Legumain (Recombinant)

Frequently Asked Questions

What molecular weight does recombinant human Legumain run at on SDS-PAGE?

The full-length human Legumain precursor (433 aa, UniProt Q99538) has a predicted molecular weight of ~49 kDa, but the protein undergoes autocatalytic N- and C-terminal trimming to yield the mature active form, which migrates at approximately 36–40 kDa under denaturing conditions. Because this recombinant is expressed in HEK293 cells, N-linked glycosylation adds apparent mass, so the observed band on SDS-PAGE typically runs between 40–47 kDa. Expect diffuse banding if the glycosylation is heterogeneous — this is normal for the native lysosomal form and does not indicate degradation.

What processing forms of Legumain are present in the recombinant preparation and how do they differ?

Legumain is synthesized as a ~56 kDa zymogen (pro-Legumain) that undergoes stepwise autocatalytic processing. The C-terminal prodomain is removed first under mildly acidic conditions, generating an intermediate, followed by N-terminal cleavage to produce the fully mature ~36–40 kDa active enzyme. This recombinant preparation is provided predominantly as the processed, active form. A minor pro-form band at ~49–56 kDa may be visible on SDS-PAGE under reducing conditions. The active site cysteine (Cys189) requires a reducing environment; include 1–5 mM DTT in your assay buffer to maintain full activity.

What substrate should I use for a Legumain fluorogenic activity assay?

The most commonly used fluorogenic substrates for Legumain are Z-Ala-Ala-Asn-NHMec (Z-AAN-NHMec) and Ac-AAVNL-AFC, both of which exploit Legumain's strict asparaginyl-bond specificity. Z-AAN-NHMec (Ex 360 nm / Em 460 nm) is widely preferred for its low background. Use substrate concentrations bracketing the Km (~50–200 µM) for Michaelis-Menten kinetics. Run assays at pH 5.0–5.5 in 50 mM sodium acetate, 1 mM EDTA, 5 mM DTT, 37 °C — the acidic pH is critical for optimal activity and mirrors the lysosomal environment where Legumain is naturally active.

What buffer conditions maximize Legumain enzymatic activity in vitro?

Legumain is a lysosomal protease with a pH optimum between 5.0 and 5.5. For activity assays, use 50 mM sodium acetate pH 5.0, 1 mM EDTA, 5 mM DTT, 0.01% Tween-20. The EDTA chelates trace metal ions that can inhibit the active-site cysteine, and DTT maintains the cysteine in its reduced state. Note that the storage buffer (50 mM Tris-HCl pH 7.5, 150 mM NaCl, 10% glycerol) is deliberately neutral to retard autocatalytic activity during storage — transfer to assay buffer and pre-incubate at 37 °C for 10 minutes before adding substrate to allow full activation.

What starting enzyme concentration should I use for Legumain IC50 inhibitor screening?

For IC50 determination, titrate Legumain in the range of 0.5–5 nM final concentration in your assay well, using Z-AAN-NHMec substrate at or near its Km (~100 µM). At these concentrations, less than 10% substrate conversion should occur at the assay endpoint (typically 30–60 min), which is required for accurate IC50 measurement by the Morrison equation if your inhibitors are tight-binders. Use a 384-well plate format if throughput is a priority. Include E-64 (a pan-cysteine protease inhibitor) as a positive inhibition control to verify enzyme activity in each run.

Can I use recombinant Legumain as a Western blot positive control with the RP-Legumain antibody?

Yes — this recombinant is specifically validated as a positive control for the matched rabbit polyclonal antibody RP-Legumain (/anti-legumain-rabbit-polyclonal-antibody), which was generated from the same expression system. Load 20–50 ng of recombinant Legumain per lane alongside your cell lysate samples. Expect a primary band at 40–47 kDa (mature glycosylated form) and potentially a fainter pro-form band at ~49–56 kDa depending on preparation lot. Using the recombinant and the matched antibody together provides an unambiguous, lot-consistent reference band for antibody validation experiments.

How much recombinant Legumain should I load for Western blot positive control compared to cell lysate?

Load 20–50 ng of recombinant Legumain per lane for a robust signal with RP-Legumain at 1:1,000–1:2,000 primary antibody dilution. This is typically well below the total protein loaded in a cell lysate lane (10–30 µg), so run the recombinant in a dedicated lane rather than mixing it into lysate. Endogenous Legumain expression is highest in kidney, placenta, and monocyte-derived cells — if your cell line expresses low Legumain, the recombinant lane provides a reliable anchor for band identification. Reduce to 10 ng if background is high; increase to 100 ng if using a shorter ECL exposure.

How should I handle and store recombinant Legumain to preserve activity after thawing?

Recombinant Legumain is supplied in 50 mM Tris-HCl pH 7.5, 150 mM NaCl, 10% glycerol as single-use aliquots. Store at -20 °C; do not subject to repeated freeze-thaw cycles, as each cycle can result in significant activity loss for cysteine proteases. After thawing, keep on ice and use within the same working day. If you need to dilute for assay, prepare intermediate stocks in assay buffer (pH 5.0 acetate) containing 0.1% BSA as a carrier to prevent surface adsorption at low concentrations (<10 nM). Validated shelf life is 12 months from date of manufacture when stored correctly.