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Search Results: 1 - 10 of 18893 matches for " Saemee Song "
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Interaction Mediated by the Putative Tip Regions of MdsA and MdsC in the Formation of a Salmonella-Specific Tripartite Efflux Pump
Saemee Song, Soonhye Hwang, Seunghwa Lee, Nam-Chul Ha, Kangseok Lee
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0100881
Abstract: To survive in the presence of a wide range of toxic compounds, gram-negative bacteria expel such compounds via tripartite efflux pumps that span both the inner and outer membranes. The Salmonella-specific MdsAB pump consists of MdsB, a resistance-nodulation-division (RND)-type inner membrane transporter (IMT) that requires the membrane fusion protein (MFP) MdsA, and an outer membrane protein (OMP; MdsC or TolC) to form a tripartite efflux complex. In this study, we investigated the role of the putative tip regions of MdsA and its OMPs, MdsC and TolC, in the formation of a functional MdsAB-mediated efflux pump. Comparative analysis indicated that although sequence homologies of MdsA and MdsC with other MFPs and OMPs, respectively, are extremely low, key residues in the putative tip regions of these proteins are well conserved. Mutagenesis studies on these conserved sites demonstrated their importance for the physical and functional interactions required to form an MdsAB-mediated pump. Our studies suggest that, despite differences in the primary amino acid sequences and functions of various OMPs and MFPs, interactions mediated by the conserved tip regions of OMP and MFP are required for the formation of functional tripartite efflux pumps in gram-negative bacteria.
Membrane Fusion Proteins of Type I Secretion System and Tripartite Efflux Pumps Share a Binding Motif for TolC in Gram-Negative Bacteria
Minho Lee, So-Young Jun, Bo-Young Yoon, Saemee Song, Kangseok Lee, Nam-Chul Ha
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0040460
Abstract: The Hly translocator complex of Escherichia coli catalyzes type I secretion of the toxin hemolysin A (HlyA). In this complex, HlyB is an inner membrane ABC (ATP Binding Cassette)-type transporter, TolC is an outer membrane channel protein, and HlyD is a periplasmic adaptor anchored in the inner membrane that bridges HlyB to TolC. This tripartite organization is reminiscent of that of drug efflux systems such as AcrA-AcrB-TolC and MacA-MacB-TolC of E. coli. We have previously shown the crucial role of conserved residues located at the hairpin tip region of AcrA and MacA adaptors during assembly of their cognate systems. In this study, we investigated the role of the putative tip region of HlyD using HlyD mutants with single amino acid substitutions at the conserved positions. In vivo and in vitro data show that all mutations abolished HlyD binding to TolC and resulted in the absence of HlyA secretion. Together, our results suggest that, similarly to AcrA and MacA, HlyD interacts with TolC in a tip-to-tip manner. A general model in which these conserved interactions induce opening of TolC during drug efflux and type I secretion is discussed.
Modulation of RNase E Activity by Alternative RNA Binding Sites
Daeyoung Kim, Saemee Song, Minho Lee, Hayoung Go, Eunkyoung Shin, Ji-Hyun Yeom, Nam-Chul Ha, Kangseok Lee, Yong-Hak Kim
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0090610
Abstract: Endoribonuclease E (RNase E) affects the composition and balance of the RNA population in Escherichia coli via degradation and processing of RNAs. In this study, we investigated the regulatory effects of an RNA binding site between amino acid residues 25 and 36 (24LYDLDIESPGHEQK37) of RNase E. Tandem mass spectrometry analysis of the N-terminal catalytic domain of RNase E (N-Rne) that was UV crosslinked with a 5′-32P-end-labeled, 13-nt oligoribonucleotide (p-BR13) containing the RNase E cleavage site of RNA I revealed that two amino acid residues, Y25 and Q36, were bound to the cytosine and adenine of BR13, respectively. Based on these results, the Y25A N-Rne mutant was constructed, and was found to be hypoactive in comparison to wild-type and hyperactive Q36R mutant proteins. Mass spectrometry analysis showed that Y25A and Q36R mutations abolished the RNA binding to the uncompetitive inhibition site of RNase E. The Y25A mutation increased the RNA binding to the multimer formation interface between amino acid residues 427 and 433 (427LIEEEALK433), whereas the Q36R mutation enhanced the RNA binding to the catalytic site of the enzyme (65HGFLPL*K71). Electrophoretic mobility shift assays showed that the stable RNA-protein complex formation was positively correlated with the extent of RNA binding to the catalytic site and ribonucleolytic activity of the N-Rne proteins. These mutations exerted similar effects on the ribonucleolytic activity of the full-length RNase E in vivo. Our findings indicate that RNase E has two alternative RNA binding sites for modulating RNA binding to the catalytic site and the formation of a functional catalytic unit.
A review of developments of EEG-based automatic medical support systems for epilepsy diagnosis and seizure detection  [PDF]
Yuedong Song
Journal of Biomedical Science and Engineering (JBiSE) , 2011, DOI: 10.4236/jbise.2011.412097
Abstract: Epilepsy is one of the most common neurological disorders-approximately one in every 100 people worldwide are suffering from it. The electroencephalogram (EEG) is the most common source of information used to monitor, diagnose and manage neurological disorders related to epilepsy. Large amounts of data are produced by EEG monitoring devices, and analysis by visual inspection of long recordings of EEG in order to find traces of epilepsy is not routinely possible. Therefore, automated detection of epilepsy has been a goal of many researchers for a long time. Until now, reviews of epileptic seizure detection have been published but none of them has specifically reviewed developments of automatic medical support systems utilized for EEG-based epileptic seizure detection. This review aims at filling this lack. The main objective of this review will be to briefly discuss different methods used in this research field and describe their critical properties.
Average Power Function of Noise and Its Applications in Seasonal Time Series Modeling and Forecasting  [PDF]
Qiang Song
American Journal of Operations Research (AJOR) , 2011, DOI: 10.4236/ajor.2011.14034
Abstract: This paper presents a new method of detecting multi-periodicities in a seasonal time series. Conventional methods such as the average power spectrum or the autocorrelation function plot have been used in detecting multiple periodicities. However, there are numerous cases where those methods either fail, or lead to incorrectly detected periods. This, in turn in applications, produces improper models and results in larger forecasting errors. There is a strong need for a new approach to detecting multi-periodicities. This paper tends to fill this gap by proposing a new method which relies on a mathematical instrument, called the Average Power Function of Noise (APFN) of a time series. APFN has a prominent property that it has a strict local minimum at each period of the time series. This characteristic helps one in detecting periods in time series. Unlike the power spectrum method where it is assumed that the time series is composed of sinusoidal functions of different frequencies, in APFN it is assumed that the time series is periodic, the unique and a much weaker assumption. Therefore, this new instrument is expected to be more powerful in multi-periodicity detection than both the autocorrelation function plot and the average power spectrum. Properties of APFN and applications of the new method in periodicity detection and in forecasting are presented.
Green Oil Production by Hydroprocessing  [PDF]
Song Chen
International Journal of Clean Coal and Energy (IJCCE) , 2012, DOI: 10.4236/ijcce.2012.14005
Abstract: Owning to GHG emissions control and prospective future of biofuel, it is encouraged to look for a shift to alternate industrial feedstock and green processes to produce these chemicals from renewable biomass resources. Besides hydrotreating bio-oil or crop oil to produce second generation bio-fuels, the bio-oil can be co-processed in various refining units and it also may lead to the production of green diesel, which is not only an opportunity but also a challenge for petroleum industry. Green oil or green diesel can be produced by co-processing renewable diesel with petroleum oil in present hydroprocressing unit. Many researches and works have been done on co-processing process and related catalyst in the hope of figuring out the mechanism and optimizing the co-processing technology with adding amounts vegetable oils or animal fats to the traditional petroleum refining process to produce green oil. This is a literature review about green oil production by hydroprocessing and co-processing.
Credit Rating in China’s Bond Market: Evidence from Short-Term Financing Bonds  [PDF]
Song Zhu
Modern Economy (ME) , 2013, DOI: 10.4236/me.2013.42015

In recent years, the Chinese government has highly emphasized the development of bond market, which plays an important role during the development of macro-economy and finance sector in China, especially on some crucial steps concerning national economy and the peoples livelihood, as well as reforms in banking industry and the financial innovations. However, the bond market is smaller compared with its counterparts abroad, and its structure is much simpler. To promote the development of bond market, credit rating is very important, which has been hotly discussed during and after the recent financial crisis. This paper discusses the credit rating of bond in China, particularly the short-term financing bonds (STFBs). Our results reveal that almost all credit ratings for STFBs are A-1, the highest rating, which cannot provide investors with effective information, thus being consistent with some critical voices. However, the credit ratings for issuing firms exhibit significant difference so that they are reliable benchmarks for bond investors, and credit ratings indeed reflect the risk of issuing firms in China. Our paper provides more information for foreign and domestic investors about the bond market and the credit rating in China, and gives answer to the question about efficiency of bond rating in China. We provide some evidence for the reliability of rating in China though it is still in its early stage.

Age Distribution of a Zero-Growth Population: Implications for China  [PDF]
Song Jian
Chinese Studies (ChnStd) , 2013, DOI: 10.4236/chnstd.2013.22011
Abstract: It is generally accepted that zero-growth population would be the long-term destiny of any population. China’s population is expected to reach 1.4 billion with zero-growth around 2030, if the low fertility policy continues up to then. Demographic dynamics indicate that the age composition of a steady zero-growth society would asymptotically approach the population mix of today’s many developed countries. Here we present a brief analysis and some insights into the age composition of a zero-growth society and the connectedness between total fertility rate, net reproduction rate and replacement level of fertility. Other formulas useful for demographic studies are also provided to further the analysis. Our results reveal that the age composition of China’s population in 2050 would be similar to those of some developed countries today. We argue that the misgivings about “population aging” or the fear of a “winter of humanity” in China stem from rather oversimplified estimations.
Thoughts on Accelerating the Development of China’s Service Trade Issues  [PDF]
Xingang Song
Open Journal of Social Sciences (JSS) , 2014, DOI: 10.4236/jss.2014.29034

With the globalization of the world economy and the integration of development, trade in services has become an important driving force and source of the current international economic and trade growth. Since joining WTO in 2001, China’s service trade opening steadily expanded, the status of service trade in the foreign trade of the gradual increase in the Chinese. Although China’s service trade has a rapid development, from an overall point of view, the development still remain relatively backward with low level of opening. What’s more, compared with the world service trade power, there is a very big disparity between them. This paper expounds the present situation of the development of service trade in China, analyzes the existing problems, and puts forward some countermeasures and suggestions to promote China’s service trade development.

Analysis of a Methanol-Power Polygeneration System from Natural Gas  [PDF]
Xiaona Song
Journal of Power and Energy Engineering (JPEE) , 2014, DOI: 10.4236/jpee.2014.24010
Abstract: This paper analyzes the characteristics of a Natural Gas (NG)-based Methanol-Power Polygeneration System (MPPS). The structures and parameters of the polygeneration systems are investigated to explore the appropriate process for each polygeneration system. And some effective methods, such as exergy distribution analysis and energy-utilization diagrams (EUD) are adopted to investigate the performance & characteristic of the system. The results reveal that, MPPS adopted Partial Reforming and Partial Cycling synthesis (PR/PC) process can reach good performance, while MPPS exhibits poor performance when adopting Full Reforming and Once Through synthesis (FR/OT) process. Through further study with exergy analysis method, we find that the particular synthesis and separation properties of methanol lead to such difference. Therefore, the characteristics of chemical product should be important factors in the configuration and integration of polygeneration systems. The work of this paper is significant for the research and development of polygeneration system.
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