Anti-Calpain Small Subunit 1 Rabbit Polyclonal Antibody

Frequently Asked Questions

What molecular weight band should I expect for CAPNS1 on Western blot?

CAPNS1 migrates at approximately 28 kDa on SDS-PAGE, corresponding to its 268-amino acid sequence. You may observe the band slightly above the predicted mass depending on gel percentage and running conditions. The small subunit runs well-separated from the catalytic large subunits CAPN1 (80 kDa) and CAPN2 (80 kDa), making identification straightforward in whole cell lysates. If you are working with tissue samples where calpain is abundant, you should see a single clean band at 28 kDa with minimal background at the recommended 1:1000 dilution.

Does this antibody detect both mu-calpain and m-calpain complexes?

Yes. CAPNS1 is the common regulatory subunit shared by both μ-calpain (CAPN1/CAPNS1 heterodimer) and m-calpain (CAPN2/CAPNS1 heterodimer). This antibody detects CAPNS1 regardless of which catalytic subunit it associates with, so it reports total small subunit expression rather than distinguishing between the two calpain isoforms. If you need to differentiate μ- versus m-calpain activity or localization, you will need separate antibodies against CAPN1 or CAPN2. Co-immunoprecipitation experiments can confirm complex formation if that is your experimental goal.

What dilution should I start with for Western blot of CAPNS1?

Start at 1:1000 in your blocking buffer for overnight incubation at 4°C or 1-2 hours at room temperature. CAPNS1 is typically expressed at moderate to high levels in most cell types, so this dilution provides a good signal-to-noise ratio without excessive background. If your signal is weak in low-abundance samples such as certain differentiated primary cells, you can increase concentration to 1:500. Conversely, in calpain-rich tissues like skeletal muscle or brain lysates, 1:2000 may suffice. Always titrate against your specific sample type and detection system.

Is this antibody validated in mouse or rat samples?

This antibody has been validated in human samples. Mouse and rat CAPNS1 share approximately 95-97% sequence identity with human CAPNS1, so cross-reactivity is likely but not experimentally confirmed by us. If you are working with rodent samples, we recommend treating this as predicted reactivity and including a positive control such as HeLa or HEK293 lysate alongside your experimental samples on the same blot. Many researchers have successfully used human CAPNS1 antibodies in mouse and rat, but you should verify band specificity at 28 kDa in your system.

What controls should I include when blotting for CAPNS1?

Include a positive control lysate from a human cell line such as HeLa, Jurkat, or HEK293, where CAPNS1 is constitutively expressed. For a negative control, consider lysate from cells treated with CAPNS1 siRNA or CRISPR knockout if available, though wildtype versus treated comparisons are usually sufficient. Loading controls such as beta-actin or GAPDH are essential since CAPNS1 levels can vary with cell density and calcium signaling status. If investigating calcium-dependent translocation, fractionate cytosolic and membrane fractions and blot separately; CAPNS1 should shift to membrane fractions upon calcium stimulation.

Can I use this antibody for immunofluorescence of CAPNS1?

Triple Point Biologics antibodies are routinely validated for immunofluorescence applications in addition to Western blot. For CAPNS1, start with a 1:100 to 1:200 dilution for IF. You should observe diffuse cytoplasmic staining under basal conditions, with potential enrichment at the plasma membrane or focal adhesions upon calcium ionophore treatment such as A23187 or ionomycin. Methanol fixation at -20°C often gives cleaner staining for cytoplasmic proteases than paraformaldehyde. Include a no-primary-antibody control to assess non-specific secondary binding, particularly in cells with high autofluorescence.

How should I store this Calpain-S1 antibody and what is the shelf life?

Store at -20°C in the supplied glycerol-based buffer. Avoid repeated freeze-thaw cycles by making single-use aliquots if you use the antibody infrequently. Under these conditions, the antibody remains stable for at least 12 months from date of receipt. If you notice increased background or diminished signal over time, this typically indicates degradation or contamination. Do not store diluted antibody in blocking buffer for more than one week at 4°C. For long-term storage beyond one year, -80°C is preferable, though most labs find -20°C adequate for routine use.

Does calcium in my lysis buffer affect CAPNS1 detection?

CAPNS1 itself remains detectable regardless of calcium concentration, but be aware that active calpain will proteolyze many substrates if calcium is present during lysis. Use EDTA or EGTA-containing lysis buffers (1-5 mM) to chelate calcium and prevent artifactual proteolysis during sample preparation. Some protocols also include calpain inhibitors such as calpeptin or MDL28170 as an extra precaution. If you are specifically studying calcium-dependent calpain activation or autolysis, include calcium and collect samples rapidly on ice, then compare CAPNS1 levels and cleavage products between calcium-treated and chelator-treated lysates.