• Journal of Microbiology and Biotechnology
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• 제26권11호
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• pp.1845-1854
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• 2016

The transglycosylation activity of amylosucrase (ASase) has received significant attention owing to its use of an inexpensive donor, sucrose, and broad acceptor specificity, including glycone and aglycone compounds. The transglycosylation reaction of recombinant ASase from Deinococcus radiopugnans (DRpAS) was investigated using various phenolic compounds, and quercetin-3-O-rutinoside (rutin) was found to be the most suitable acceptor molecule used by DRpAS. Two amino acid residues in DRpAS variants (DRpAS Q299K and DRpAS Q299R), assumed to be involved in acceptor binding, were constructed by site-directed mutagenesis. Intriguingly, DRpAS Q299K and DRpAS Q299R produced 10-fold and 4-fold higher levels of rutin transglycosylation product than did the wild-type (WT) DRpAS, respectively. According to in silico molecular docking analysis, the lysine residue at position 299 in the mutants enables rutin to more easily position inside the active pocket of the mutant enzyme than in that of the WT, due to conformational changes in loop 4.

• 미생물학회지
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• 제35권2호
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• pp.146-152
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• 1999

충치 원인균의 일종인 Streptococcus sobrinus ATCC27351 균주를 자외선 조사와 NTG 처리에 의하여 bacitracin 내성변이주를 얻었다. 선발된 변이주들 중 glucosyltransferase 활성이 모균주보다 증가된 변이주 4균주를 선발하였다. 이들의 bacitracin 내성은 모균주 보다 5~48배, glucosyltransferase 활성은 약 2배 증가하였다. 모균주의 glucosyltransferase를 이용하여 maltose acceptor 반응을 하여 \ulcorner 와 image analysis 로 분석하였다. 그 결과 sucrose 와 acceptor를 사용하여 반응을 시킨 결과 모균주와 변이주의 glucose 전이효소 사이에는 acceptor 특이성에 차이가 있었다. 모균주의 효소와는 반응하지 않는 acceptor 인 fructose를 함유하는 1-kestose와 nystose 그리고 turanose를 acceptor 로 하여 변이주 S. sobrinus BR24C 균주의 glucosyltransferase와 반응을 시켰다. 얻어진 acceptor 산물을 정제하여 \sup 1\H, \sup 13\C-NMR 분석을 한 결과, 자연계에서는 발견되지 않는 새로운 구조의 올리고당 \6^{3}$-$\alpha$-D-glucopyranosyl \3^{2}$-O-$\alpha$-D-glucopyranosyl-D-fructose와 \6^{4}$-$\alpha$-D-glucopyranosyl \1^{3}$-$\beta$-D-fructofuranosyl sucrose을 확인하였다.

• Journal of Microbiology and Biotechnology
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• 제15권1호
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• pp.99-104
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• 2005

Microbacterium laevaniformans levansucrase synthesized various hetero-oligosaccharides by transferring fructosyl residue from sucrose to various saccharides as acceptors. The acceptor specificity test showed that reducing saccharides were more favorable acceptors than nonreducing saccharides. The transfructosylated product, fructosyl galactose, was produced in the presence of D-galactose as an acceptor. The chemical structure of the resulting fructosyl galactose was analyzed by yeast invertase and NMR, and identified as O-$\alpha$-D-galactosyl-(1${\to}$2)-$\beta$-D-fructofuranoside. These results indicate that the main transfructosylation activity of the enzyme is to make nonreducing transferred products via a transfer of fructosyl residue to acceptor molecules having reducing group. When nonreducing sugars, such as methyl $\alpha$-D-glucoside and methyl $\alpha$-D-galactoside, were used as an acceptor, the transfer product was also formed in spite of the reducing group blocked with methyl group. The fact that no transfer product was formed with sugar alcohols as acceptors was suggested to be due to marked conformational difference of acceptors.

• Bulletin of the Korean Chemical Society
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• 제18권1호
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• pp.18-23
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• 1997

Data from structure/activity studies in vir gene induction system have led to evaluate the working hypothesis of interaction between phenolic inducers and phenol binding proteins. The primary specificity in the association of a phenolic inducer with its receptor in our system is hypothesized to be the hydrogen bonding interactions through the ortho methoxy substituents as well as the proton transfer between the inducer and the binding protein. In this paper the proposed working model for phenol-mediating signal transduction was evaluated in several ways. The importance of the general acid-base catalysis was first addressed by the presence of an acidic residue and a basic residue in the phenol binding protein. Series of compounds were tested for vir gene expression activity to confirm the generation of a strong nucleophile by an acidic residue and an involvement of a basic residue as a proton acceptor. An attempt was made to correlate the pKa values of the phenolic compounds with vir gene induction activities as inducers to further support the proposed proton transfer mechanism. Finally, it was also observed that the regioselectively attached methoxy group on phenol compounds is required as the proper hydrogen bond acceptor.

• 한국생물물리학회:학술대회논문집
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• 한국생물물리학회 1997년도 학술발표회
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• pp.37-37
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• 1997

The catalytic efficiency of pyranose oxidase (EC 1.1.3.10.) determined for various sugars showed that D-glucose is the preferred substrate and the enzyme oxidized the various aldonolactones. The specificity constants of pyranose oxidase determined for deoxy- and deoxyfluoro-D-glucoses showed that a hydroxy group at C-4 of D-glucose acts as a hydrogen-bone acceptor, at C-6 as a hydrogen-bond donor, and at C-1 as a hydrogen-bond donor.(omitted)

• Applied Biological Chemistry
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• 제21권2호
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• pp.112-118
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• 1978

소의 갑상선에서 추출한 Xanthine oxidase를 disc gel eleectrophoresis로서 정제도(Purity)를 측정하여 Xanthine oxidase 이외의 다른 불순 단백질이 나타나지 않을 때까지 정제하였다. 그 정제 과정은 Pancreatin digestion, butanol 추출, ammonium sulfate 단백질 침전, calcium phosphate gel-cellulose column chromatography, gel filtration, preparative Sephadex G-25 column electrophoresis와 Preparative polyacrylamide gel electrophoresis 등을 포함하고 있다. 이러한 과정을 통하여 갑상선 Xanthine oxidase는 1,000배 정도 정제되었다. 그러나 효소의 비활성도(Specific activity)는 우유에서 추출한 이 효소에 상응하는 정도로 정제된 효소의 비활성도와 비교 되었을 때 지극히 낮았다. 갑상선 Xanthine oxidase도 효소 반응에 필요한 기질과 electron acceptor의 특수성(Specificity)이 어느 특수한 한 기질에 한정되지 않았음을 보였고 Kinetic 성질도 우유에서 추출된 Xanthine oxidase와 비교하였을 때 가장 일반적인 Xanthine oxidase 기질에 대한 Michaelis 상수(Km)가 약간의 예외도 있었으나 상당히 비슷하였다.

• Journal of Microbiology and Biotechnology
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• 제29권2호
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• pp.268-273
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• 2019

The specificity of a Bacillus licheniformis uridine diphosphate (UDP) glycosyltransferase, YjiC, was increased towards thymidine diphosphate (TDP)-sugar by site-directed mutagenesis. The Arg-282 of YjiC was identified and investigated by substituting with Trp. Conversion rate and kinetic parameters were compared between YjiC and its variants with several acceptor substrates such as 7-hydroxyflavone (7-HF), 4',7-dihydroxyisoflavone, 7,8-dihydroxyflavone and curcumin. Molecular docking of TDP-glucose and 7-HF with YjiC model showed pi-alkyl interaction with Arg-282 and His-14, and pi-pi interaction with $His^{14}$ and thymine ring. YjiC (H14A) variant lost its glucosylation activity with TDP-glucose validating significance of His-14 in binding of TDP-sugars.

• Journal of Microbiology and Biotechnology
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• 제30권9호
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• pp.1436-1442
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• 2020

Amylosucrase (ASase, E.C. 2.4.1.4) is capable of efficient glucose transfer from sucrose, acting as the sole donor molecule, to various functional acceptor compounds, such as polyphenols and flavonoids. An ASase variant from Deinococcus geothermalis, in which the 226^th alanine is replaced with asparagine (DgAS-A226N), shows increased polymerization activity due to changes in the flexibility of the loop near the active site. In this study, we further investigated how the mutation modulates the enzymatic activity of DgAS using molecular dynamics and docking simulations to evaluate interactions between the enzyme and phenolic compounds. The computational analysis revealed that the A226N mutation could induce and stabilize structural changes near the substrate-binding site to increase glucose transfer efficiency to phenolic compounds. Kinetic parameters of DgAS-A226N and WT DgAS were determined with sucrose and 4-methylumbelliferone (MU) as donor and acceptor molecules, respectively. The k_cat/K_m value of DgAS-A226N with MU (6.352 mM^-1min^-1) was significantly higher than that of DgAS (5.296 mM^-1min^-1). The enzymatic activity was tested with a small phenolic compound, hydroquinone, and there was a 1.4-fold increase in α-arbutin production. From the results of the study, it was concluded that DgAS-A226N has improved acceptor specificity toward small phenolic compounds by way of stabilizing the active conformation of these compounds.

• Journal of Microbiology and Biotechnology
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• 제17권3호
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• pp.454-460
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• 2007

Enzymatic properties and substrate specificity of recombinant $\beta-glycosidases$ from a hyperthermophilic archaeon, Sulfolobus shibatae (rSSG), were analyzed. rSSG showed its optimum temperature and pH at $95^{\circ}C$ and pH 5.0, respectively. Thermal inactivation of rSSG showed that its half-life of enzymatic activity at $75^{\circ}C$ was 15 h whereas it drastically decreased to 3.9 min at $95^{\circ}C$. The addition of 10 mM of $MnCl_2$ enhanced the hydrolysis activity of rSSG up to 23% whereas most metal ions did not show any considerable effect. Dithiothreitol (DTT) and 2-mercaptoethanol exhibited significant influence on the increase of the hydrolysis activity of rSSG rSSG apparently preferred laminaribiose $(\beta1\rightarrow3Glc)$, followed by sophorose $(\beta1\rightarrow2Glc)$, gentiobiose $(\beta1\rightarrow6Glc)$, and cellobiose $(\beta1\rightarrow4Glc)$. Various. intermolecular transfer products were formed by rSSG in the lactose reaction, indicating that rSSG prefers lactose as a good acceptor as well as a donor. The strong intermolecular transglycosylation activity of rSSG can be applied in making functional oligosaccharides.

• BMB Reports
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• 제35권5호
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• pp.513-517
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• 2002

We describe a new method for identifying the sequences that signal the start of translation, and the boundaries between exons and introns (donor and acceptor sites) in human mRNA. According to the mandatory keyword, ORGANISM, and feature key, CDS, a large set of standard data for each signal site was extracted from the ASCII flat file, gbpri.seq, in the GenBank release 108.0. This was used to generate the scoring matrices, which summarize the sequence information for each signal site. The scoring matrices take into account the independent nucleotide frequencies between adjacent bases in each position within the signal site regions, and the relative weight on each nucleotide in proportion to their probabilities in the known signal sites. Using a scoring scheme that is based on the nucleotide scoring matrices, the method has great sensitivity and specificity when used to locate signals in uncharacterized human genomic DNA. These matrices are especially effective at distinguishing true and false sites.