BioVector? KM13 輔助噬菌體

BioVector? KM13 Helper Phage

第一部分 中文說明

一 產(chǎn)品基本信息與科研用途

• 產(chǎn)品名稱：BioVector? KM13 輔助噬菌體

• 基因組分類：單鏈 DNA（ssDNA）絲狀噬菌體（基于 M13 噬菌體改構）。

• 核心用途：專門用于噬菌體展示技術（Phage Display）中的高通量抗體/多肽文庫篩選（Biopanning）。KM13 是一種典型的含有“蛋白酶切位點”的特殊輔助噬菌體，旨在通過化學促選手段，極其劇烈地提高針對高親和力靶標的淘選效率和克隆回收率。

• 抗性選擇標記：帶有 卡那霉素抗性基因（Kanamycin，$Km^R$）。這一設計便于在共感染大腸桿菌宿主時，通過抗生素加壓篩選出成功裝配的輔助噬菌體。

• 常用宿主菌：大腸桿菌抗性/缺陷型菌株（如 TG1、XL1-Blue、ER2738、SS320 等帶有 $F'$ 因子纖毛的菌株）。

二 關鍵結構域與酶切促選（Trypsin-cleavable）機制

• 傳統(tǒng) M13 輔助噬菌體（如 M13KO7、VCSM13）的瓶頸：在利用常規(guī)噬菌體表達載體（Phagemid）進行抗體文庫包裝時，由于 phagemid 只編碼外源抗體-pIII 融合蛋白而缺乏其他結構基因，必須依靠野生型結構的輔助噬菌體來提供完整的衣殼蛋白和復制酶。然而，輔助噬菌體自身帶有完整的、未融合的野生型 pIII 基因（負責結合大腸桿菌纖毛進而完成侵染）。

  • 這會導致最終包裝排出的噬菌體顆粒中，絕大多數(shù)都裝配了野生型的 pIII 蛋白（稱為“空載顆粒”），而非展現(xiàn)外源抗體的融合蛋白。在淘選（Biopanning）過程中，這些不表達抗體但具備超級侵染力的空載噬菌體會造成極高的物理背景殘留。

• KM13 的分子改構與胰蛋白酶切選機制（$\Delta pIII$ 蛋白酶原敏感性突變）：

  • 改構核心：BioVector? KM13 對其自身的 pIII 外膜衣殼蛋白編碼區(qū)進行了精準工程化改造，在 pIII 蛋白的突觸結構域（N1 與 N2 結構域之間）引入了一個高度特異性的胰蛋白酶（Trypsin）剪切位點。

  • 促選原理：

    1. 在包裝出的混合噬菌體文庫中，由 KM13 貢獻的衣殼蛋白帶有胰蛋白酶敏感位點；而由 Phagemid 載體（如 pCANTAB 5E、pHEN2）驅動表達的外源抗體-pIII 融合蛋白由于去除了該敏感位點，對胰蛋白酶表現(xiàn)為天然耐受。

    2. 在噬菌體與靶抗原結合、洗滌去除未結合的顆粒后，直接向孔內加入適量的 胰蛋白酶（Trypsin） 進行短時間溫育。

    3. 此時，所有未展示異源抗體、純粹由輔助噬菌體衣殼組裝的“空載”顆粒其 pIII 蛋白會發(fā)生全面斷裂，徹底喪失侵染大腸桿菌的能力。

    4. 相比之下，那些真正展示了高親和力抗體的重組噬菌體顆粒，由于抗體-pIII 融合鏈不被剪切，依然能夠完整無損地高效侵染宿主菌 TG1 進行擴增。該技術通過化學“淘汰法”，將文庫淘選的背景假陽性率降低了數(shù)個數(shù)量級。

三 標準噬菌體文庫包裝與淘選步驟

1. 噬菌體超感染包裝（Helper Phage Superinfection）：

   • 將含有重組抗體 Phagemid 文庫的大腸桿菌 TG1 接種于 2x YT（含 2% 葡萄糖和氨芐青霉素）液體中，37 攝氏度振蕩培養(yǎng)至對數(shù)生長中期（$OD_{600} = 0.4 \sim 0.5$）。

   • 按感染復數(shù) MOI = 10 到 20 的比例加入定量的 BioVector? KM13 輔助噬菌體液，37 攝氏度靜置保溫 30 分鐘以令其吸附。

   • 離心去除富含葡萄糖的舊培養(yǎng)基（葡萄糖會阻遏 lac 啟動子），用不含葡萄糖、但含有氨芐青霉素和卡那霉素（$50 \ \mu\text{g/mL}$）的 2x YT 新鮮培養(yǎng)基重懸，30 攝氏度（或 25 攝氏度低速）過夜振蕩培養(yǎng)包裝。

2. 噬菌體沉淀與分級回收：

   • 次日離心收獲過夜培養(yǎng)基上清，加入 1/5 體積的 PEG/NaCl 沉淀液（20% PEG 8000, 2.5 M NaCl），冰浴放置 1 小時。

   • 超速或常規(guī)高轉速離心沉淀，用無菌 PBS 緩沖液重懸沉淀顆粒，獲得滴度在 $10^{12} \sim 10^{13} \ \text{pfu/mL}$ 的 KM13 包裝文庫。

3. 胰蛋白酶促選洗脫法（Trypsin Elution / Selection）：

   • 依照標準固相包被法將靶抗原固定于 Immunotube 或 96 孔板中，加入重懸的噬菌體文庫孵育 2 小時。

   • 使用 PBST 緩沖液進行常規(guī) 10 到 20 次的強力洗滌，以完全去除物理粘附的未結合病毒。

   • 洗滌結束后，向孔內加入最終濃度為 $1 \ \text{mg/mL}$ 的精制胰蛋白酶（Trypsin） 溶液，室溫溫育 10 到 15 分鐘。胰蛋白酶不僅能通過降解 KM13 pIII 蛋白來癱瘓空載噬菌體，還能高效洗脫已經(jīng)結合的高親和力特異性克隆。

   • 迅速收集洗脫液，直接中和并投入新制備的對數(shù)期大腸桿菌 TG1 液體中，37 攝氏度侵染擴增，進入下一輪淘選循環(huán)。

四 核心科研應用方向

1. 超大規(guī)模全人源單克隆抗體文庫（ScFv / Fab Library）的特異性淘選：BioVector? KM13 是全球抗體工程與高通量藥物篩選核心實驗室、研究機構首選的高效輔助噬菌體系統(tǒng)。它尤其適用于從 $10^{10}$ 以上庫容的天然全人源單鏈抗體文庫中，富集和篩選針對微量高毒性抗原、腫瘤特異性膜受體的高親和力中和抗體克隆。

2. 靶向高難度膜蛋白（GPCRs）與微量復雜糖蛋白的噬菌體展示文庫篩選：由于 7 次跨膜蛋白（GPCR）等靶點在體外極難維持天然構象且背景結合率極高，使用 KM13 進行文庫包裝可在淘選洗脫階段運用“胰蛋白酶滅活法”，最大程度上消除因物理非特異性吸附導致的假陽性克隆膨脹。

3. 基于噬菌體表面展示的腫瘤靶向歸巢肽（Homing Peptides）體內篩選（In vivo Panning）：在活體動物內注射多肽文庫進行器官特異性歸巢肽篩選時，回收的組織樣本常含有大量非特異性殘留顆粒。利用 KM13 的胰蛋白酶敏感特性，可在回收后進行體外酶解，從而精準捕獲真正靶向內皮細胞的高效肽段載體。

PART 2 ENGLISH SECTION

I General Information and Applications

• Product Name: BioVector? KM13 Helper Phage

• Genomic Classification: Single-Stranded DNA (ssDNA) Filamentous Phage (engineered M13 phage derivative).

• Primary Application: Specialized for high-throughput biopanning and antibody/peptide selection within Phage Display technology platforms. KM13 represents a premier textbook "trypsin-cleavable" helper phage designed to drastically enhance selection stringency against low-abundance or high-affinity targets via strategic chemical inactivation.

• Selection Flags: Houses a functional Kanamycin resistance gene ($Knamycin, Km^R$) configured into its genome, allowing for streamlined selective pressure application when coordinating multi-plasmid replication workflows inside E. coli.

• Common Host Systems: E. coli strains carrying the $F'$ episome pili architecture (e.g., TG1, XL1-Blue, ER2738, SS320).

II Architecture and Trypsin-Cleavable Selection Mechanics

• Limitations of Legacy Systems (e.g., M13KO7, VCSM13): When utilizing phagemid vectors to express an antibody library, the phagemid itself provides only the heterologous antibody-pIII fusion block but lacks all other structural and replicative codes. It relies on a helper phage to complement the missing machinery. However, classic helper phages introduce their own fully un-fused, highly infectious wild-type pIII capsids into the packaging pool.

  • This creates a scenario where the overwhelming majority of egressed viral progeny carry wild-type pIII arrays (termed "empty or passenger particles") instead of the target antibody fusion. During biopanning cycles, these non-displaying but highly infectious contaminants generate major non-specific binding and physical background noise.

• KM13 Design and Trypsin-Cleavable Differentiation Core ($\Delta pIII$ Protease-Sensitive Engineering):

  • Molecular Modification: BioVector? KM13 features a highly specific, genetically engineered trypsin cleavage site integrated into its own pIII minor coat protein matrix, positioned precisely between the N1 and N2 structural domains.

  • Selection Workflow:

    1. In an amplified hybrid phage library pool, the coat proteins contributed by KM13 maintain high susceptibility to trypsin degradation; conversely, the heterologous antibody-pIII fusions driven by the phagemid vectors (e.g., pCANTAB 5E, pHEN2) lack this protease-sensitive target and are naturally resistant.

    2. Following library engagement against immobilized target antigens and consecutive vigorous washing routines, the assay matrix is briefly treated with a calibrated dose of Trypsin.

    3. This enzymatic step cleaves the pIII structures of empty, non-displaying phages, leaving them unable to infect E. coli.

    4. Meanwhile, the true antibody-displaying clones remain structurally sound, retaining full infectivity to transform log-phase TG1 hosts for downstream amplification. This biochemical elimination method dramatically drives down false-positive rates by multiple orders of magnitude.

III Library Packaging and Trypsin-Driven Biopanning Protocols

1. Helper Phage Superinfection Execution:

   • Cultivate an E. coli TG1 library carrying the recombinant phagemid constructs in 2x YT media (supplemented with 2% glucose and ampicillin) at 37 degrees Celsius with vigorous shaking until reaching mid-log phase ($OD_{600} = 0.4 \sim 0.5$).

   • Inoculate the cell suspension with BioVector? KM13 helper phage liquid at a standard Multiplicity of Infection of MOI = 10 to 20. Incubate undisturbed at 37 degrees Celsius for 30 minutes to facilitate pilus attachment and genome injection.

   • Pellet the biomass to fully eliminate residual glucose (purging catabolite repression blocks off the lac promoter). Resuspend the cell mass in fresh glucose-free 2x YT broth enriched with both Ampicillin and Kanamycin ($50 \ \mu\text{g/mL}$), and run an overnight expression layout at 30 degrees Celsius (or 25 degrees Celsius for optimized folding configurations).

2. Phage Isolation and Concentration via PEG Precipitation:

   • Clarify the overnight culture matrix via high-speed centrifugation, harvest the virus-rich supernatant, and mix with a 1/5 volume of standard PEG/NaCl solution (20% PEG 8000, 2.5 M NaCl). Chill on ice for 1 hour to precipitate the viral structures.

   • Centrifuge to collect the phage pellet, and resuspend thoroughly in sterile PBS buffer, adjusting baseline functional titers to approximately $10^{12} \sim 10^{13} \ \text{pfu/mL}$.

3. Trypsin Selection & Elution Routine:

   • Apply the concentrated KM13-packaged library to immunotubes or ELISA wells pre-coated with the specific target antigen, allowing binding for 2 hours.

   • Wash the matrices rigorously 10 to 20 times with PBST buffer to thoroughly clear non-specific, physically trapped background viral units.

   • To recover the specific binders, inject a finalized concentration of $1 \ \text{mg/mL}$ purified Trypsin solution into the wells, incubating at room temperature for 10 to 15 minutes. The trypsin enzymatically de-adheres the high-affinity binders from the matrix while systematically disabling the infectivity of any co-purified empty helper phage contamination.

   • Collect the eluate promptly, quench the reaction, and add the suspension directly into freshly prepared log-phase E. coli TG1 cells for immediate infective expansion and downstream enrichment rounds.

IV Strategic Research Applications

1. High-Stringency Biopanning of Ultra-Large Human Antibody Repertoires (ScFv / Fab Networks): BioVector? KM13 stands as an internationally recognized gold-standard helper phage system in advanced antibody engineering facilities. It is uniquely prioritized for extracting rare, high-affinity therapeutic candidates out of synthetic or naive human antibody libraries exceeding $10^{10}$ in functional diversity, especially when isolating blocks against toxic, transient, or conserved target antigens.

2. Phage Selection Against Complex Low-Abundance G-Protein Coupled Receptors (GPCRs): Because native multi-pass membrane architectures like GPCRs are notoriously difficult to stabilize and present massive hydrophobic background binding risks, deploying KM13 permits researchers to clean up non-specific passenger artifacts during the elution phase, keeping selection tracks focused purely on true conformation-specific binders.

3. In Vivo Panning of Tissue-Specific Homing Peptides: When injecting peptide libraries directly into animal models to discover organ-specific vascular homing peptides, harvested tissues often yield high background retention. Utilizing the trypsin-cleavable mechanics of KM13 allows for effective post-harvest enzymatic processing, ensuring only high-affinity target-integrated motifs are amplified.

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