BioVector® pTip-QC2 Inducible Rhodococcus-E. coli Shuttle Expression Vector / pTip-QC2 硫丝链霉素诱导型红球菌-大肠杆菌穿梭表达质粒

一 产品基本信息与分子生物学背景

• 质粒名称：pTip-QC2。

• 载体类型与宿主系统：广谱放线菌/红球菌表达穿梭质粒（Rhodococcus-E. coli Shuttle Vector）。pTip-QC2 是工业微生物学和合成生物学中专用于放线菌门（Actinobacteria），特别是红球菌属（Rhodococcus spp.，如 R. erythropolis, R. jostii RHA1, R. opacus）以及部分分枝杆菌属（Mycobacterium spp.，如 M. smegmatis mc²-155）的高效异源表达核心质粒。在工业生物催化中，红球菌和分枝杆菌因其具有极强的复杂有机物、甾体（Steroids）降解能力和独特的代谢广谱性，被视为优秀的细胞工厂底盘。然而，许多复杂的放线菌源单加氧酶、多亚基复合酶在大肠杆菌（E. coli）系统中表达常出现包涵体、无活性或表达量极低的问题。由 Nakashima 与 Tamura 团队开发的 pTip 系列穿梭载体，正是为了攻克这一瓶颈而设计的严紧型、可调控的放线菌专用表达系统。

• 核心元件图谱（插入片段与调控构型）：

  • 诱导型启动子（Promoter）：核心采用源自发利斯链霉素的 $P_{tipA}$ 启动子（Thiostrepton-inducible promoter）。该启动子具有极高的严紧性（漏表达极低）和超强的诱导转录放大效应。

  • 化学诱导剂（Inducer）：硫丝链霉素（Thiostrepton）。在培养物中只需加入极微量（通常工作浓度为 $1\ \mu\text{g/mL}$ 左右）的硫丝链霉素，即可通过激活宿主体内的 TipA 调节蛋白，诱导 $P_{tipA}$ 下游目的基因发生爆发式高效转录。

  • 多克隆位点（MCS）分类：命名中的 "QC2" 带有精确的元件编码：

    • "Q"：代表该质粒的放线菌复制子来源于红球菌隐蔽质粒 pRE2895 的 repAB 操纵子（repAB replicon）。

    • "C"：代表其真核/放线菌筛选压力为氯霉素抗性基因（Chloramphenicol resistance, $Chl^R$）。

    • "2"：代表其多克隆位点采用 Type 2 型构型（配有特异性的限制性内切酶切位点组合，如 $Nco\text{I}, ~Bsp\text{HI}, ~Bam\text{HI}, ~Hind\text{III}$ 等，通常带有一个嵌入式 $6\times\text{His}$ 纯化标签）。

• 穿梭克隆与筛选构型（双系统骨架特征）：

  • 大肠杆菌复制子：携带高拷贝的大肠杆菌 ColE1/pUC ori 复制起始位点，方便在常规大肠杆菌宿主中进行大规模高丰度克隆、测序与质粒提取。

  • 放线菌复制子：携带 pRE2895 源的 repAB 操纵子，可在红球菌属和分枝杆菌属细胞内实现自主稳定性复制。

  • 原核/宿主抗性组合：在大肠杆菌阶段通常利用骨架自带的氨苄青霉素抗性（Ampicillin, $Amp^R$）或大肠杆菌兼容的氯霉素抗性进行筛选；而在转入红球菌/分枝杆菌后，必须使用氯霉素（Chloramphenicol,$Chl^R$）实施放线菌层面的正向选择压力。

二 核心科研价值与复杂放线菌酶学/环境生物学应用

pTip-QC2 作为突破大肠杆菌局限性的放线菌标志性高产质粒，广泛应用于以下前沿领域：

1. 复杂环境降解酶（如气态烃单加氧酶）的体内重建与表型互补：许多环境微生物中的关键降解酶（如用于降解 1,4-二氧六环、四氢呋喃、丙烷的双核铁单加氧酶 mimABCD 或 prmABCD 基因簇）具有极其复杂的全酶结构。将这些 4-5 基因组成的庞大操纵子直接克隆至 pTip-QC2，转入红球菌或耻垢分枝杆菌中，可在硫丝链霉素诱导下实现正确折叠、辅因子高效组装且具备完整催化活性的异源全酶表达。

2. 甾体/胆固醇代谢通路（Steroid Uptake & Metabolism）的功能研究：在研究诸如结核分枝杆菌（M. tuberculosis）或红球菌中控制甾体和胆固醇转运的 mce4 操纵子（含 11 个基因）时，pTip-QC2 常作为基因缺失突变株的功能回复与互补表达载体（Complementation vector），用以确证靶向基因在病原体感染和代谢中的核心功能。

3. 多质粒兼容性共表达系统的构建（Multiple Protein Co-expression）：由于 pTip-QC2 采用的是 pRE2895（repAB）复制起始位点，它与采用 pRE8424（rep）滚动循环复制子的 pTip-RC 系列质粒，或者带有四环素抗性的 pTip-QT 系列质粒具有完美的质粒相容性（Compatibility）。科研人员可以同时将 pTip-QC2 和另一株兼容质粒协同电转入同一个红球菌细胞内，实现多种重组蛋白或复杂多组分代谢通路的体外完美共表达。

三 实验室大肠杆菌克隆、红球菌电转化与硫丝链霉素诱导标准步骤

1. 大肠杆菌中的质粒扩增与高纯度提取

• 推荐宿主感受态：大肠杆菌 DH5$\alpha$、Top10 或大肠杆菌 JM109。

• 原核抗生素选择压力：LB 培养基中添加 $100\ \mu\text{g/mL}$ 氨苄青霉素（Ampicillin） 或 $25\ \mu\text{g/mL}$ 氯霉素（Chloramphenicol）（依据质粒批次，双抗性标记均支持大肠杆菌阶段克隆选择）。

• 操作流线：

  1. 取 1 $\mu$L 纯化 pTip-QC2 空载或重组质粒，投入 50 $\mu$L 的大肠杆菌感受态细胞中。

  2. 冰置 30 分钟，42 ℃ 热激 45 秒，迅速放回冰上 2 分钟。

  3. 加入 250 $\mu$L 液体 LB 培养基，37 ℃ 振荡复苏 60 分钟。

  4. 涂布于含药 LB 平板上，37 ℃ 倒置培养过夜。

  5. 挑取单菌落接入 5 - 10 mL 含药液体 LB 中，37 ℃、250 rpm 培养 12 - 14 小时，使用标准质粒小提试剂盒（Miniprep Kit）获取高浓度质粒。

2. 红球菌/分枝杆菌的高效电转化步骤（Electroporation Protocol）

放线菌的细胞壁含有极厚的霉菌酸（Mycolic acid）和脂质，常规化学转化法（如 $CaCl_2$）彻底无效，必须通过高压电击转化法将 pTip-QC2 导入宿主中：

1. 制备电转感受态（以红球菌为例）：

   • 将红球菌（如 R. erythropolis）接入含优质营养的 LB 或 LB-sucrose（含 0.5% 蔗糖）液体培养基中，30 ℃ 培养至对数生长中期（$OD_{600} = 0.6 - 0.8$）。

   • 离心收集菌体，用冰预冷的无菌 10% 灭菌甘油溶液（或 10% 甘油 + 0.5 M 蔗糖洗涤液）连续反复洗涤沉淀 3 - 4 次，以彻底去除介质中的离子。

   • 最后的菌泥用少量 10% 甘油重悬，分装为 50 - 100 $\mu$L 铝箔管，置于 -80 ℃ 冰箱冻存。

2. 高压电击转化：

   • 取 1 管放线菌电转感受态细胞于冰上融化，加入 200 - 500 ng 的 pTip-QC2 质粒 DNA（体积勿超过感受态体积的 10%），轻柔混匀，全量转移至冰预冷的 0.1 cm 或者是 0.2 cm 间距的电转杯（Electroporation Cuveette）中。

   • 设定电转仪参数：电压：$1.8 - 2.5\ \text{kV}$（0.1 cm 杯推荐 1.8 kV，0.2 cm 杯推荐 2.5 kV），电容 $25\ \mu\text{F}$，电阻 $200 - 400\ \Omega$。

   • 实施电击。击发后迅速向电转杯中注入 1 mL 预热的 SOC 或者是 LB 液体培养基，用移液枪吸出转移至 1.5 mL 离心管中。

3. 复苏与红球菌氯霉素压选（放线菌核心质控）：

   • 将电击后的红球菌悬液置于 30 ℃ 摇床中，150 rpm 温和振荡复苏培养 3 - 4 小时。注：放线菌生长和抗性蛋白合成极慢，复苏时间必须拉长至 3 小时以上，否则氯霉素压选时会导致细胞成片死亡，转化率归零。

   • 复苏结束后，离心富集菌体，涂布于含有 $25 - 34\ \mu\text{g/mL}$ 氯霉素（Chloramphenicol）的 LB 固体选择性琼脂平板上。

   • 置于 30 ℃ 恒温孵箱中培养 48 - 72 小时（分枝杆菌可能需要 3 - 5 天），直至表面长出饱满的放线菌转化子阳性单菌落。

3. 硫丝链霉素诱导蛋白表达与功能质检流线

1. 挑取验证正确的 pTip-QC2 重组红球菌单菌落，接入含有 25 $\mu$g/mL 氯霉素的 LB 液体培养基中，30 ℃、200 rpm 摇菌培养过夜，作为种子液。

2. 按 1:50 或者是 1:100 的比例将种子液转接至新鲜的含氯霉素的表达培养基中。

3. 动态监测生长。当细胞培养物的 $OD_{600}$ 达到 0.4 - 0.6 之间（处于对数生长初期向中期过渡阶段）时，开启化学诱导。

4. 精确投放化学诱导剂：向培养体系中注入适量硫丝链霉素（Thiostrepton）储备液，使其终浓度精确维持在 $1\ \mu\text{g/mL}$（可根据具体重组蛋白的溶解度，在 $0.5 - 5\ \mu\text{g/mL}$ 范围内实施浓度梯度优化）。

5. 控温孵育：根据目的蛋白的性质调控培养瓶温度：

   • 常规可溶性蛋白：维持在 30 ℃ 连续诱导培养 12 - 16 小时。

   • 极易形成包涵体的敏感放线菌酶（核心优势）：可将摇床温度直接下调至 15 ℃ - 20 ℃ 实施超低温缓慢诱导 24 - 36 小时。红球菌系统在 4 ℃ - 15 ℃ 仍具备优异的合成与翻译活性，能让极其复杂的单加氧酶最大限度保持完全可溶状态。

6. 细胞收获与表达分析：离心收集细胞泥，通过超声波破碎（Sonicator）或放线菌专用溶菌酶裂解细胞，分级提取全细胞裂解液、上清液和沉淀段。通过 SDS-PAGE 电泳或 Western Blot（抗 His-tag 标签抗体抗性），在目标分子量处确证靶向重组放线菌全酶的成功过表达。

Part 2 English Section

I Product General Information and Molecular Background

• Plasmid Nomenclature: pTip-QC2.

• Vector Class and Target Expression Framework:Actinobacteria-specific Inducible Shuttle Vector (Rhodococcus-E. coli Shuttle System).The pTip-QC2 platform represents a specialized, high-efficiency molecular tool designed for engineering heterologous gene expression within the phylum Actinobacteria, focusing tightly on the genera Rhodococcus spp. (e.g.,R. erythropolis,R. jostii RHA1,R. opacus) and specific Mycobacterium spp. strains (such as M. smegmatis mc²-155).In industrial biocatalysis, Rhodococci are recognized as elite host factories owing to their exceptional metabolic capability to degrade complex environmental pollutants and process sterols. However, many actinobacterial-derived multi-subunit monooxygenases form insoluble inclusion bodies or lose catalytic activity when expressed in traditional E. coli systems. To resolve this functional bottleneck, Nakashima and Tamura developed the pTip vector family, yielding a tightly regulated, highly responsive expression system tuned specifically for actinomycetals.

• Core Expression Elements and Architecture:

  • Inducible Promoter: Driven by the highly stringent and responsive $P_{tipA}$ promoter derived from Streptomyces lividans. This sequence exhibits negligible basal leakage in the uninduced state but delivers immense transcriptional amplification upon activation.

  • Chemical Inducing Reagent:Thiostrepton. Administered at minuscule working concentrations (typically around $1\ \mu\text{g/mL}$), thiostrepton complexes with the host's endogenous TipA regulatory protein to initiate a massive transcriptional burst from the downstream $P_{tipA}$ locus.

  • Nomenclature and Cloning Coordinate Coding ("QC2"):

    • "Q": Specifies that the vector utilizes an actinobacterial replication origin derived from the Rhodococcus cryptic plasmid pRE2895, operating via the repAB operon (repAB replicon).

    • "C": Denotes that the target selection pressure marker for host maintenance is the Chloramphenicol resistance gene ($Chl^R$).

    • "2": Designates the integration of a Type 2 Multiple Cloning Site (MCS) configuration, outlining distinct restriction recognition sites ($Nco\text{I}, ~Bsp\text{HI}, ~Bam\text{HI}, ~Hind\text{III}$, etc.) paired with an integrated $6\times\text{His}$ fusion purification tag.

• Shuttle Maintenance and Dual Selection Parameters:

  • E. coli Origin: Outfitted with a high-copy ColE1/pUC ori replication origin to facilitate high-yield plasmid propagation, sequence validation, and miniprep isolation inside standard E. coli cloning strains.

  • Actinobacterial Origin: Outfitted with the pRE2895 repAB operon to ensure stable autonomous plasmid maintenance inside Rhodococcus and Mycobacterium lineages without chromosomal integration.

  • Antibiotic Resistance Selection: Propagated inside competent E. coli using either Ampicillin resistance ($Amp^R, 100\ \mu\text{g/mL}$) or chloramphenicol selection. Once electroporated into downstream actinobacterial hosts, target selection relies strictly on Chloramphenicol ($Chl^R$) supplementation.

II Strategic Research Value and Complex Biocatalytic Applications

The pTip-QC2 vector bypasses the expression limits of traditional proteobacterial hosts, making it a powerful tool for environmental and metabolic engineering:

1. Reconstruction of Complex Multi-Subunit Environmental Monooxygenases:Many environmental degradation pathways depend on multicomponent enzymes, such as gaseous alkane/propane monooxygenases (mimABCD or prmABCD gene clusters) responsible for clearing 1,4-dioxane and tetrahydrofuran. Cloning these large, multi-gene operons into pTip-QC2 and transforming them into Rhodococcus or M. smegmatis yields correctly folded, cofactor-assembled, and catalytically active heterologous holoenzymes upon thiostrepton induction.

2. Deciphering Steroid and Cholesterol Metabolism Pathways:When dissecting massive operons like the 11-gene mce4 locus—which governs steroid and cholesterol transport in R. jostii RHA1 and M. tuberculosis—pTip-QC2 serves as an excellent complementation vector. It allows researchers to reintroduce wild-type genes into knockout strains to definitively validate gene functions during pathogenicity or metabolic profiling.

3. Engineering Multi-Plasmid Co-Expression Networks:Because pTip-QC2 is driven by the pRE2895 (repAB) replicon, it is fully compatible with pTip-RC vectors, which use a rolling-circle pRE8424 (rep) origin, as well as tetramine-resistant pTip-QT variants. This structural compatibility allows investigators to co-transform pTip-QC2 alongside complementary plasmids into a single Rhodococcus cell, enabling the synchronized expression of multi-protein complexes or extended metabolic pathways.

III Laboratory Bacterial Cloning, Actinobacterial Electroporation, and Protein Induction Protocols

1. Plasmid Propagation and Isolation in Escherichia coli

• Recommended Competent Host Strain:Escherichia coli DH5$\alpha$, Top10, or JM109.

• Bacterial Antibiotic Selection Matrix: Supplement standard LB broth/agar with $100\ \mu\text{g/mL}$ Ampicillin or $25\ \mu\text{g/mL}$ Chloramphenicol.

• Execution Workflow:

  1. Introduce 1 $\mu$L of purified pTip-QC2 plasmid DNA (empty vector or recombinant construct) into a 50 $\mu$L aliquot of competent DH5$\alpha$ cells.

  2. Incubate on ice for 30 minutes, heat-shock at 42 °C for 45 seconds, and transfer back to ice for 2 minutes.

  3. Add 250 $\mu$L of standard SOC or LB broth and recover at 37 °C with shaking at 220 rpm for 60 minutes.

  4. Plate the culture onto selective LB agar plates and incubate inverted at 37 °C overnight.

  5. Inoculate an isolated colony into 5 – 10 mL of selective LB broth. Incubate at 37 °C with shaking at 250 rpm for 12 – 14 hours, then extract high-purity plasmid using a standard commercial miniprep kit.

2. High-Voltage Electroporation Matrix for Rhodococcus Strains

Because the cell walls of Actinobacteria are packed with dense mycolic acids and complex lipids, standard chemical transformation methods are ineffective.pTip-QC2 must be introduced via high-voltage electroporation:

1. Preparation of Electrocompetent Cells:

   • Cultivate the target Rhodococcus strain in rich LB broth or LB supplemented with 0.5% w/v sucrose at 30 °C until it hits mid-log phase ($OD_{600} = 0.6 - 0.8$).

   • Pellet the biomass via centrifugation and wash the cells 3 to 4 times with ice-cold, sterile 10% v/v glycerol solution (or a 10% glycerol + 0.5 M sucrose wash matrix) to completely eliminate residual ions and prevent electrical arcing.

   • Resuspend the final concentrated pellet in a minimal volume of 10% glycerol, aliquot into 50 – 100 $\mu$L volumes, flash-freeze, and store at -80 °C.

2. Electroporation Pulsing:

   • Thaw one aliquot of electrocompetent cells on ice. Add 200 – 500 ng of pure pTip-QC2 plasmid DNA, ensuring the DNA volume does not exceed 10% of the cell volume, and mix gently. Transfer the mixture into an ice-chilled 0.1 cm or 0.2 cm electroporation cuvette.

   • Calibrate the electroporator to the following parameters:Voltage: $1.8 - 2.5\ \text{kV}$ (1.8 kV for 0.1 cm cuvettes; 2.5 kV for 0.2 cm cuvettes), capacitance at $25\ \mu\text{F}$, and resistance at $200 - 400\ \Omega$.

   • Pulse the sample. Immediately add 1 mL of pre-warmed SOC or LB recovery broth directly into the cuvette, pipette gently to mix, and transfer the mixture to a sterile 1.5 mL tube.

3. Outgrowth and Chloramphenicol Selection (Critical Step):

   • Incubate the pulsed cells at 30 °C with gentle shaking at 150 rpm for 3 to 4 hours.CRITICAL CONTROL VALUE: Because Actinobacteria exhibit slow growth and delayed antibiotic marker synthesis, an extended outgrowth phase of at least 3 hours is mandatory. Skipping or shortening this step will cause total cell death upon chloramphenicol exposure, reducing transformation efficiency to zero.

   • Following outgrowth, pellet the cells gently, resuspend in 100 $\mu$L of residual medium, and spread onto selective LB agar plates containing $25 - 34\ \mu\text{g/mL}$ Chloramphenicol.

   • Incubate at 30 °C for 48 – 72 hours (up to 5 days for slower-growing Mycobacteria) until robust, isolated colonies appear.

3. Thiostrepton-Mediated Protein Expression and Harvesting Workflow

1. Inoculate a sequence-verified pTip-QC2 recombinant Rhodococcus colony into 5 mL of selective LB broth containing 25 $\mu$g/mL chloramphenicol. Cultivate at 30 °C with shaking at 200 rpm overnight to establish a starter culture.

2. Back-dilute the starter culture 1:50 or 1:100 into fresh production medium supplemented with chloramphenicol.

3. Monitor cell growth under standard conditions. Initiate chemical induction when the culture $OD_{600}$ reaches 0.4 – 0.6 (the ideal transition window from early to mid-log phase).

4. Targeted Inducer Delivery: Supplement the culture with a sterile stock solution of thiostrepton to achieve a final working concentration of $1\ \mu\text{g/mL}$. (This parameter can be optimized between $0.5$ and $5\ \mu\text{g/mL}$ depending on target protein solubility profiles).

5. Thermal Management and Incubation: Adjust the shaker temperature based on the architectural complexity of the target enzyme:

   • Standard Soluble Proteins: Maintain incubation at 30 °C with shaking for 12 – 16 hours.

   • Insoluble-Prone Enzymes (Core System Advantage): Lower the incubator temperature to 15 °C – 20 °C and induce slowly for 24 – 36 hours. The Rhodococcus host system maintains robust translation pathways at these lower temperatures, maximizing the yield of correctly folded, soluble multi-subunit monooxygenases.

6. Harvest and Expression Assessment: Spin down the biomass, and disrupt the cells using probe sonication or actinobacteria-optimized lysozyme lysis buffers. Clarify the lysate via high-speed centrifugation into soluble supernatant and insoluble pellet fractions. Analyze the samples via SDS-PAGE or Western Blotting (using anti-His-tag antibodies) to confirm high-level, soluble expression of the target protein at its expected molecular weight.

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