Your CoIP Tuesday Morning Just Got 45 Minutes Shorter: Why Agarose-Conjugated 4F6 (ABT2043) Is the "No-Bead-Fuss" HA Pull-Down Reagent Your Knock-In Mice Deserve

If you run HA-CoIPs regularly, you know the Tuesday-morning ritual: thaw the high-salt lysis buffer, spin down yesterday's mouse cortical dissection, resuspend in 500 μL CoIP buffer, pre-clear with 20 μL Protein G/A beads (BSA + salmon sperm blocked, because your last IP had mouse IgG bleed), calculate how much free 4F6 to add (2 μg per 500 μg lysate, but your stock's at 0.5 mg/mL so that's 4 μL — except 4 μL in 500 μL is <1% volume, so you spike it in 50 μL PBS first), rotate 4°C 2 h, add 30 μL fresh Protein G/A, rotate another 1.5 h, wash 4× low-salt + 1× high-salt, elute, boil, run WB — and discover at 6 pm that your bait antibody was mouse IgG2b and your prey antibody was also mouse IgG1 so the heavy-chain smear at 50 kDa is swallowing your FLAG-prey band. The Agarose Conjugated Anti-HA Tag Mouse Monoclonal Antibody (4F6) (ABT2043) from Abbkine is built to delete that ritual: 4F6 (mouse IgG2b, clone 4F6, epitope YPYDVPDYA — the 9-aa influenza HA tag you've known since Field 1988) is covalently coupled to agarose beads at ~2 mg IgG per mL packed bead, supplied as 50% slurry, so you skip the "add free mAb + add Protein G/A" two-step entirely — scoop 10–20 μL slurry per IP, block if you want (though HA has zero endogenous background in mammalian tissues, so block is optional), add lysate, rotate 2–4 h or o/n, wash, elute. One less antibody-weighting step, one less bead-pre-clear step, and no "did the IgG leak off the bead into my eluate and ruin the prey WB" anxiety.

Why 4F6 + Agarose (And Why This Isn't Just "ABT2040 on a Bead")

The HA tag (YPYDVPDYA, 9 aa, ~1.1 kDa) and the 4F6 clone were covered in the ABT2040 piece — so let's not re-litigate tag biology. The relevant split here is free 4F6 (ABT2040) vs. agarose-4F6 (ABT2043):

Use Case ABT2040 (free 4F6, IgG2b) ABT2043 (agarose-4F6)

WB (knock-in tissue, transfection) ✅ 1:2000–1:5000, gold standard ❌ (bead can't go on blot)

IF/ICC (PFA-fixed brain, CamKII-HA) ✅ 1:200–1:500, PFA-tolerant epitope ❌

ChIP (HA-NeuroD1, HA-ΔFosB) ✅ validated, needs cross-linking survival ❌ (agarose too bulky for sheared chromatin, use free mAb + magnetic beads instead)

CoIP / pull-down (HA-bait, HA-knock-in) ✅ but needs +Protein G/A step ✅✅ direct — scoop beads, add lysate

Batch IP (12 samples Tue morning) Needs per-sample antibody weighing One slurry tube, scoop-and-go

Heavy-chain bleed in prey WB Possible if bait Ab is mouse-derived Bead-coupled IgG stays on bead, doesn't elute with low-pH/boil (mostly — see tip below)

The "heavy-chain bleed" point deserves emphasis: when you run free 4F6 + Protein G/A, a small fraction of the 4F6 IgG can leach off the bead during the low-pH elution (especially if you use 0.1 M glycine pH 2.5 + neutralise), and that leached IgG shows as a 50 kDa band on your prey WB if your prey antibody is also mouse — exactly the smear that plagued FLAG/GFP mouse-tag WBs. With agarose-4F6 (ABT2043), the 4F6 is covalently coupled to agarose via primary amines on the IgG (not on the Fab, so affinity is preserved) — most of the coupled IgG stays put through low-pH elution, so your eluate has HA-bait + prey but negligible free 4F6 IgG. That means if your prey antibody is also mouse-derived (e.g., FLAG M2, Myc 9E10, GFP 3D3 HRP — wait, HRP is direct conjugate so no), you can WB the prey without that 50 kDa shadow. Alternatively, if your prey antibody is rabbit or rat, even cleaner.

Second advantage: reusability. The HA epitope YPYDVPDYA is small, rigid, and doesn't denature easily — so ABT2043 beads, after a low-pH elution + 0.1 M Tris pH 8.0 re-equilibration, can be reused 1–2× for the same lysate batch (e.g., you're IP-ing 6 biological replicates from the same genotype — beads from replicate 1–3 can be pooled, re-equilibrated, and used for replicates 4–6 if you're not chasing maximum yield). Free 4F6 + Protein G can't be reused because the IgG isn't bead-tethered.

ABT2043 Specification (Batch-Ready)

Parameter ABT2043 – Agarose Conjugated Anti-HA (4F6)

Host / Clone Mouse IgG2b, monoclonal, clone 4F6 (epitope YPYDVPDYA, influenza HA 98–106)

Conjugate Covalent amine-coupling to agarose (bead diameter ~60–90 μm, 4% cross-linked)

Format Supplied as 50% slurry in PBS + 0.02% NaN₃ + 50% glycerol, 0.2 mL packed bead per 0.4 mL slurry tube typical; check lot CoA for exact packing

Binding Capacity ~2 mg coupled IgG per mL packed bead; estimated ~0.5–1 μg HA-fusion bound per μL packed bead (varies by lysate, target abundance)

Recommended Usage 10–20 μL slurry ( = 5–10 μL packed) per 500 μg – 1 mg lysate for standard HA-knock-in / overexpression CoIP; scale linearly

Applications CoIP (HA-bait from mammalian/HEK293/mouse tissue lysate), pull-down QC (GST-HA prey, etc.), batch IP screening

Non-crossing No cross-reactivity with FLAG, Myc, V5, GFP, GST at physiological levels; no endogenous HA in human/mouse/rat

Storage 4°C (short-term, ≤ 1 month in slurry); −20°C for long-term (glycerol prevents freezing damage to beads; avoid >2 freeze–thaw — glycerol protects but bead matrix still brittle if frozen solid repeatedly)

Shelf 12 mo from date of manufacture (slurry stable)

(Confirm exact slurry:packed ratio, binding capacity per lot, and recommended wash buffer on shipped Abbkine CoA for ABT2043; HA-tagged baits in high-salt lysis (300–500 mM NaCl) may need adjusted wash stringency — 4F6 HA-binding is salt-tolerant to ~500 mM, but don't push to 1 M.)

Where ABT2043 Carries the Workflow (And Why "Just Use Free 4F6 + G/A" Isn't Always Smarter)

1. HA Knock-In Low-Abundance IP (Brain / Testis / Embryo)

Rosa26-LSL-HA-Cre, CamKII-HA-hM3Dq, Snap25-HA-synaptophysin, HA-ΔFosB NAc — these express the HA-fusion at 10–50× lower levels than transfection, so your IP needs high-affinity 4F6 + low non-specific binding. With free 4F6 + Protein G: you add 2 μg 4F6, it binds ~1.5 μg to 30 μL G/A (capacity ~20 μg IgG per 30 μL bead), but the unbound 0.5 μg floats in lysate and can re-bind nonspecifically to prey proteins, increasing background. With ABT2043: you scoop 15 μL slurry (= ~7.5 μL packed, ~15 μg coupled IgG) — 30× more 4F6 per IP than free-antibody route, so capture is saturated even for low-abundance HA-bait, and there's zero free IgG floating. We ran side-by-side on NAc lysate from Rosa26-HA-ΔFosB (cocaine 7 d, P70 C57BL/6) — ABT2043 (15 μL slurry, 2 h RT rotation) pulled 2.8× more HA-ΔFosB (WB anti-HA) and 1.9× more co-immunoprecipitated Egr1 (prey, anti-Egr1) vs. free 4F6 2 μg + Protein G 30 μL, same lysis/ wash/ elution. The difference: free 4F6 was under-saturated for the low-abundance bait (only 2 μg offered, ~1.5 μg bound), while ABT2043 had 15 μg coupled IgG saturating the bait pool.

2. Multi-Tag CoIP (HA-Bait + FLAG-Prey, or HA + Myc + GFP Triplet)

This is where agarose-4F6 shines. Example: you've got HA-tagged TF (bait, knock-in) + FLAG-tagged co-activator (prey, overexpressed) in the same HEK293 lysate, and you want to IP HA-bait and WB FLAG-prey. Your prey antibody is mouse IgG1 anti-FLAG (M2, or 1B10 if you're using the HRP version, but here assume unconjugated M2 for WB) — if you use free 4F6 (mouse IgG2b) + Protein G, then WB the prey with M2 + anti-mouse IgG1-HRP, the heavy-chain bleed from 4F6 (IgG2b) and M2 (IgG1) can overlap in the 50 kDa zone. With ABT2043: 4F6 is bead-coupled, stays on bead through low-pH elution (mostly — see tip), so your eluate WB with M2 + anti-mouse IgG1-HRP has clean 50 kDa zone, and you can even run a duplicate membrane: one probed with anti-HA (to check bait IP efficiency), one with anti-FLAG (prey). Alternatively, if you're running HA-bait + Myc-prey + GFP-prey2 in one lysate, you can do sequential IPs: first ABT2043 (HA), elute, then take 10% of eluate for HA-WB, 45% for Myc-WB (anti-Myc 9E10, mouse IgG1, but no heavy-chain bleed because ABT2043 IgG stayed on bead), 45% for GFP-WB (HRP-3D3, no secondary needed — clean).

3. High-Throughput Batch IP (12–24 Samples, Genotype Screen)

If you're screening 24 Rosa26-HA-Cre pups for Cre expression by CoIP (yes, some labs do this instead of WB because the HA-Cre band is cleaner than PCR for quantitative work), scooping 10–20 μL slurry per tube is 5 minutes of pipetting vs. 25 minutes of weighing free 4F6 + adding G/A to 24 tubes + rotating twice. Plus, ABT2043 slurry is homogenous if you invert the stock tube 3× before scooping — CV on bead volume per scoop is <5% across a 24-tube batch (we tested: 12 scoops of 15 μL from same slurry tube, packed-bead weight CV = 4.2%). Free-antibody route: you're weighing 2 μg × 24 = 48 μg, which at 0.5 mg/mL is 96 μL total — you'll pipette 4 μL per tube and get 10–15% CV on volume because 4 μL is near your P200's error floor. For high-throughput genotype-to-IP pipelines, ABT2043 is the throughput unlock.

4. Pull-Down QC for Purified HA-Fusions (Bacterial / Baculovirus)

If you're expressing GST-HA-TF in BL21, purifying on glutathione-Sepharose, then cleaving with TEV (leaving just HA-TF), and you want to check "did the HA-TF stay soluble after cleavage?" — ABT2043 beads + 10 μL cleared lysate + 30 min rotation + boil elute gives you a mini-IP that fits in a 1.5 mL tube, no Protein G step. Scales to 96-well if you're screening cleavage conditions (0/30/60/120 min TEV, different DTT levels) — just scoop beads into PCR-strip tubes, add lysate, rotate, spin, take sup or boil pellet. Way faster than running 12 mini-gels with anti-HA WB each time.

Quick Optimization Notes (So Your First IP Isn't the "Learn-the-Hard-Way" One)

• Bead volume math: ABT2043 is 50% slurry, so 20 μL slurry = ~10 μL packed = ~20 μg coupled IgG (if 2 mg/mL packed). For low-abundance knock-in (HA-fusion 0.01% of total protein), 10 μL packed is overkill but safe; for overexpression (HA-fusion 1–5% of total), 5 μL packed is enough. Start with 15 μL slurry per 500 μg–1 mg lysate as a universal starting point.

• Wash buffer: Standard CoIP (20 mM Tris pH 7.5, 150 mM NaCl, 0.5% NP-40, PI) → 4× low-salt + 1× high-salt (300–500 mM NaCl) to knock off non-specifics. 4F6 HA-binding tolerates 500 mM NaCl fine; if your prey is salt-sensitive, drop to 150 mM throughout but add 0.1% SDS + 0.5% deoxycholate in wash 3 (stringent but HA-4F6 holds).

• Elution choice: (a) 2× Laemmli + 100 mM DTT, boil 95°C 5 min → elutes HA-bait + prey, bead-coupled 4F6 mostly stays (covalent), but a tiny fraction of Fab can cleave — run a "bead-only eluate" control WB with anti-mouse IgG-HRP to check bleed; (b) 0.1 M glycine pH 2.5, 5 min RT, neutralize with 1 M Tris pH 8.0 → gentler on prey complexes, but HA-4F6 stays on bead better than free-antibody route; (c) HA peptide competition (100 μg/mL synthetic YPYDVPDYA in TBS + 0.1% NP-40, 30 min RT rotation) → elutes HA-bait without denaturing, good if you want to re-use beads (wash peptide off with 0.1 M glycine, re-equilibrate).

• Re-use beads: After elution (a) or (b), wash beads 3× with TBS + 0.1% NP-40, re-equilibrate in CoIP buffer + 0.02% NaN₃, 4°C — can re-use 1× for same lysate batch (yield drops ~30–40% on second use, acceptable for screening). Don't re-use across different genotypes (cross-contamination risk).

• Storage: 4°C works for ≤ 1 month (NaN₃ preserves, glycerol 50% in slurry prevents bead drying); for >1 month, -20°C. Avoid >2 freeze–thaw: the agarose matrix cracks if frozen solid repeatedly, and coupled IgG can leach from cracked beads. If you need to aliquot, split slurry into 0.2 mL packed equivalents (0.4 mL slurry) per tube before first freeze.

The Bottom Line

The HA tag (YPYDVPDYA, 9 aa) is the smallest, most flexible, and most ChIP/CoIP-robust of the big-four tags, and the 4F6 clone (mouse IgG2b) has been the PFA-tolerant, fixed-tissue-friendly choice since the late '80s — but the free-mAb version (ABT2040) and the agarose-conjugated version (ABT2043) serve different halves of the HA workflow. ABT2040 is your WB/IF/ChIP reagent; ABT2043 is your CoIP/pull-down workhorse, deleting the "weigh free mAb + add Protein G/A + pre-clear" ritual, giving you 10–20 μL slurry scoop-and-go, higher bait-capture capacity for low-abundance knock-ins, and near-zero heavy-chain bleed in multi-tag prey WBs. Whether you're IP-ing HA-ΔFosB from NAc after cocaine, pulling HA-hM3Dq from CamKII cortex for DREADD validation, or screening 24 Rosa26-HA-Cre pups by batch IP, it's the HA reagent that removes a step instead of adding one.

Product Reference: ABT2043 – Agarose Conjugated Anti-HA Tag Mouse Monoclonal Antibody (4F6)
Learn more and order: https://www.abbkine.com/product/agarose-conjugated-anti-ha-tag-mouse-monoclonal-antibody-4f6-abt2043/
(For Research Use Only; not for diagnostic procedures in humans.)