• BMB Reports
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• 제28권4호
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• pp.363-367
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• 1995

E. coli methionyl-tRNA synthetase is one of the class I tRNA synthetases. The Tryptophane residue at the position 461 located in the C-terminal domain of the enzyme is a key amino acid for the interaction with the anticodon of $tRNA^{Met}$. W461 was replaced with other amino acids to determine the chemical requirement for the interaction with the anticodon of $tRNA^{Met}$. Saturation mutagenesis at the position 461 generated a total of 12 substitution mutants of methionyl-tRNA synthetase. All the mutants showed the same in vivo stability as the wild-type enzyme, suggesting that the amino acid substitutions did not cause severe conformational change of the protein The mutants containing tyrosine, phenylalanine, histidine and cysteine substitutions showed in vivo activity while all the other mutants did not. The comparison of the in vitro aminoacylation activities of these mutants showed that aromatic ring structure, Van der Waals volume and hydrogen bond potential of the amino acid residue at the position 461 are the major determinants for the interaction with the anticodon of $tRNA^{Met}$.

• Journal of Microbiology and Biotechnology
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• 제18권8호
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• pp.1401-1407
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• 2008

The roles of conserved amino acid residues (Va1329-Ala330-Asn331-Glu332), constituting an extra sugar-binding space (ESBS) of Thermus maltogenic amylase (ThMA), were investigated by combinatorial saturation mutagenesis. Various ThMA mutants were firstly screened on the basis of starch hydrolyzing activity and their enzymatic properties were characterized in detail. Most of the ThMA variants showed remarkable decreases in their hydrolyzing activity, but their specificity against various substrates could be altered by mutagenesis. Unexpectedly, mutant H-16 (Gly-Leu-Val-Tyr) showed almost identical hydrolyzing and transglycosylation activities to wild type, whereas K-33 (Ser-Gly-Asp-Glu) showed an extremely low transglycosylation activity. Interestingly, K-33 produced glucose, maltose, and acarviosine from acarbose, whereas ThMA hydrolyzed acarbose to only glucose and acarviosine-glucose. These results propose that the substrate specificity, hydrolysis pattern, and transglycosylation activity of ThMA can be modulated by combinatorial mutations near the ESBS.

• Journal of Microbiology
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• 제37권3호
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• pp.154-158
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• 1999

The arginine residue at position 243 (Arg 243) of the yeast transcription factor, Gcn4p, is invariably conserved among bZIP transcription factors. Using site-directed oligonucleotide saturation mutagenesis involving two-step polymerase chain reaction (PCR) amplification, random mutations were successfully introduced at the codon of 243 in the basic domain of Gcn4p. This mutant library was transformed ito Gcn4p defective yeast strain and selected for the transcriptionally active colonies. All colonies which were transcriptionally active had arginines in the codon 243. In this study, the strand preference by Taq polymerase during mutagenesis was also tested. Oligonucleotides were specially designed to test whether or not the polymerase was preferred using the strand as a template. A population of randomly mutated products were cloned into an appropriate vector and characterized by DNA sequencing analysis. Saturation mutagenesis which was performed efficiently by this method revealed a strong bias in terms of strand preference of Taq polymerase by an approximate ratio of 3 to 1 in this study.

• Journal of Microbiology and Biotechnology
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• 제9권1호
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• pp.122-125
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• 1999

Gcn4p, a transcriptional activator protein of the yeast, Sacchromyces cerevisiae, binds to the specific sequence in the promoters of many amino acid biosynthetic genes for general control. The serine residue (Ser 242) of Gcn4p directly contacts the DNA. Here, for inspecting the DNA binding properties and the level of transcriptional activation of Gcn4p, we introduced a polymerase chain reaction (PCR) site-directed saturation mutation library into the Ser 242 site using 2 outside primers and 2 oligonucleotides with its codons fully degenerated. The sequencing analysis of 146 samples revealed the even nucleotide distribution within the experimental error showing 23, 26, 25, and 26％ frequency of U, C, A, and G bases, respectively. This method turned out to be a simple, fast, and economical method for constructing a library of all 20 amino acids at specific codon.

• 한국식품과학회지
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• 제42권2호
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• pp.198-203
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• 2010

보리 맥아에는 2종의 $\alpha$-amylase isozyme(AMY1, AMY2)이 존재하며, 이들 효소는 80% 이상의 높은 아미노산 서열 상동성을 보이지만, calcium 의존성 등 효소의 작용특성은 서로 매우 다르다. 따라서 본 연구에서는 AMY2의 활성부위 중 2번째 $\beta\rightarrow\alpha$ loop에 존재하는 42번째 alanine 잔기를 saturation mutagenesis를 이용하여 다양한 아미노산으로 치환하고, 전분 분해활성이 증가한 돌연변이를 선발하였다. 결과적으로 alanine이 proline으로 치환된 AMY2-A42P의 경우에서만 발현도가 2배 증가하는 것을 확인하였으며, 특히 정제 과정에서의 회수율 또한 4배 증가하므로 향후 효소의 생산 및 활용에 유리할 것으로 판단하였다. 이 돌연변이 효소의 calcium 의존성 및 pH 안정성 등은 AMY2와 유사한 것으로 나타났으나, 각종 전분에 대한 기질특이성은 AMY1과 AMY2의 중간적인 특성으로 변화되었다. 결국 42번째 아미노산 잔기의 proline 치환에 의해 상대적으로 발현율이 높고 기질특이성이 변화된 AMY2 유사효소의 생산이 가능하였으며, 향후 이를 이용하여 분자진화기술 등 최신 효소공학적 방법론을 적용한 다양한 연구가 가능할 것으로 기대한다.

• Journal of Microbiology and Biotechnology
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• 제26권12호
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• pp.2179-2183
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• 2016

Nitrilases pose attractive alternatives to the chemical hydrolysis of nitrile compounds. The activity of bacterial nitrilases towards substrate is intimately tied to the formation of large spiral-shaped oligomers. In the nitrilase CynD (cyanide dihydratase) from Bacillus pumilus, mutations in a predicted oligomeric surface region altered its oligomerization and reduced its activity. One mutant, CynD Y70C, retained uniform oligomer formation however it was inactive, unlike all other inactive mutants throughout that region all of which significantly perturbed oligomer formation. It was hypothesized that Y70 is playing an additional role necessary for CynD activity beyond influencing oligomerization. Here, we performed saturation mutagenesis at residue 70 and demonstrated that only tyrosine or phenylalanine is permissible for CynD activity. Furthermore, we show that other residues at this position are not only inactive, but have altered or disrupted oligomer conformations. These results suggest that Y70's essential role in activity is independent of its role in the formation of the spiral oligomer.

• Experimental Neurobiology
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• 제26권5호
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• pp.241-251
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• 2017

Saturation mutagenesis was performed on a single position in the voltage-sensing domain (VSD) of a genetically encoded voltage indicator (GEVI). The VSD consists of four transmembrane helixes designated S1-S4. The V220 position located near the plasma membrane/extracellular interface had previously been shown to affect the voltage range of the optical signal. Introduction of polar amino acids at this position reduced the voltage-dependent optical signal of the GEVI. Negatively charged amino acids slightly reduced the optical signal by 33 percent while positively charge amino acids at this position reduced the optical signal by 80%. Surprisingly, the range of V220D was similar to that of V220K with shifted optical responses towards negative potentials. In contrast, the V220E mutant mirrored the responses of the V220R mutation suggesting that the length of the side chain plays in role in determining the voltage range of the GEVI. Charged mutations at the 219 position all behaved similarly slightly shifting the optical response to more negative potentials. Charged mutations to the 221 position behaved erratically suggesting interactions with the plasma membrane and/or other amino acids in the VSD. Introduction of bulky amino acids at the V220 position increased the range of the optical response to include hyperpolarizing signals. Combining The V220W mutant with the R217Q mutation resulted in a probe that reduced the depolarizing signal and enhanced the hyperpolarizing signal which may lead to GEVIs that only report neuronal inhibition.

• 미생물학회지
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• 제52권3호
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• pp.278-285
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• 2016

E. coli의 PheA 단백질은 chorismate mutase and prephenate dehydratase (CMPD) 활성을 가지며 마지막 산물인 페닐알라닌에 의하여 되먹임제어가 되는 생합성 경로의 주요 조절 효소 중의 하나이다. 그러므로, 이 PheA 단백질은 필수 아미노산 중의 하나인 페닐알라닌의 대량 생산에 이용하기 위한 단백질 공학의 타겟이 될 수 있다. 이러한 목적으로 PheA 단백질의 마지막 생산물인 페닐알라닌에 의한 되먹임저해 저항성 유전자원을 선별하였다. 이 유전자의 산물인 $PheA^{FBR}$은 118번째 류신이 페닐알라닌으로 치환되었고, 기질인 prephenate에 대한 친화도가 야생주단백질과 비교하여 약 3.5배 정도 높았다. $PheA^{FBR}$은 세포내에서 축척되어져 되먹임저해를 하는 페닐알라닌 농도에서(약1 mM와 10 mM)에서도 50%와 40%의 활성을 유지 하고 있었고, 페닐알라닌 존재하에서 기질의 결합 성향이 협동적(cooperative) 모드에서 단독적(hyperbolic) 모드로 전환되었다. 이는 기존 연구와 비교해 볼 때, 이 돌연변이 부위는 이 융합기능 효소인 PheA 단백질의 새로운 조절 부위의 존재를 암시 한다. 효소 동력학적 결과는 PheA 단백질의 되먹임저해 저항성 획득이 아미노산 돌연변이에 의한 단백질 구조의 변화 유도에 의한 것으로 생각된다. 더 나아가, 본 연구에서 선별된 돌연변이 유전자는 생물전환법을 이용한 필수아미노산 생산에 산업적으로 응용 가능성이 있다.