His Tag Grade Reagents
His Tag Grade Reagents
His tag grade is a product quality and technical standard level defined around the His (polyhistidine) fusion tag and immobilized metal affinity chromatography (IMAC) systems. This grade focuses on recombinant protein expression, affinity purification, and downstream structural/functional studies, where controlled management of metal ions, chelating agents, and related impurities, together with control of key quality attributes of His-tagged recombinant proteins, is used to achieve predictable binding/elution behavior, purity, and reproducibility under defined conditions. Under His tag grade standards, attention is given both to the stability of the chromatography system itself and to the impact of the His tag on target protein conformation, activity, and process compatibility.
I. Basic Scientific Overview of the His Tag
1. Definition and origin
The His tag usually refers to a short peptide consisting of consecutive histidine residues fused to the N-terminus or C-terminus of the target protein by genetic engineering. A sequence of six histidines (6×His) is the most common. Its scientific principle is based on coordination bonds formed between the imidazole side chains of histidine residues and transition metal ions such as Ni²⁺, Co²⁺, Cu²⁺, and Zn²⁺. This property underlies immobilized metal ion affinity chromatography.
2. Core scientific principle
In immobilized metal ion affinity chromatography, chelating ligands (such as iminodiacetic acid or nitrilotriacetic acid) are covalently coupled to the chromatography matrix to chelate transition metal ions, forming a metal-charged stationary phase. When a sample containing His-tagged fusion proteins passes through this medium, the imidazole rings of the histidines in the tag coordinate specifically with the immobilized metal ions, while most host impurity proteins lacking such dense histidine clusters are not retained. Subsequent competitive elution with increasing concentrations of free imidazole in the buffer then allows selective purification of the target protein.
3. Basic properties of the tag
High generality and small size:The His tag consists of only a few amino acids and generally does not significantly alter the structure or function of most proteins, making it broadly applicable to a wide range of targets and expression systems.
Simple purification workflow and mild conditions:IMAC operates under near-neutral conditions with buffers that are compatible with many downstream biochemical and structural studies.
Compatible with multi-step purification:The His tag can be combined in sequence with ion-exchange chromatography, size-exclusion chromatography, and other methods to further improve final product purity and homogeneity.
Usable for detection and capture:Under appropriate configurations, the His tag can also be used for immobilization, activity assays, and surface display, serving as a basic tag that supports both enrichment and functional applications.
II. Definition and Features of His Tag Grade Reagents
1. Definition
A dedicated quality grade for His tag–related applications, covering both reagents used for the expression and purification of His-tag fusion proteins and recombinant proteins bearing a His tag. For reagents, critical impurities such as metal ions are strictly controlled to ensure stable and reproducible immobilized metal affinity chromatography and consistent binding/elution of His-tagged proteins. For recombinant proteins, the presence of the structural His tag is ensured and key quality attributes such as purity and biological activity are controlled, with detailed specifications defined in the Certificate of Analysis (COA) for each product.
2. Product features
(1) Suitable for metal chelate chromatography systems
Key impurities such as metal ions and chelating agents are controlled within defined limits in the formulation, so that His-tagged fusion proteins exhibit relatively stable and predictable binding and elution behavior under standard Ni²⁺/Co²⁺ chelate conditions.
(2) Supporting quality control of His-tagged recombinant proteins
Recombinant proteins carrying His tags have clearly defined tag information at the sequence level, and are tested against specified criteria such as purity, biological activity (where applicable), and impurity residues. The corresponding data are documented in the CoA.
(3) Emphasis on batch-to-batch performance consistency
Key performance parameters related to the His tag are monitored and recorded across different batches to ensure the reproducibility and traceability of metal chelate chromatography and downstream applications of recombinant proteins.
III. Key Quality Attributes
Control dimension | Quality requirements | Analytical methods | Technical significance |
Metal ions and chelators background | Levels of critical metal ions and chelators are kept within defined ranges to avoid excessive interference | Metal content determination (e.g., ICP); impurity analysis | Ensures stable loading of metal-chelate media and robust His–metal coordination |
Affinity medium capacity and stability | Metal loading and effective binding capacity show controlled batch-to-batch variation, with stable performance upon reuse | Binding-capacity measurements; multi-cycle chromatography performance evaluation | Improves predictability of binding/elution behavior and overall method reproducibility |
Binding and elution characteristics | Exhibits a well-defined binding window and elution profile under recommended buffer conditions | Imidazole gradient elution tests; pH-gradient evaluation | Facilitates development of gradient or isocratic elution methods and supports scale-up applications |
Impurities and nonspecific binding | Nonspecific adsorption and co-eluting impurities are maintained within acceptable limits | SDS-PAGE; host cell protein / nucleic acid residual testing | Increases purity and signal-to-noise ratio, reducing interference in downstream analyses |
Recombinant protein purity and activity | His-tagged recombinant proteins meet specified purity criteria, with activity maintained within an appropriate range | HPLC/SEC; functional assays (where applicable) | Provides suitable material for structural studies, functional assays, and process development |
Batch consistency and documentation traceability | Key parameters remain within predefined variation ranges across batches, with fully traceable documentation | Inter-batch comparison tests; quality summaries and CoA records | Supports long-term studies, multi-center comparisons, and robust method transfer |
IV. Typical Application Scenarios
4.1 Affinity purification of recombinant proteins
(1) General affinity chromatography step
After expression of His-tagged fusion proteins, metal chelate affinity chromatography is used to achieve one-step affinity capture and initial purification, providing a concentrated starting material for subsequent ion-exchange, hydrophobic interaction, or size-exclusion chromatography.
(2) Scale-up from small-scale to larger processes
Affinity conditions established at small scale under the His tag grade framework can be scaled up to larger volumes under the same or similar buffer systems and linear flow rates, providing foundational data for process scale-up and validation.
4.2 Structural biology and process development
(1) Structural biology sample preparation
The His tag is commonly used in the front-end preparation of samples for structural studies such as X-ray crystallography, cryo-EM, and NMR. Within a His tag grade system, relatively stable, initially purified samples can be obtained and, when combined with downstream polishing steps, can meet the high homogeneity requirements of structural biology.
(2) Process development and method transfer
During process development, His tag grade media and buffer systems are used to explore parameters such as pH, ionic strength, and imidazole gradients. This provides reproducible groundwork for subsequent process locking and analytical method transfer.
4.3 Analytical methods and quantitative applications
(1) Monitoring of expression and purification
Using the His tag as a unified detection handle, SDS-PAGE or immunodetection can be performed at each stage of expression, lysis, loading, flow-through, and elution to monitor process yield and impurity clearance efficiency.
(2) Quantitative or semi-quantitative analysis
Within appropriate standards and linear ranges, the expression level or recovery of His-tagged fusion proteins can be relatively quantified using chromatographic peak areas, Western blot signals, or ELISA readouts.
V. Advantages of Aladdin Products
(1) Metal-chelating media and buffer recommendations
Provide chelating affinity media suitable for Ni²⁺, Co²⁺ and other metal ions, and include recommended ranges for binding, wash, elution and regeneration conditions in the instructions, serving as a starting point for designing purification workflows for His-tagged fusion proteins.
(2) Supporting tools for expression and detection
Provide relevant expression vectors and detection reagents such as anti-His antibodies for His-tagged expression, together with basic usage instructions, to facilitate expression assessment, band verification and in-process monitoring.
(3) Recombinant protein specifications and quality information
For selected His-tagged recombinant proteins, provide purity, activity (where applicable) and basic batch information as specified in the CoA, enabling their use in method development, control experiments and standard curve construction.
VI. Comparison with Reagents of Similar Grade
Comparison dimension | His tag grade | GST tag grade | Strep II tag grade | FLAG tag grade |
Core principle | Histidine–metal ion coordination | Glutathione S-transferase binding to its substrate | Engineered peptide binding to an engineered streptavidin variant | Short peptide binding to a high-specificity monoclonal antibody |
Tag size | Very small (<1 kDa) | Large (~26 kDa) | Small (~1 kDa) | Small (~1 kDa) |
Binding/elution conditions | Broadly tolerant; typically imidazole competition or low-pH elution | Mild; elution by reduced glutathione competition | Mildest; elution by biotin analog competition under near-physiological conditions | Mild; elution with low pH or competitive FLAG peptide |
Product purity (one-step) | Moderate; requires optimized wash conditions | Moderate; GST dimerization may introduce additional species | Very high; extremely low background binding | High; high antibody specificity |
Product cleanliness | Contains imidazole/metal ions; desalting is often required | Contains reduced glutathione | Very high; no interfering compounds | Elution peptide can be removed; clean background |
Tolerance to harsh conditions | ★★★★★ (tolerates denaturants and detergents) | ★★☆☆☆ (prone to loss of activity) | ★★☆☆☆ (requires mild conditions) | ★★☆☆☆ (requires mild conditions) |
Main advantages | Robust, general, low cost, tolerant of denaturation, easy to scale up | Can enhance solubility of proteins expressed in prokaryotes; convenient for GST pull-down | Top-tier purity and specificity under native conditions; extremely mild conditions | Extremely high detection sensitivity and specificity; tag can be easily removed |
Considerations | Residual metal ions; nonspecific binding requires optimization | Large tag may affect structure/function; tag removal can be difficult | Relatively high cost; highly sensitive to trace biotin | Relatively high cost; mainly used for detection and mild purification |
Typical first-choice scenarios | 1. Initial capture and rapid preparation. 2. Purification of inclusion body or membrane proteins. 3. High-throughput screening and large-scale production. | 1. Improving solubility in prokaryotic expression. 2. Protein interaction studies (pull-down). | 1. Structural biology sample preparation. 2. Functional studies requiring extreme purity and native conditions. | 1. High-sensitivity immunodetection. 2. Immunoprecipitation requiring mild competitive elution. |
VII. Representative Aladdin Products
Catalog No. | Product Name | Grade and Purity |
Recombinant Protein A-Cys, His | Animal Free，Carrier Free，His-Tag，≥96%，(SDS-PAGE&RP-HPLC) | |
Recombinant Human Histamine N-Methyltransferase/HNMT Protein | Carrier Free，His-Tag，≥90%(SDS-PAGE)，See COA | |
Recombinant Human Histone H3 Protein | Carrier Free，Azide Free，His-Tag，≥90%(SDS-PAGE) | |
Recombinant Human Histone H2AX Protein | Carrier Free，Azide Free，His-Tag，≥90%(SDS-PAGE) | |
Recombinant Human Histone H2B Protein | Carrier Free，Azide Free，His-Tag，≥95%(SDS-PAGE) | |
Recombinant Human Histone H4 Protein | Carrier Free，Azide Free，His-Tag，≥90%(SDS-PAGE) | |
Nogapendekin alfa | Animal Free，Carrier Free，Bioactive，ActiBioPure™，Moligand™，His-Tag，≥98%(SDS-PAGE) | |
Recombinant Protein G | Animal Free，Carrier Free，GMP，His-Tag，≥90%(SDS-PAGE)，See COA | |
Recombinant Protein L (N-His, C-Cys) | Animal Free，Carrier Free，His-Tag，≥96%(SDS-PAGE) | |
Recombinant Protein A/G (C-His) | Animal Free，Carrier Free，His-Tag，≥96%，(SDS-PAGE&RP-HPLC) | |
Mussel Adhesive Proteins | Animal Free，Carrier Free，sterile-filtered，Suitable for molecular biology，His-Tag，≥90%(SDS-PAGE)，DL-DOPA:≥3% | |
Recombinant Porcine Trypsin | Animal Free，Carrier Free，Bioactive，sterile-filtered，ActiBioPure™，Suitable for molecular biology，EnzymoPure™，His-Tag，≥90%，>10000 U/mg | |
Recombinant Canine CD8 Protein | Animal Free，Carrier Free，His-Tag，Fc-Tag，≥90%(SDS-PAGE)，See COA |
Among the various tag-grade systems, His tag grade is more oriented toward serving as a “universal affinity entry point” for recombinant protein preparation, leveraging a well-established immobilized metal affinity chromatography (IMAC) platform to provide a relatively standardized capture and initial purification route across diverse proteins and expression hosts. Compared with Strep II tag grade, which emphasizes polishing under native conditions; GST and MBP tag grades, which combine solubility enhancement with affinity purification; and SUMO tag grade, which focuses on removable solubility enhancement, His tag grade is characterized by its mature processes, relatively high binding capacity, and broad applicability.