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Oh, Juntaek,Hwang, Ingyu,Rhee, Sangkee American Society for Biochemistry and Molecular Bi 2016 The Journal of biological chemistry Vol.291 No.29
<P>In Burkholderia species, the production of oxalate, an acidic molecule, is a key event for bacterial growth in the stationary phase. Oxalate plays a central role in maintaining environmental pH, which counteracts inevitable population-collapsing alkaline toxicity in amino acid-based culture medium. In the phytopathogen Burkholderia glurnae, two enzymes are responsible for oxalate production. First, the enzyme oxalate biosynthetic component A (ObcA) catalyzes the formation of a tetrahedral C6-CoA adduct from the substrates acetyl-CoA and oxaloacetate. Then the ObcB enzyme liberates three products from the C6-CoA adduct: oxalate, acetoacetate, and CoA. Interestingly, these two stepwise reactions are catalyzed by a single bifunctional enzyme, Obc1, from Burkholderia thailandensis and Burkholderia pseudornallei. Obc1 has an ObcA-like N-terminal domain and shows ObcB activity in its C-terminal domain despite no sequence homology with ObcB. We report the crystal structure of Obcl in its apo and glycerol-bound form at 2.5 A and 2.8 A resolution, respectively. The Obcl N-terminal domain is essentially identical both in structure and function to that of ObcA. Its C-terminal domain has an alpha/beta hydrolase fold that has a catalytic triad for oxalate production and a novel oxyanion hole distinct from the canonical HGGG motif in other a/0 hydrolases. Functional analyses through mutagenesis studies suggested that His -934 is an additional catalytic acid/base for its lyase activity and liberates two additional products, acetoacetate and CoA. These results provide structural and functional insights into bacterial oxalogenesis and an example of divergent evolution of the a/13 hydrolase fold, which has both hydrolase and lyase activity.</P>
Highly efficient W-band 2.5 GHz bandwidth pulse generator with −1 dBm output power in 65 nm CMOS
Juntaek Oh,Jingyu Jang,Songcheol Hong IET 2016 Electronics letters Vol.52 No.3
<P>A W-band 2.5 GHz bandwidth pulse generator comprising a voltage-controlled oscillator (VCO) and a novel pulse former in a 65 nm CMOS technology is presented. The proposed sub-harmonic pumped pulse former, which plays roles as both a frequency doubler and a pulse former, is designed to obtain high efficiency using a transformer-based current reuse circuit. The VCO is implemented with a parallel combining transformer, which makes it insensitive to load variations due to pulse formation. Measurements show that the pulse generator achieves -1 dBm peak output power at 79 GHz. It can generate 800 ps pulse signals with an RF carrier of 76.1-79.6 GHz, achieving the energy cost rate of 50 pJ/pulse with a 1.25 GHz pulse repetition period.</P>
Diatom Allantoin Synthase Provides Structural Insights into Natural Fusion Protein Therapeutics
Oh, Juntaek,Liuzzi, Anastasia,Ronda, Luca,Marchetti, Marialaura,Corsini, Romina,Folli, Claudia,Bettati, Stefano,Rhee, Sangkee,Percudani, Riccardo American Chemical Society 2018 ACS CHEMICAL BIOLOGY Vol.13 No.8
<P>Humans have lost the ability to convert urate into the more soluble allantoin with the evolutionary inactivation of three enzymes of the uricolytic pathway. Restoration of this function through enzyme replacement therapy can treat severe hyperuricemia and Lesch-Nyhan disease. Through a genomic exploration of natural gene fusions, we found that plants and diatoms independently evolved a fusion protein (allantoin synthase) complementing two human pseudogenes. The 1.85-Å-resolution crystal structure of allantoin synthase from the diatom <I>Phaeodactylum tricornutum</I> provides a rationale for the domain combinations observed in the metabolic pathway, suggesting that quaternary structure is key to the evolutionary success of protein domain fusions. Polyethylene glycol (PEG) conjugation experiments indicate that a PEG-modified form of the natural fusion protein provides advantages over separate enzymes in terms of activity maintenance and manufacturing of the bioconjugate. These results suggest that the combination of different activities in a single molecular unit can simplify the production and chemical modification of recombinant proteins for multifunctional enzyme therapy.</P> [FIG OMISSION]</BR>
A W-Band High-Efficiency CMOS Differential Current-Reused Frequency Doubler
Juntaek Oh,Jingyu Jang,Choul-Young Kim,Songcheol Hong THE INSTITUTE OF ELECTRICAL ENGINEERS 2015 IEEE Microwave and Wireless Components Letters Vol. No.
<P>A W-band differential frequency doubler using a current-reuse configuration in a 65 nm CMOS process is presented in this letter. The differential current-reuse circuit with a second harmonic coupling transformer is introduced to improve conversion gain at small input powers minimizing the effect of the RF bypass capacitor. The proposed circuit achieves a conversion gain of 0.8 ~ -4.2 dB and a fundamental rejection above 19 dB in the input frequency range of 36.5~44 GHz with -4 dBm input power. It has conversion gain variation below 1 dB when the input power varies from -7.4 to 0.1 dBm at 77 GHz. The dc power consumption is 14 mW. It has the highest conversion gain with the smallest chip size of 0.22 mm<SUP>2</SUP> among all V-/W-band CMOS frequency doublers.</P>
Structural Basis for Bacterial Quorum Sensing-mediated Oxalogenesis
Oh, Juntaek,Goo, Eunhye,Hwang, Ingyu,Rhee, Sangkee American Society for Biochemistry and Molecular Bi 2014 The Journal of biological chemistry Vol.289 No.16
<P>The <I>Burkholderia</I> species utilize acetyl-CoA and oxaloacetate, substrates for citrate synthase in the TCA cycle, to produce oxalic acid in response to bacterial cell to cell communication, called quorum sensing. Quorum sensing-mediated oxalogenesis via a sequential reaction by ObcA and ObcB counteracts the population-collapsing alkaline pH of the stationary growth phase. Thus, the oxalic acid produced plays an essential role as an excreted public good for survival of the group. Here, we report structural and functional analyses of ObcA, revealing mechanistic features distinct from those of citrate synthase. ObcA exhibits a unique fold, in which a (β/α)<SUB>8</SUB>-barrel fold is located in the C-domain with the N-domain inserted into a loop following α1 in the barrel fold. Structural analyses of the complexes with oxaloacetate and with a bisubstrate adduct indicate that each of the oxaloacetate and acetyl-CoA substrates is bound to an independent site near the metal coordination shell in the barrel fold. In catalysis, oxaloacetate serves as a nucleophile by forming an enolate intermediate mediated by Tyr<SUP>322</SUP> as a general base, which then attacks the thioester carbonyl carbon of acetyl-CoA to yield a tetrahedral adduct between the two substrates. Therefore, ObcA catalyzes its reaction by combining the enolase and acetyltransferase superfamilies, but the presence of the metal coordination shell and the absence of general acid(s) produces an unusual tetrahedral CoA adduct as a stable product. These results provide the structural basis for understanding the first step in oxalogenesis and constitute an example of the functional diversity of an enzyme for survival and adaptation in the environment.</P>
5-㎒ Pseudo-differential Current-mode CMOS Relaxation VCO with Temperature Stability of 41.8 ppm/℃
Juntaek Oh,Jong-Ryul Yang 대한전자공학회 2019 Journal of semiconductor technology and science Vol.19 No.6
This letter presents a pseudo-differential current-mode relaxation voltage-controlled oscillator for small form factor applications. A pseudodifferential current-mode comparator with a temperature compensated RC circuit was composed both to obtain half duty cycle and have a constant charge and discharge time with temperature change. A current source with two types of gate-oxide transistor combinations was able to obtain the reference voltage and had an ultra-low temperature coefficient, thus mitigating frequency variation with regard to temperature. The proposed voltage-controlled oscillator was implemented in a low power 65-㎚ CMOS process and occupied 0.011 ㎟. Measurements showed that the voltage-controlled oscillator operated at 4.75-5.09 ㎒ with a supply voltage of 1.0 V, and its DC power consumption was 40 ㎼ including a 3-stage buffer. A low frequency variation of 41.8 ppm/℃ was achieved for the temperature range of 20 to 100 ℃.
한글 자소의 획 정보에 의한 멀티미디어 단말기에서의 온라인 한글 문자 인식
오준택,정모문,이우범,김욱현,Oh Juntaek,Jung Momoon,Lee Woobeom,Kim Wookhyun 한국융합신호처리학회 2000 융합신호처리학회 논문지 (JISPS) Vol.1 No.1
The Korean character recognition technology for user interface in multimedia terminal requires fast processing time and high recognition rate. In this paper, we propose an phoneme and character recognition technology which uses characteristic information of korean and features of input strokes, i.e, feature point, feature vector, virtual vector, position relation between strokes. And, a recognition both phoneme and character by the various writing types of users uses korean database. The Korean database has been constructed by the characteristic information of korean and phoneme models which have various stroke information. Also, we use successive processing by the position relation between strokes and backtracking processing by the modification processing of stroke numbers which composed of each phoneme. This method reduces the complex processing of phoneme separation. The proposed on-line korean character recognition system has obtained 13msec average character processing time and correct recognition rate more than $95{\%}$ In a recognition experiment, where we tested 600 characters written by 10 people among 1,200 words.