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- Table of Contents
COMP · Western blot design guide
Design a Western Blot for COMP
Real validated COMP Western blot protocols, expected-band and isoform facts, troubleshooting for weak or shifted signal, and recommended anti-COMP WB antibodies. Everything you need to plan the experiment before you commit precious samples.
Last reviewed: May 2026 · Scientific review: Boster Bio technical team
COMP Western Blot Experimental Design Guide
Expected bands, validated protocols, controls and antibodies — the at-a-glance facts below, then the full design guide.
Must know before running
| Expected band | ~82.9 kDa | |
| Observed band | 110 kDa | |
| Gel | 8–10% | |
| Negative control | siRNA / KO lysate |
Important caveats
Reasons your observed band may differ from the expected size.
| PTM | Glycosylated + Cleaved | |
| Caveat | N-glycosylation | |
| Regulation | Coagulation | |
| Isoform | 2 isoform(s) |
Section 1
Real Curated COMP Western Blot Protocols
Literature-validated Western blot parameters for COMP — gel percentage, transfer, blocking, antibody incubation and detection, extracted from published methods.
| Sample / lysate | human HepG2 , Lane 2: human Hacat , Lane 3: human CACO-2 , Lane 4: human 293T , Lane 5: rat cartilage , Lane 6: mouse cartilage . After electrophoresis, proteins were transferred to a nitrocellulose membrane at 150 mA for 50-90 minutes. Blocked the membrane with 5% non-fat milk/TBS for 1.5 hour at RT. The membrane was incubated with rabbit anti-COMP antigen affinity purified polyclonal antibody (Catalog # A02443-1) at 0.5 μg/mL overnight at 4°C, then washed with TBS-0.1%Tween 3 times with 5 minutes each and probed with a goat anti-rabbit IgG-HRP secondary antibody at a dilution of 1:5000 for 1.5 hour at RT. The signal is developed using an Enhanced Chemiluminescent detection (ECL) kit (Catalog # EK1002) with Tanon 5200 system. A specific band was detected for COMP at approximately 110 kDa. The expected band size for COMP is at 83 kDa |
| Gel % | 8–10% |
| Load | 30 ug |
| Transfer | nitrocellulose membrane, 150 mA, 50–90 min |
| Membrane | nitrocellulose |
| Blocking | 5% non-fat milk / TBS, 1.5 h RT |
| Primary antibody | 0.5 µg/mL |
| Primary incubation | overnight at 4 °C |
| Secondary antibody | goat anti-rabbit IgG-HRP, 1:5000 |
| Wash | TBS-0.1% Tween, 3 × 5 min |
| Detection | ECL |
| Exposure / imaging | Tanon 5200 |
| Observed band | 110 kDa |
Section 2
What Is the Expected COMP Western Blot Band Size?
COMP has an 82.9 kDa predicted backbone but runs at ~110 kDa on reducing blots due to N-linked glycosylation at two sites, with disulfide-linked pentamers appearing far higher if unreduced.
| single band near 110 kDa under reducing conditions | the glycosylated COMP monomer, elevated well above the 82.9 kDa predicted mass by N-linked glycosylation at Asn121 and Asn742 |
| band smearing or fuzziness around 100-120 kDa | heterogeneous carbohydrate loading across the two N-linked glycosylation sites broadening the monomer band |
| very high molecular weight band at or near the top of the gel or trapped in the stacking gel | the intact disulfide-linked pentamer running at roughly five times monomer mass because reduction was incomplete |
| little or no band in whole-cell lysate | COMP is secreted into the extracellular matrix, so a whole-cell lysate captures only the intracellular biosynthetic pool rather than the mature secreted protein |
| monomer band slightly smaller than the glycosylated full-length precursor | removal of the 20-residue signal peptide during secretion to yield the mature form |
💡Expected COMP appearanceUnder reducing conditions COMP typically runs as a single monomer band at approximately 110 kDa, well above its 82.9 kDa predicted mass due to N-linked glycosylation at two sites and signal peptide cleavage.
| predicted mass (UniProt, 82.9 kDa) | sets the unmodified polypeptide baseline before any processing or modification is accounted for |
| N-glycosylation at Asn121 and Asn742 | adds carbohydrate mass, shifting the observed reduced monomer up to roughly 110 kDa |
| signal peptide cleavage (residues 1-20) | removes the N-terminal signal sequence during secretion, slightly lowering mature protein mass relative to the unprocessed precursor |
| disulfide-linked pentamer assembly | under non-reducing or incompletely reduced conditions the intact oligomer migrates at roughly five times monomer mass near the top of the gel instead of the ~110 kDa monomer |
| isoforms 1 and 2 (alternative splicing) | can shift the monomer band slightly relative to the canonical form, described only qualitatively since no per-isoform mass is defined |
| Situation | Likely cause | Next action |
|---|---|---|
| No band in lysate | COMP is secreted into the extracellular space and matrix, so whole-cell lysate largely misses the mature extracellular pool | probe conditioned media or an extracellular matrix extraction instead of relying solely on whole-cell lysate |
| Band higher than expected | incomplete reduction leaves the disulfide-linked pentamer or partial oligomeric intermediates intact | increase reducing agent concentration and boil the sample longer to fully resolve the ~110 kDa monomer |
| Broad smear instead of sharp band | heterogeneous glycosylation across the two N-linked sites produces a range of glycoform masses | treat the sample with PNGase F to deglycosylate and sharpen the band, or extend separation on a lower-percentage gel |
| Multiple bands | co-migration of isoform 1 and isoform 2, or partially reduced oligomeric species alongside the monomer | confirm isoform identity with sequence-specific detection and verify complete denaturation and reduction of the sample |
| Fragments below expected size | proteolytic degradation of the secreted extracellular matrix protein during tissue or matrix extraction | include protease inhibitors and keep extracellular matrix samples cold and freshly processed |
Experiment evidence
Western blot images showing COMP band
A02443-1 · COMP
← swipe / scroll for more images →
Real WB data behind the band-size expectations in this section.
Sample controls for COMP Western blot
🧪For positive controls for COMP in Western blot, you can use cartilage tissue lysate or conditioned medium from a chondrocyte-derived cell line, since COMP (cartilage oligomeric matrix protein) is characteristically synthesized and secreted by chondrocytes.
Positive control: Cartilage tissue (chondrocytes)
Negative control: Non-cartilage cell line/tissue lacking COMP expression, or siRNA knockdown/KO
Loading controls: Run GAPDH and β-actin alongside a total-protein stain (e.g., stain-free gel, Ponceau S, or REVERT), though these cytoplasmic housekeeping proteins are a poor normalizer if probing secreted COMP in conditioned medium rather than whole-cell lysate.
⚠️Feasibility: As a secreted ECM protein, COMP gives little signal in standard whole-cell lysates, so conditioned medium or cartilage explant extracts are needed for a positive control, and since no HPA expression data are available for this gene, tissue/cell selection must rely on known cartilage-restricted biology rather than confirmed IHC or RNA-seq profiling.
Comprehensive Human Protein Atlas IHC scoring per tissue. Rows are taken directly from the HPA tissue chart — click any row's HPA link to view the source.
Positive expression · recommended positive controls
| Tissue | Cell type | Level | Evidence | Source |
|---|
Undetected expression · recommended negative controls
| Tissue | Cell type | Level | Evidence | Source |
|---|
Section 3
Advanced COMP Western Blot Tips
Deeper troubleshooting and optimisation questions for COMP, answered from its protein features.
Why does COMP run near 110 kDa instead of 82.9 kDa?
Predicted mass reflects the unmodified 82.9 kDa monomer after signal peptide cleavage. Native COMP carries 2 N-glycosylation sites and forms 23 disulfide bonds within each subunit, both of which reduce SDS-PAGE mobility and shift the apparent band upward. A ~110 kDa apparent band is consistent with a fully glycosylated, disulfide-bonded monomer rather than degradation or a distinct isoform.
Can COMP alternative splicing create multiple bands?
COMP has 2 annotated isoforms produced by alternative splicing. If your antibody targets a region present in both isoforms, expect closely spaced bands rather than a single sharp band; if it targets an isoform-specific exon, only one band should appear. Confirm the immunogen location against isoform sequences before flagging extra bands as nonspecific.
Does N-glycosylation change the observed band size?
COMP carries 2 predicted N-glycosylation sites but no other listed modified residues. Removing sugars with PNGase F should collapse a diffuse ~110 kDa signal into a sharper band closer to the 82.9 kDa core polypeptide, confirming glycosylation rather than aggregation or isoform differences as the source of the shift.
What blocking buffer works best for COMP blots?
COMP is a heparin-binding glycoprotein, so casein/milk-based blockers, which themselves contain glycoproteins and lectin-reactive sugars, can cause nonspecific background or false signal. A BSA-based blocking buffer is generally preferable for clean detection of glycoproteins like COMP; validate with a no-primary-antibody control on the same membrane.
What transfer method to use for COMP Western blot?
COMP assembles into a large disulfide-linked pentamer with 23 disulfide bonds per subunit, so ensure full reduction and denaturation with DTT/beta-mercaptoethanol and heat before loading. For the reduced ~110 kDa monomer, standard wet/tank transfer is recommended; extend transfer time if any higher-order oligomer persists after reduction.
How should COMP signal be normalized for quantitation?
COMP is secreted into the extracellular matrix rather than retained intracellularly, so standard loading controls like GAPDH or actin are not appropriate for conditioned media or ECM extracts. Use a total protein stain, such as Ponceau S or a stain-free gel, applied to the same membrane for normalization instead.
What explains unexpected bands above or below 110 kDa?
Bands above 110 kDa likely reflect incompletely reduced pentamer subunits, since 23 disulfide bonds require thorough reducing conditions to fully dissociate. Bands below 110 kDa may indicate degradation fragments, consistent with COMP's location in the extracellular matrix where extracellular proteolysis can occur; verify with a fresh lysate and protease inhibitors.
Boster reagents
Best COMP Western Blot Antibodies
BosterBio's COMP antibodies are among the best-performing WB antibodies on the market — well cited, thoroughly validated, and orthogonally cross-validated against negative tissues and complementary methods.
Real WB data
Anti-COMP Antibody Picoband®
Cat # A02443-1
The anti-COMP antibody below is Boster's top-performing option for cartilage oligomeric matrix protein detection, extensively cited and rigorously validated by western blot, with specificity confirmed against negative-control tissue and orthogonal detection methods for reliable, reproducible results.
Which to pick: Only A02443-1 is catalogued for COMP, backed by an actual western blot validation image, so it's the clear choice; no alternative clones are currently listed for comparison.
Source: BosterBio COMP gene-info card — filtered to Western-blot-capable antibodies; each card shows that product's actual WB validation figure.
References
- UniProt Consortium. UniProt entry P49747.
- Human Protein Atlas. COMP tissue expression.