방선균의 일종인 Streptomyces는 자연으로부터 유래한 항생물질의 약 3분의 2와 많은 수의 생물학적으로 활성을 가지는 물질을 생산하는 균주로 알려져 있다. 게놈 시퀀스 분석결과 Streptomyces coelicolor의 경우 18개, Streptomyces avermitilis의 경우 33개의 시토크롬 P450 유전자가 존재하는 것이 밝혀졌다. 이 연구에서는 많은 시토크롬 P450 효소들 중 S. coelicolor로부터 CYP105N1, S. avermitilis로부터 CYP158A3을 순수 분리, 정제하여 이들의 기능과 구조적 특성을 분석하였다. 재조합 CYP105N1과 CYP158A3 단백질을 대장균을 이용하여 발현시켜 정제하였을 때, 단백질이 환원된 후 CO와 결합하였을 때 보이는 시토크롬 P450 특이적인 Soret peak을 각각 448 nm, 447 nm에서 나타내었다. 정제된 CYP105N1 단백질을 이용하여 에스트라디올과 시엘리백틴 유사체와 결합시켰을 때, 특이적인 type I 스펙트럼 양상을 보였으며, H2O2를 이용한 실험에서 에스트라디올을 산화시켜 에스트리올을 형성하는 것을 확인하였다. X선 회절을 이용한 결정 분석 결과, 2.9 A 해상도의 CYP105N1의 구조를 밝혔다. 활성 부위 내의 헴 구조 위쪽으로 넓은 기질이 들어올 수 있도록 열려있음을 알았고, 부피가 약 4299 A3임을 분석을 통하여 확인하였다. 이러한 결과를 통하여 활성부위까지 이어지는 넓은 입구는 펩티딜 운반단백질 (peptidyl carrier protein)과 결합한 기질이 보다 쉽게 활성부위에 접근하여 수산화반응을 하는데 유리하게 작용할 것으로 추정된다. 시엘리백틴 유사체와의 도킹 모델을 통하여 시엘리백틴 유사체의 페닐 그룹이 헴 내의 철 분자와 <4 A 범위 내에 위치할 것이라 예측하였고 이러한 결과를 통하여 CYP105N1이 시엘리백틴 생합성 과정 중 전구체의 페닐링에 수산화 반응을 촉매하는데 관여할 것이라 추정할 수 있다. 정제된 CYP158A3 단백질을 이용한 실험에서는 미리스틱산과 결합하였을 때 특이적인 type I 스펙트럼 양상을 보이는 것을 확인하였으나 산화적 반응은 일어나지 않음을 알 수 있었다. 플라비올린 유사체인 2-OH NQ (2?hydroxynaphthoquinone)와의 결합 스펙트럼 분석결과 특이적인 type I 스펙트럼 양상을 나타내었으며 효소 반응결과 이량체 형성을 유도하였다. CYP158A3 단백질의 구조 모델과 CP158A2의 구조를 겹쳐서 보았을 때 주요 구조가 일치함을 확인하였다. 이를 통하여 CYP158A3가 S. avermitilis 내에서 C-C 결합을 촉매하여 색소 물질의 하나인 바이플라비올린의 생합성에 관여하는 상동유전자로 존재할 것이라 추정할 수 있다. S. rapamycinicus로부터 유래된 CYP107G1과 CYP122A2를 통한 실험에서는 라파마이신, 에버롤리무스, DHA와 결합하였을 때 특이적인 type I 스펙트럼 양상을 확인하였으나 라파마이신 전구체를 이용한 산화적 반응은 주어진 실험조건에서 일어나지 않았다. X선 회절을 이용한 결정 분석 결과, 단일 CYP107G1에서 2.9 A, CYP107G1-에버롤리무스 결합 조건에서 2.5 A 해상도의 결과를 얻을 수 있었다. 실험을 통하여 분리?정제된 CYP105N1, CYP158A3, CYP107G1, CYP122A2의 생화학적 특성을 분석하였다. 이러한 연구를 통하여 Streptomyces 내에 존재하는 다양한 시토크롬 P450 효소의 생화학적 기능이나 구조적 특성과 더불어 이차대사물질 합성에서의 이들의 역할을 규명함으로써 새로운 항생물질이나 유용한 이차대사물질의 발견에 기여할 것이다.
The genus Streptomyces produces approximately two-thirds of naturally occurring antibiotics and a wide array of other biologically active molecules. The genome sequence of S. coelicolor contains 18 cytochrome P450 (P450, CYP) enzymes, and S. avermitilis contains approximately 33 P450 genes. And rapamycin producing S. rapamacinicus also has several P450 genes, including CYP107G1 and CYP122A2 which are involved in the rapamycin biosynthesis. Among those various P450 enzymes, CYP105N1 from S. coelicolor, CYP158A3 from S. avermitilis and CYP107G1, CYP122A2 from S. rapamacinicus were purified and their functional and structural properties were characterized. The recombinant CYP105N1 protein has been expressed in E. coli and purified. The purified CYP105N1 protein exhibited the typical type I binding spectra with estradiol and coelibactin analogue. The oxidation of estradiol by CYP105N1, supported by H2O2, produced estriol. The crystal structure of CYP105N1 was determined at 2.9 A resolution. An unexpected wide open binding pocket located above the heme group was identified, with a volume of approximately 4299 A3. These results suggest that the large open pocket for the active site may be a key role for the peptidyl carrier protein-bound substrate which can access to the active site to perform the hydroxylation reaction. A molecular docking model with coelibactin showed that the phenyl group in coelibactin is detected within <4 A away from the heme?iron. This results suggesting that CYP105N1 may be involved in the phenyl ring hydroxylation of the precursor during coelibactin biosynthesis. CYP158A3 from S. avermitilis was heterologously expressed and purified. It exhibited the typical P450 Soret peak at 447 nm in the reduced CO bound form. Type I binding spectral changes were observed when CYP158A3 was titrated with myristic acid; however, no oxidative product was formed. An analog of flaviolin, 2 hydroxynaphthoquinone (2-OH NQ) displayed similar type I binding upon titration with purified CYP158A3. It underwent an enzymatic reaction forming dimerized products. A homology model of CYP158A3 was superimposed with the structure of CYP158A2, and the majority of structural elements aligned. These results suggest that CYP158A3 might be an orthologue of biflaviolin synthase, catalyzing C-C coupling reactions during pigment biosynthesis in S. avermitilis. CYP107G1 and CYP122A2 from S. rapamacinicus were heterologously expressed in E. coli and purified. The purified enzymes showed the typical P450 Soret peak at 448 and 446 nm, respectively, in the reduced CO bound form. Type I spectral changes were observed using rapamycin, everolimus and DHA as a ligand. However, CYP122A2 showed shifted type I spectral changes with everolimus suggest that binding moiety might be in a different manner. The crystal structure of CYP107G1 was determined at 2.9 A for a ligand free form and 2.5 A for a everolimus bound form, respectively. In conclusion, CYP105N1, CYP158A3, CYP107G1 and CYP122A2 from Streptomyces were purified and their biochemical properties were characterized. The present findings will help elucidate the functional roles of P450 enzymes and provide biochemical insights into the complicated biosynthetic pathways of secondary metabolism in Streptomyces species.
Chapter 1. Introduction 11.1. Cytochrome P450 11.1.1. History of cytochrome P450 21.1.2. Nomenclature of cytochrome P450 41.1.3. Catalytic cycle of the cytochrome P450 81.1.4. Spectroscopy of the cytochrome P450 111.1.5. Structure of the cytochrome P450 181.1.6. Diversity of P450 redox partners 221.2. Streptomyces Cytochrome P450 271.2.1. Streptomyces species 271.2.2. Cytochrome P450s in Streptomyces 271.2.3. Biological Roles of P450s in Streptomyces 281.2.4. The Structures of Streptomyces cytochrome P450s 34Chapter 2. CYP105N1 from Streptomyces coelicolor 382.1. Introduction 382.2. Materials and methods 412.2.1. Chemicals and Enzymes 412.2.2. Construction of Expression Plasmids 412.2.3. Enzymes Expression and Purification 412.2.4. Spectroscopic Characterization 422.2.5. Spectral Binding Titrations 422.2.6. Protein crystallization, data collection, and structure determination 432.2.7. CYP105N1-coelibactin complex model by molecular docking 462.2.8. P450 Enzyme Activity Assay 462.3. Results 472.3.1. Expression and purification of CYP105N1 472.3.2. Binding of coelibactin analogue and estradiol to CYP105N1 502.3.3. Catalytic activities of CYP105N1 502.3.4. Overall structure of CYP105N1 532.3.5. Wide open conformation of CYP105N1 substrate binding pocket 562.4. Discussion 62Chapter 3. CYP158A3 from Streptomyces avermitilis 673.1. Introduction 673.2. Materials and methods 693.2.1. Chemicals and enzymes 693.2.2. Construction of expression plasmids 693.2.3. Enzymes expression and purification 693.2.4. Spectroscopic characterization 703.2.5. Spectral binding titrations 703.2.6. P450 enzyme catalytic activity assay 713.2.7. Homology modeling of CYP158A3 protein 723.3. Results 733.3.1. Amino acid sequence alignments for CYP158A3 733.3.2. Expression and purification of CYP158A3 753.3.3. Binding analysis of CYP158A3 783.3.4. Catalytic activities of CYP158A3 813.4. Discussion 83Chapter 4. CYP107G1 and CYP122A2 from Streptomyces rapamycinicus 864.1. Introduction 864.2. Materials and methods 924.2.1. Chemicals and Enzymes 924.2.2. Construction of Expression Plasmids 924.2.3. Enzymes Expression and Purification 924.2.4. Spectroscopic Characterization 944.2.5. Spectral Binding Titrations 944.2.6. Protein crystallization, data collection, and structure determination 944.3. Results 974.3.1. Expression and purification of CYP105N1 974.3.2. Binding of ligands to CYP107G1 and CYP122A2 1004.3.3. Overall structure of CYP107G1 1034.4. Discussion 107Chapter 5. Conclusion 110References 113Appendix Human Cytochrome P450 1A2 Allelic Variants, P450 1A2*8, *15, and *16 (R456H, P42R, and R377Q) 1341. Introduction 1342. Materials and methods 1362.1. Chemicals and enzymes 1362.2. Construction of P450 1A2 mutants plasmids 1362.3. Expression of recombinant P450 1A2 mutants and membrane preparation 1372.4. Western blotting analysis 1372.5. Enzyme catalytic activity assays 1383. Results 1393.1. Expression of recombinant P450 1A2 variants 1393.2. Preparation of bicistronic membranes containing P450 1A2 wild type and P42R mutant 1423.3. Enzymatic activities of the P450 1A2 P42R variant 1443.4. Locations of the mutated residues in P450 1A2 variants 1484. Discussion 150Abstract (in Korean) 153