生产二硫键稳定的跨膜肽复合物的结构研究
Summary
膜嵌入蛋白结构域之间的相互作用的生物物理和生物化学的研究面临许多技术上的挑战，首先是获得适当的学习材料。本文描述了一种用于生产和纯化二硫键稳定的的跨膜肽复合物，是适合用于结构分析通过溶液的核磁共振（NMR）和其他的分析应用的协议。
Abstract
脂质嵌入的膜蛋白，α-螺旋结构域之间的物理相互作用起着至关重要的作用，在膜蛋白复合体的折叠和装配和跨膜（TM）信令和细胞表面蛋白水平的调节，例如动态过程。了解这些关联的特定序列的结构特点，需要复杂的生物物理和生物化学分析TM肽复合物。然而，TM域的极端疏水性使得它们非常难以操纵使用标准的肽化学技术，生产合适的学习材料常常被证明是令人望而却步具有挑战性的。确定的条件下，肽可以采用稳定的螺旋构象，并形成复合物， 自发地增加了更深一层的难度。在这里，我们提出了一种程序，均聚物或杂二聚体TM肽复合物，从材料的生产是在大肠杆菌中表达的关口，从而允许稳定同位素标签用于核磁共振（NMR）或其他应用程序相对廉价的非天然存在的氨基酸的掺入。在此方法中的关键的创新是作为共价结合 （二硫键交联的）组件改组为洗涤剂，脂质或其他膜-模拟物时，可以形成稳定的，化学计量的和均质的结构，TM配合物的生产和纯化。我们还提出了精心优化的程序也同样适用，无论是生产单TM域或交联复合物的表达和纯化，并提供这些方法来适应新的TM序列的意见。
Introduction
该协议的细节一个过程中，我们已开发生产出二硫键稳定的复合物的跨膜肽（TM）采用溶液NMR结构研究。这个过程需要利用所提供的强大的表达ΔtrpLE1413融合系统（见下文），并允许使用先进的稳定同位素标记技术，现代化的多维NMR实验TM肽复合物的定义组成。我们采用这些技术来确定的NMR结构淋巴细胞活化免疫受体如何从多个膜蛋白亚基组装TM域之间的相互作用（1）最近检讨发现重要的新信息。这些技术适用于许多其他的膜蛋白的系统，以及广泛的下游除了溶液的NMR分析方法。虽然这里给出的例子利用本地的半胱氨酸残基创建一个复杂的，模仿自然的二硫键键合的蛋白，设计是同样适合于创建工程二硫键稳定的复合物，通常是由较弱，均聚物和杂二聚体TM配合物的非共价相互作用，如保持在一起表皮生长因子受体（EGFR）家族蛋白2-4或异源二聚体αβ整合复合物5,6。
非常疏水的肽序列，如那些来自脂质双层跨越TM蛋白的部分是极为困难的课题，生物化学和生物物理研究。除了是非常具有挑战性的操作使用标准的蛋白质和多肽化学技术，他们往往对细胞的毒性，因此难以产生重组。我们7,8和9-11有显着的成功表达这样的困难在细菌的肽序列帧中的羧基端来自大肠杆菌的修改版本的ΔtrpLE1413序列融合到大肠杆菌色氨酸操纵12。 〜13 kDa的trpLE由该序列编码的多肽可以在T7启动子下的高的水平，并产生完全定位于包涵体的问题有关的毒性和/或不稳定的规避。该序列通过加入一种氨基末端9-组氨酸标记13和消除从trpLE序列内部蛋氨酸和半胱氨酸残基，14允许trpLE-肽融合到由金属离子亲和层析法进行纯化和消化使用溴化氰（CNBr改性），以释放所需的肽序列。我们已经成功地使用这个系统来表达更多的十几家不同序列的trpLE融合膜蛋白片段包含多达四个TM域名（7,8和未公布结果;也见讨论部分）。
“在本协议中的关键创新是确定的条件下，其中的的非结构化和难溶trpLE-TM融合可以有效地二硫键交联的背景下，一个精简的工作流程。高收益的表达，处理和纯化的多肽产品的几个方面也得到了彻底的优化，这里提出的建议同样适用于非二硫键交联（单体）TM肽产品的生产。
Protocol
Representative Results
Discussion
根据我们的经验， 表达的融合trpLE-TM。trpLE-TM融合低表达丰富的培养基中在37℃下，和这里所描述的培养条件为许多不同的序列，含有一至四个TM域，产率范围已证明是成功的为50〜150 mg / L的纯的，完整的融合。融合编码三-或四-TM G蛋白偶联受体片段（人CCR5 TM1-TM3和TM4-TM7分别）或人类信号肽肽酶（4 TM域;见文献15）的芯催化片段代表在此范围内的最低的表达的水平，而这里所使用的序…
Divulgazioni
The authors have nothing to disclose.
Acknowledgements
这项工作的经费是由国家健康与医学研究委员会，澳大利亚（NHMRC项目赠款1011352 MEC和澳门赛马会，独立研究机构基础设施支援计划IRIISS拨款，以WEHI）和维多利亚州政府（VESKI创新奖学金MEC;维多利亚州政府运营基础设施的支持WEHI）。 MEC是一个英国女王伊丽莎白二世的澳大利亚研究委员会研究员。 EFXB承认，从诺玛·希尔达·舒斯特在墨尔本大学的奖学金的支持。
Materials
| Name of Reagent/Material | Company | Catalogue Number | Comments |
| Cyanogen bromide | ALDRICH | P.No- C91492,CAS-506-68-3 | HAZARDOUS SUBSTANCE. DANGEROUS GOODS. Very toxic by inhalation, in contact with skin and if swallowed. Contact with acids liberates very toxic gas. Very toxic to aquatic organisms, may cause long-term adverse effects in the aquatic environment. |
| Trifluoroacetic acid | SIGMA-ALDRICH | P.CODE-1000984387, CAS Number 76-05-1 | HAZARDOUS SUBSTANCE. DANGEROUS GOODS., Causes severe burns. Harmful by inhalation. Harmful to aquatic organisms, may cause long-term adverse effects in the aquatic environment. |
| 2-Mercaptoethanol | SIGMA-ALDRICH | P.No M7154, CAS Number 60-24-2 | HAZARDOUS SUBSTANCE. DANGEROUS GOODS. Toxic by inhalation, in contact with skin and if swallowed. Irritating to skin. Risk of serious damage to eyes. May cause sensitization by skin contact. Very toxic to aquatic organisms, may cause long-term adverse effects in the aquatic environment. |
| 1,1,1,3,3,3-Hexafluoro-2-propanol | SIGMA-ALDRICH | Product Number 52512, CAS-No. 920-66-1 | HAZARDOUS SUBSTANCE. DANGEROUS GOODS. Harmful by inhalation and if swallowed. Causes burns. |
| Formic acid | Merck KGaA | K41186564 | Flammable liquid and vapour. Causes severe skin burns and eye damage. |
| Urea | UNIVAR, AJAX FINECHEM | Product Number, 817, CAS-No 57-13-6 | When heated, decomposes to carbon dioxide and ammonia; if burned, emits small amounts of nitrogen oxides. Can cause redness and irritation of skin and eyes. |
| GUANIDINE HYDROCHLORIDE | Amresco | P.No-M110, CAS Number: 50-01-1 | Harmful if swallowed, Causes serious eye irritation,Causes skin irritation, Acute Toxicity Oral, Skin Irritant, Eye Irritant. |
| TRITON X-100 | SIGMA | Product Number- T8532 CAS No: 9002-93-1 | Triton X-100 is a nonionic detergent, 100% active ingredient, which is often used in biochemical applications to solubilize proteins. Triton X-100 has no antimicrobial properties and considered a comparatively mild non-denaturing detergent |
| His-Select Nickel-Affinity gel | SIGMA-ALDRICH | Catalog Num- P6611 | IS-Select Nickel Affinity Gel is an immobilized metal- ion affinity chromatography (IMAC) product. The HIS-Select Nickel Affinity gel is a proprietary quadridentate chelate on beaded agarose charged with nickel that is designed to specifically bind histidine containing proteins. |
| (-)-Glutathione, oxidized | SIGMA-ALDRICH | Catalog num 150568 | |
| Misonix S-3000 sonicator | QSONICA | S-3000 (discontinued) | Max power output 600 watts. 1/2-inch replaceable-tip probe takes 1/2-inch high-intensity, high-volume tips and a range of high-intensity, low-volume tips. Closest models currently available from this company are Q500 and Q700. |
| RP-HPLC: BioLogic DuoFlow chromatography system, Software Version 5.3 | Bio-Rad Laboratories | Catalog Num 760-0047, Config No: AU500571, Serial No: 484BR3705 | Peptides binds to reverse phase HPLC columns in high aqueous mobile phase and are eluted from RP HPLC columns with high organic mobile phase. In RP HPLC peptides are separated based on their hydrophobic character. Peptides can be separated by running a linear gradient of the organic solvent. |
| Prep HT C3 ZORBAX 300SB-Analytical HPLC Column, 21.2 x 150 mm, 5 μm particle size | Agilent | Product No: 895150-909 | Reversed-phase HPLC colum |
| NuPAGE 12% Bis-Tris Gels | Life Technologies | NP0341BOX | Pre cast gels for protein electrophoresis |
| Slide-A-Lyzer G2 Dialysis Cassettes, 3.5K MWCO | Thermo Scientific | Product No: 87724 | Sample dialysis |
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