Calpain S-2 (Recombinant)

Frequently Asked Questions

What molecular weight band should Calpain S-2 (Recombinant) run at on SDS-PAGE and Western blot?

The full-length CAPNS2 polypeptide is 248 amino acids with a calculated molecular weight of ~28 kDa. On reducing SDS-PAGE, the recombinant produced in HEK293 cells typically migrates at approximately 30–32 kDa due to mammalian glycosylation and post-translational modifications. On Western blot using our matched antibody RP-CalpainS2, expect a single predominant band in that range. Anomalous migration slightly above predicted MW is common for this subunit and is not indicative of degradation or impurity. Purity is confirmed >90% by silver-stained SDS-PAGE.

Is Calpain S-2 (Recombinant) the same isoform as CAPNS1, and what distinguishes it functionally?

No — CAPNS2 (UniProt Q96L46) is a paralog of the ubiquitously expressed small subunit CAPNS1, sharing the same domain architecture but displaying a more restricted tissue distribution. Unlike CAPNS1, CAPNS2 is considered a candidate tissue-specific chaperone for cognate large catalytic calpain subunits. This recombinant is produced as the full-length 248-aa CAPNS2 sequence and has not been truncated or domain-swapped. Researchers working on tissue-specific calpain complexes or comparing small-subunit isoform function should ensure they are not substituting CAPNS1 reagents for CAPNS2 — the two are not functionally interchangeable in all contexts.

What substrates and assay formats are recommended for measuring Calpain S-2 (Recombinant) proteolytic activity?

As a regulatory small subunit, CAPNS2 itself does not carry the catalytic cysteine — proteolytic activity requires reconstitution with a cognate large catalytic subunit (e.g., calpain-1 or calpain-2 heavy chain). To measure activity of reconstituted complexes, fluorogenic peptide substrates such as Suc-LLVY-AMC or Z-Leu-Arg-AMC (ex/em 380/460 nm) are standard. Assays should be run in the presence of 0.5–5 mM CaCl₂ in 50 mM Tris-HCl pH 7.5, 150 mM NaCl. Include a no-calcium control to confirm calcium-dependence. Starting complex concentration of 50–200 nM is typical for initial titration.

What buffer conditions should I use for Calpain S-2 (Recombinant) activity assays or protein-protein interaction studies?

The protein is shipped in 50 mM Tris-HCl pH 7.5, 150 mM NaCl, 10% glycerol — this storage buffer is compatible with most downstream assays without prior exchange. For calcium-dependent activity assays with a reconstituted large subunit, supplement with 0.5–5 mM CaCl₂ and 2 mM DTT to maintain cysteine protease activity. For pull-down or SPR binding studies of subunit–subunit interactions, dilute into the same base buffer supplemented with 0.05% Tween-20 and 1 mg/mL BSA to reduce nonspecific binding. Avoid EDTA-containing buffers, which will chelate calcium and abolish activity.

What starting concentration of Calpain S-2 (Recombinant) is recommended for reconstitution and dose-response experiments?

For reconstitution with a large catalytic calpain subunit, begin with equimolar small-to-large subunit ratios at 100–500 nM total protein and titrate based on measured substrate turnover. For inhibitor IC₅₀ determination in reconstituted complex assays, use the lowest enzyme concentration that gives a robust, linear signal window — typically 50–150 nM complex — to avoid enzyme excess artifacts that artificially elevate apparent IC₅₀. For Western blot positive controls, 50–200 ng loaded per lane is sufficient for detection with the matched RP-CalpainS2 antibody without saturating the signal.

Can I use Calpain S-2 (Recombinant) as a positive control for Western blot with the RP-CalpainS2 antibody?

Yes — this is one of the primary intended uses of pairing REC-CalpainS2 with the matched rabbit polyclonal RP-CalpainS2. Load 50–200 ng of recombinant per lane on a 12–15% SDS-PAGE gel under reducing conditions. The antibody (see /anti-calpain-s2-rabbit-polyclonal-antibody) is validated for Western blot and should resolve a clean band at ~30–32 kDa. This pairing also serves as a system-level positive control when validating RP-CalpainS2 for detection of endogenous CAPNS2 in tissue lysates, confirming both antibody reactivity and correct band assignment before committing to immunoprecipitation or IHC workflows.

How much Calpain S-2 (Recombinant) should I load for antibody validation Western blot alongside cell lysate?

Load 50–100 ng of REC-CalpainS2 in a dedicated lane adjacent to your cell or tissue lysate. At this amount, the RP-CalpainS2 rabbit polyclonal antibody provides a strong reference band at ~30–32 kDa under standard ECL detection. Running the recombinant alongside endogenous samples lets you confirm co-migration of the endogenous band with the recombinant standard — an important control given that CAPNS2 tissue distribution is restricted and endogenous signal strength varies considerably by cell type. Avoid loading more than 200 ng per lane, as signal saturation can obscure the comparison.

How should I store and handle Calpain S-2 (Recombinant) to maintain stability and avoid activity loss?

Store at −20°C in the single-use aliquots provided. The formulation in 50 mM Tris-HCl pH 7.5, 150 mM NaCl, 10% glycerol is designed to maintain protein integrity through the freeze-thaw cycle, but repeated freeze-thaw significantly degrades both structural integrity and subunit-interaction capacity — do not refreeze thawed aliquots. On ice, the thawed protein is stable for 4–8 hours for same-day experiments. If longer bench stability is required, supplement with 0.1% BSA as a carrier. Endotoxin is confirmed <0.1 EU/µg by LAL assay, so no additional depyrogenation step is needed for cell-based assays.