Western Blot — Metalloproteinases

Metalloproteinases in humans span three major families: matrix metalloproteinases (MMPs, 23 members), ADAM (a disintegrin and metalloproteinase, ~22 members), and ADAMTS (a disintegrin and metalloproteinase with thrombospondin motifs, 19 members). All share a zinc-dependent catalytic mechanism with the conserved HEXXHXXGXXH zinc-binding motif in the catalytic domain, and all are synthesised as latent proenzymes that require propeptide removal (the "cysteine switch" activation) to become active.

This protocol covers Western blot detection of metalloproteinases with Triple Point rabbit polyclonal antibodies. Standard mechanics are covered elsewhere; this document focuses on the specific adjustments required for metalloproteinase-specific biochemistry.

Sample preparation — zinc chelators and activation state

The single most consequential decision for a metalloproteinase Western blot is what to do about EDTA in the lysis buffer. EDTA at 1-5 mM is a standard component of most protease inhibitor cocktails and RIPA-like buffers — but it chelates the active-site zinc of MMPs, ADAMs, and ADAMTS proteinases, inactivating them irreversibly at high concentrations.

For Western blot detection without downstream activity assay, this does not matter — you are detecting protein, not activity, and EDTA-inactivated enzyme is still fully immunodetectable. In fact, EDTA is a mild pro-metalloproteinase inhibitor cocktail component precisely because it prevents autoproteolysis during lysis.

For Western blot detection with downstream activity assay or zymography, EDTA must be omitted or replaced. The buffer choices split into three cases:

Expected molecular weights — latent vs active

Every metalloproteinase runs at both a latent (proenzyme) and active MW. The MW difference is ~10 kDa for most MMPs (the mass of the propeptide) and 25-50 kDa for ADAMs/ADAMTS (which have larger prodomains).

Gel conditions — reducing vs non-reducing, and zymography compatibility

Standard reducing SDS-PAGE (Laemmli buffer with 5% β-mercaptoethanol or 100 mM DTT, boiled at 95°C for 5-10 minutes) is the default for all metalloproteinase Western blots.

Non-reducing gels are used specifically for:

• Gelatin zymography (MMP-2 and MMP-9): substrate-embedded gels run under non-reducing, non-denaturing conditions, then renatured to detect enzymatic activity by substrate degradation.
• MMP-9 dimer visualisation: MMP-9 forms a disulfide-linked homodimer at ~180 kDa; this is visible only under non-reducing conditions and collapses to monomer on reduction.
• MMP-TIMP complex visualisation: some MMP-TIMP complexes are SDS-stable but reduction-sensitive; non-reducing conditions preserve them.

Running the same sample on both reducing and non-reducing gels can reveal complex formation and dimerisation patterns that reducing gels hide. This is a specific advantage for MMP-9 and MMP-2 investigations.

Blocking and antibody incubation

Standard 5% non-fat dry milk in TBS-T (0.1% Tween-20). Triple Point metalloproteinase antibodies are supplied for use at 1:1,000 to 1:5,000 per CoA. Overnight primary incubation at 4°C. Anti-rabbit HRP secondary at 1:10,000.

ECL detection with enhanced substrate (Dura or equivalent) is recommended for endogenous MMPs in most cell lines, which express at moderate levels. Femto-scale ECL is warranted only for low-expression tissues or primary cell types.

Detection strategies for specific questions

"Is this MMP activated?"

Two orthogonal approaches:

• Propeptide + catalytic domain antibody pair. Propeptide antibody detects only the proenzyme (~10 kDa higher MW). Catalytic-domain antibody detects both proenzyme and mature. Loss of propeptide signal with retention of a lower-MW catalytic-domain band = activation.
• Gelatin zymography. For MMP-2 and MMP-9 specifically, zymography directly reports enzymatic activity. Latent forms show weaker activity on zymography than mature forms (the propeptide has been removed by SDS during electrophoresis, permitting some activity). Zymography intensity + Western blot band intensity together resolve activation state.

"Is this membrane-anchored metalloproteinase shed?"

Membrane-type MMPs (MMP-14, -15, -16, -17, -24, -25) and most ADAM family members are membrane-anchored, and shedding of the ectodomain is a regulated event. Probe cell lysate and conditioned media with paired catalytic-domain and C-terminal / cytoplasmic-tail antibodies:

• Cell lysate: both antibodies detect the intact membrane-anchored form.
• Conditioned media: only the catalytic-domain antibody detects the shed ectodomain; the C-terminal antibody signal is absent from the media.

Absence of C-terminal signal from the media confirms that the media form is truly shed and not the result of cell lysis contamination.

"Is this MMP TIMP-bound?"

TIMP-1 preferentially inhibits MMP-9; TIMP-2 preferentially inhibits MMP-2 (and paradoxically also participates in MMP-2 activation via MMP-14); TIMP-3 inhibits ADAM17 and other membrane MMPs. TIMP-bound MMP runs as a higher-MW SDS-stable complex (~30 kDa higher than free enzyme). Under reducing conditions, most TIMP-MMP complexes dissociate, but some (particularly TIMP-1-MMP-9) are stable enough to survive reduction. If you observe a persistent high-MW smear above the expected proenzyme band, TIMP complex is a plausible explanation. Confirm by running an untreated aliquot alongside one boiled with 1 M urea + 5% SDS at 100°C for 15 minutes — harsher denaturation dissociates the complex.

Superpooled kits for metalloproteinases

Triple Point Superpooled kits are available for the major MMPs (MMP-1, -2, -3, -7, -9, -13, -14) and for the highest-priority ADAMs (ADAM10, ADAM17, ADAMTS4, ADAMTS5). Each kit includes propeptide, catalytic-domain, and hemopexin/C-terminal-directed antibodies as separate reagents, plus a kit-level datasheet showing the expected multi-band pattern including latent, active, and (where relevant) shed forms. See the SPA method overview and usage protocol for detail.

Common failure modes specific to metalloproteinases

All bands missing after long lysate storage

Metalloproteinases autoproteolysed during storage. The enzyme, even in EDTA buffer, can very slowly cleave itself. Store lysate at −80°C in single-use aliquots, not at −20°C or 4°C.

MMP-9 dimer confused with degradation smear

MMP-9 homodimer at ~180 kDa on non-reducing gels can look like a degradation smear. Confirm by running reducing vs non-reducing side-by-side — the 180 kDa band should collapse to 92 kDa on reduction. If it persists on reduction, it is aggregation, not physiological dimer.

Cross-detection between MMP-2 and MMP-9 by catalytic-domain antibodies

The two gelatinases share ~50% catalytic-domain identity. Antibodies raised against unselected catalytic peptides commonly cross-detect. Use Triple Point's paralogue-specific antibodies or run adjacent lanes with paralogue-specific detection to distinguish. See MMP-9 vs MMP-2 selection guide.

ADAM10 shedding lost when using strong lysis

Some cell fractionation protocols use pH shifts or high-salt buffers that release shed ADAM10 back into the cell fraction. If you are studying shedding, use minimal-perturbation media collection (fresh serum-free media over cells for 4-24 hours, collected without cell disruption) rather than lysing cells to obtain "media."

MT1-MMP autoprocessing to inactive 45 kDa fragment

MT1-MMP autoprocesses to a catalytically inactive 45 kDa form as a regulatory feedback. This is not degradation — it is normal biology. If you see a 45 kDa band on MT1-MMP blots in addition to the 66 kDa pro and 60 kDa active forms, it is likely the autoprocessed regulatory form.

Positive control samples for metalloproteinases

Related

• MMP antibody catalog
• MMP family antibody selection
• MMP-9 vs MMP-2 selection
• MMP-1 vs MMP-13 selection
• ADAM10 vs ADAM17 selection
• TIMP-1 vs TIMP-2 selection
• The Superpooled (SPA) method
• Dilution optimization
• Controls and validation
• IP protocol for proteinase enrichment
• Zymogens and proenzymes overview