Tau (K18) Wild-Type Pre-formed Fibrils

What it means: Target is the identity of the recombinant protein you’re purchasing. The target listed on this page is Tau.

How to interpret here: Use Tau as your primary “construct match” checkpoint—confirm it is the exact protein/isoform you need for your antibody validation, binding study, or assay standard. The sequence origin is Human, which matters when antibodies or receptors are species‑specific. The protein length is 141 amino acids, which indicates whether you’re getting full‑length protein or a construct. The expression system is E. coli, which can affect folding and post‑translational modifications. Choose this when target + origin + construct match your application; consider a different construct if you need a specific domain, tag‑free format, or native PTMs.

Why it matters for buying:

• Binding and specificity: Different isoforms, fragments, or closely related family members can change antibody/ligand binding.
• Functional relevance: A fragment may be ideal for epitope mapping but may not reproduce full‑length conformation or activity.
• Reproducibility: Documented construct details (origin, length/region, expression system) reduce surprises between experiments and batches.

Helpful selection notes for this listing:

• Synonyms: Tau, Microtubule-associated Tau, Microtubule-associated protein Tau, MAPT, MAP, Tau-441.

Practical guidance:

• Confirm your epitope/domain: If you have an antibody epitope map or domain requirement, verify it is present in the construct (length/region).
• Plan controls: Include an unrelated protein control (and, when possible, a known‑binding antibody/ligand) to detect non‑specific binding.
• Pilot before scaling: For critical assays, test a small amount first to confirm binding/activity under your exact buffer and immobilization conditions.

What to watch out for:

• PTM‑dependent binding: If your antibody/ligand requires glycosylation or native folding, confirm the expression system supports it.
• Tag or fusion effects: If a tag is present, it can change binding or introduce background—use tag controls when needed.
• Assay standard fit: For quantitative standards, confirm the standard curve behavior in your matrix and avoid relying on concentration claims without lot documentation.

What it means: Species refers to the organism the protein sequence is derived from. The value on this page is Human.

How to interpret here: Use Human to decide if this protein matches the biology you’re studying and the reagents you plan to use. This listing is for Tau derived from Human. Choose this when your antibody/ligand is expected to recognize this origin; validate when using it to test cross‑reactivity across species.

Why it matters for buying:

• Epitope differences: Small sequence changes across species can dramatically alter antibody binding.
• Interpretation of binding: A “negative” result with one species protein may reflect sequence mismatch rather than true lack of binding.
• Translational relevance: If your end goal is human biology, using the human origin protein reduces ambiguity.

Practical guidance:

• Check reagent docs: Compare the immunogen/epitope or binding region in your antibody datasheet against the species shown here.
• Cross‑species panels: For cross‑reactivity work, test multiple ortholog proteins under identical conditions with proper controls.
• Record construct details: Include species + length/region + expression system in your methods for reproducibility.

What to watch out for:

• Species vs expression host: Species here describes sequence origin, not the expression host (see Expression System).
• Variant coverage: If sequence variants/isoforms matter (pathogens or polymorphic proteins), confirm the exact construct details in the datasheet.

What it means: Expression System is the host used to produce the recombinant protein. The expression system listed here is E. coli.

How to interpret here: Use E. coli to anticipate folding and post‑translational modifications (PTMs), and to judge whether the protein will behave “native‑like” in your assay. Bacterial expression typically lacks mammalian glycosylation and some native PTMs—this can matter for PTM‑dependent antibodies or receptor binding. For Tau, choose the expression host that best matches your question (native PTMs vs rapid bacterial production). Choose this when the host is compatible with your binding/functional needs; consider mammalian/insect expression if native conformation/PTMs are critical.

Why it matters for buying:

• PTMs and conformation: Host selection influences glycosylation, disulfide bonding, and folding—key for many epitopes and receptors.
• Impurity profile: Different hosts introduce different impurities; bacterial systems can also carry endotoxin that matters for cell-based work.
• Assay reproducibility: Using the same expression system across studies improves comparability.

Practical guidance:

• Validate early: Confirm binding/activity with your specific antibody/ligand in a small pilot.
• Choose buffers intentionally: Some hosts produce proteins that are more prone to aggregation—follow recommended storage and reconstitution guidance.

What to watch out for:

• Glycosylation-sensitive binding: Lack of glycosylation can reduce binding for certain antibodies and receptors.
• Aggregation: Reconstitute gently and avoid repeated freeze–thaw; aliquot after reconstitution where possible.
• “Activity” assumptions: Host choice can affect activity—confirm activity is provided/validated if you need functional protein.

What it means: Conjugate(s) describes whether this protein is supplied with a modification (a tag or labeling chemistry) that changes how you capture, detect, or handle it. The value shown here is No Tag.

How to interpret here: Treat No Tag as your workflow selector—choose it based on how you plan to immobilize the protein (capture surfaces, beads), detect it (fluorescence/streptavidin/anti‑tag), and what background/interference you can tolerate. This listing is for Tau (Human origin). Pair this with expression system (E. coli) when folding/PTMs could affect binding. No Tag indicates a tag‑free preparation—use this when you want the most native‑like construct and you don’t need tag‑based capture.

Why it matters for buying:

• Capture strategy: Tags/conjugates enable oriented immobilization (often more reproducible than passive adsorption).
• Detection and background: Added chemistries expand readout options but also add extra binding sites and background risks.
• Workflow compatibility: Your assay (pull‑downs, BLI/SPR, fluorescence readouts) may depend on having the right conjugate.

Practical guidance:

• Immobilization choice: Without a tag, passive adsorption or chemical coupling may be used—pilot test to confirm binding/activity is preserved.
• Plan controls: Include an unrelated protein with the same conjugate (or a tag/dye control) to identify conjugate‑driven background.
• Prefer oriented capture when possible: Biotin/His/other tags can improve reproducibility versus random plate coating.

What to watch out for:

• Interference with binding: Tags/conjugates near an epitope can reduce binding—if results look off, compare to a tag‑free construct.
• Non‑specific interactions: Some labels increase stickiness to plastics—use low‑bind tubes and blockers as appropriate.
• Assuming removability: Do not assume a tag can be cleaved unless a protocol is provided.

What it means: Purity describes how clean the protein preparation is (often estimated by SDS‑PAGE or chromatography). The purity stated here is > 95%.

How to interpret here: Use > 95% to judge whether the preparation is suitable for your assay’s sensitivity and background tolerance. Choose this when the purity level fits your use-case; consider higher purity/low endotoxin options for quantitative standards, kinetics, or cell-based work.

Why it matters for buying:

• Background signal: Impurities can increase non-specific binding in ELISA coating and surface binding assays.
• Lot-to-lot consistency: Higher purity often reduces variability in sensitive applications.
• Biological confounding: Contaminants (including endotoxin) can produce effects unrelated to your target.

Practical guidance:

• Match purity to application: Screening assays may tolerate lower purity; quantitative standards and kinetics benefit from cleaner prep.
• Quick QC: For critical work, verify band size and major species by SDS‑PAGE/Western on arrival.
• Use controls: Include buffer-only and unrelated protein controls to detect non-specific background.

What to watch out for:

• Purity method differences: SDS‑PAGE estimates are not the same as “single molecular species.”
• Aggregates: Purity does not always report aggregation—inspect solubility and consider running non-reducing gels if relevant.
• Cell-based assays: If you see unexpected inflammatory responses, consider endotoxin and validate with controls.

What it means: Protein Length indicates whether the protein is full-length or a construct/fragment. The value listed here is 141 amino acids.

How to interpret here: Use 141 amino acids to confirm the construct matches your assay design. For Tau, full-length constructs are often preferred for functional or conformational binding, while fragments can be ideal for epitope mapping. Choose this when the construct supports your binding/function needs; consider another length/region if you require specific domains, termini, or native conformation.

Why it matters for buying:

• Epitope coverage: Antibodies raised to one domain may not bind constructs missing that region.
• Conformation and activity: Fragments may not reproduce full-length folding, oligomerization, or functional interfaces.
• Assay background: Smaller constructs can reduce non-specific interactions in some binding assays.

Practical guidance:

• Map your binding region: If you know the epitope/domain, confirm it overlaps the construct.
• Confirm expected size: Use length + molecular weight (if provided) to verify SDS‑PAGE band size.
• Validate with an orthogonal method: For critical decisions, confirm binding/function with a second assay (Western, BLI/SPR, activity assay).

What to watch out for:

• Signal peptide/transmembrane removal: Many constructs exclude these regions; that can be normal but may change conformation.
• PTM-dependent epitopes: A full-length protein expressed in bacteria may still lack native PTMs.
• Assuming “full length” equals “native”: Expression system and buffer still influence how native-like the protein is.