfort. This prognostic hypothesis was further, supported by the increased motor variability among workers with high experience. Conclusion:, Quantitative assessments of the functional motor adaptations can be a way to benchmark the pain status and help to indentify signs indicating WMSD development. Motor variability is an important characteristic in ergonomic situations. Future studies will investigate the potential benefit of inducing motor variability in occupational settings. [source] Interactions between arbuscular mycorrhizal fungi and bacteria and their potential for stimulating plant growthENVIRONMENTAL MICROBIOLOGY, Issue 1 2006Veronica Artursson Summary Arbuscular mycorrhizal (AM) fungi and bacteria can interact synergistically to stimulate plant growth through a range of mechanisms that include improved nutrient acquisition and inhibition of fungal plant pathogens. These interactions may be of crucial importance within sustainable, low-input agricultural cropping systems that rely on biological processes rather than agrochemicals to maintain soil fertility and plant health. Although there are many studies concerning interactions between AM fungi and bacteria, the underlying mechanisms behind these associations are in general not very well understood, and their functional properties still require further experimental confirmation. Future mycorrhizal research should therefore strive towards an improved understanding of the functional mechanisms behind such microbial interactions, so that optimized combinations of microorganisms can be applied as effective inoculants within sustainable crop production systems. In this context, the present article seeks to review and discuss the current knowledge concerning interactions between AM fungi and plant growth-promoting rhizobacteria, the physical interactions between AM fungi and bacteria, enhancement of phosphorus and nitrogen bioavailability through such interactions, and finally the associations between AM fungi and their bacterial endosymbionts. Overall, this review summarizes what is known to date within the present field, and attempts to identify promising lines of future research. [source] Characterization of CD4+ T-cell,dendritic cell interactions during secondary antigen exposure in tolerance and primingIMMUNOLOGY, Issue 4 2009Catherine M. Rush Summary Despite the recent advances in our understanding of the dynamics of the cellular interactions associated with the induction of immune responses, comparatively little is known about the in vivo behaviour of antigen-experienced T cells upon secondary antigen exposure in either priming or tolerance. Such information would provide an insight into the functional mechanisms employed by memory T cells of distinct phenotypes and provide invaluable knowledge of how a specific tolerogenic or immunogenic state is maintained. Using real-time imaging to follow the in vivo motility of naïve, primed and tolerized CD4+ T cells and their interactions with dendritic cells (DCs), we demonstrate that each of these distinct functional phenotypes is associated with specific patterns of behaviour. We show that antigen-experienced CD4+ T cells, whether primed or tolerized, display inherently slower migration, making many short contacts with DCs in the absence of antigen. Following secondary exposure to antigen, primed T cells increase their intensity or area of interaction with DCs whereas contacts between DCs and tolerized T cells are reduced. Importantly, this was not associated with alterations in the contact time between DCs and T cells, suggesting that T cells that have previously encountered antigen are more effective at surveying DCs. Thus, our studies are the first to demonstrate that naïve, primed and tolerized T cells show distinct behaviours before and after secondary antigen-encounter, providing a novel mechanism for the increased immune surveillance associated with memory T cells. These findings have important consequences for many immunotherapeutics, which aim to manipulate secondary immune responses. [source] Alteration and role of heat shock proteins in acute pancreatitisJOURNAL OF DIGESTIVE DISEASES, Issue 5 2010Jia Yan FENG Many etiological factors are involved in the pathogenesis of acute pancreatitis. The pathogenesis of acute pancreatitis has been attributed to such causes as trypsin autodigestion, pancreatic microcirculation malfunction, the calcium overload in pancreatic acinar cells, oxygen free radical injury, cytokine injury, and has been treated in detail in numerous reviews. More recently, heat shock proteins (HSP), particularly heat shock protein 60 (HSP60), have receive increasing attention as another possible factor in the pathogenesis and development of acute pancreatitis. This brief review aims to: (i) outline our current understanding of HSP and their role in pancreatitis; (ii) discuss the available evidences that suggest HSP's interplay between pancreas tissues and etiological agents; (iii) delineate the functional mechanisms of HSP proposed by different research groups, and offer new thinking in preventing and treating acute pancreatitis in general. [source] Exploring functional roles of multibinding protein interfacesPROTEIN SCIENCE, Issue 8 2009Manoj Tyagi Abstract Cellular processes are highly interconnected and many proteins are shared in different pathways. Some of these shared proteins or protein families may interact with diverse partners using the same interface regions; such multibinding proteins are the subject of our study. The main goal of our study is to attempt to decipher the mechanisms of specific molecular recognition of multiple diverse partners by promiscuous protein regions. To address this, we attempt to analyze the physicochemical properties of multibinding interfaces and highlight the major mechanisms of functional switches realized through multibinding. We find that only 5% of protein families in the structure database have multibinding interfaces, and multibinding interfaces do not show any higher sequence conservation compared with the background interface sites. We highlight several important functional mechanisms utilized by multibinding families. (a) Overlap between different functional pathways can be prevented by the switches involving nearby residues of the same interfacial region. (b) Interfaces can be reused in pathways where the substrate should be passed from one protein to another sequentially. (c) The same protein family can develop different specificities toward different binding partners reusing the same interface; and finally, (d) inhibitors can attach to substrate binding sites as substrate mimicry and thereby prevent substrate binding. [source] | ||||||||||||||||