152 entries

Streptavidin-saporin: Converting biotinylated materials into targeted toxins

Ancheta LR, Shramm PA, Bouajram R, Higgins D, Lappi DA (2023) Streptavidin-saporin: Converting biotinylated materials into targeted toxins. Toxins 15(3):181. doi: 10.3390/toxins15030181

Summary: This manuscript describes the myriad of ways Streptavidin-ZAP is used and how this technology supports the scientific process of ‘Molecular Surgery’ and progress in research and drug development. Insights from publications and research performed using Streptavidin-ZAP and its impact on academia and industry for research and drug development are presented.

Read the full article.

Related Products: Streptavidin-ZAP (Cat. #IT-27)

Equimolar mixing of Streptavidin-ZAP and Biotinylated Molecule

Question: I was wondering if you could elaborate on why the Streptavidin-ZAP product recommends to be used at an equimolar ratio with the targeting reagent, when it is capable of binding up to four biotins/molecule?

Answer: It’s a question we get asked sometimes and it’s a good question.

You are correct that streptavidin is capable of binding up to 4 biotin molecules.  However, when we created streptavidin-ZAP with the purpose of being a modular way of creating targeted toxins, we learned that the best general rule to follow was using a equimolar reaction.  In theory, it is a 1:1 ratio of targeting molecule to streptavidin-ZAP, where we are most likely seeing an average of 1:1, but there is also the possibility of mixed ratios.

The amount of publications using the equimolar approach gave the desired results whether they were using a small biotinylated peptide or whole IgG.  You’ll notice that depending on the MW of your biotinylated targeting agent, the amount of streptavidin-ZAP needed for the experiment can vary drastically and through in-house characterization, the equimolar approach still worked best. 

Another reason we recommend a 1:1 ratio is based on our experience with our other secondary conjugates. It may be intuitive to think that using a higher dose of targeting agent would induce more cell death, but we found the opposite effect, where the excess, un-reacted targeting agent competed with the conjugated material for surface binding sites, which in turn decreased the amount of saporin being delivered. We have a publication (PMCID: PMC8952126 ) that also describes this observation.  

Once you’ve created a baseline using the equimolar protocol and are more accustomed to how streptavidin-ZAP works in your application, please contact us if you feel more optimization is needed.  It will be easier to help trouble-shoot when we are all working off the same protocol.

Related Products: Streptavidin-ZAP


  1. Ancheta LR et al. Saporin as a commercial reagent: its uses and unexpected impacts in the biological sciences-tools from the plant kingdom. Toxins (Basel) 14(3):184, 2022.

Which type of RIP is saporin?

Q: I read on your website that, “There are two types of RIPs: type I, which are much less cytotoxic due to the lack of the B chain and type II, which are distinguished from type I RIPs by the presence of the B chain and their ability to enter cells on their own.”

In the IT-27 Streptavidin-ZAP product, which type of saporin is there? Is it both type I and type II because the saporin is purified from the plant, or is it one specific type only in the product.

A: All saporin molecules are Type I ribosome-inactivating proteins. We only use saporin. An example of a Type II RIP is ricin, which can enter a cell on its own and has been used throughout history as a method of assassination.

Streptavidin-ZAP is streptavidin attached to saporin. On its own it has no way to get inside a cell. By mixing Streptavidin-ZAP with a biotinylated molecule that is recognized on the cell surface, the resulting conjugate is able to bind and internalize saporin into a cell. Once inside saporin inactivates the ribosomes which causes cell death.

CD3e-immunotoxin spares CD62Llo Tregs and reshapes organ-specific T-cell composition by preferentially depleting CD3ehi T cells

Kim S, Shukla RK, Yu H, Baek A, Cressman SG, Golconda S, Lee GE, Choi H, Reneau JC, Wang Z, Huang CA, Liyanage NPM, Kim S (2022) CD3e-immunotoxin spares CD62Llo Tregs and reshapes organ-specific T-cell composition by preferentially depleting CD3ehi T cells. Front Immunol 13:1011190. doi: 10.3389/fimmu.2022.1011190

Objective: To use a new murine testing model to demonstrate a substantial enrichment of tissue-resident Foxp3+ Tregs following CD3e-IT treatment.

Summary: The multi-organ pharmacodynamics of CD3e-IT and potential treatment resistance mechanisms identified in this study may generate new opportunities to further improve this promising treatment.

Usage: Male C57BL/6J mice were injected into retro-orbital sinus with 15 μg S-CD3e-IT (Biotinylated Anti-CD3 mixed with Streptavidin-ZAP in sterile 200 μl PBS twice a day for four consecutive days.

Related Products: Streptavidin-ZAP (Cat. #IT-27)

Fab-ZAP Final Concentration

Q: When using any of your Fab-Zap product line, the recommended final concentration is 4.5 nM. Is this based on experiments you have done? I question if at 4.5 nM my primary antibody will be saturated with Fab-ZAP secondary conjugate?

A: Yes, the 4.5 nM concentration is what we use to quality-control test our Fab-ZAP conjugates and why we recommend it in the literature.  We also recommend only titrating your primary antibody.  The 4.5 nM of Fab-ZAP should be enough to saturate your primary antibody.  If you have a test of ~10 nM of primary antibody and you experience less cell death than ~1 nM, this will indicate “antibody competition” (i.e., your primary antibody is not saturated).  The data sheet shows a cytotox with a nice example of this. (Fab-ZAP data sheet)

See: Fab-ZAP human (Cat. #IT-51)

In vivo visualization and molecular targeting of the cardiac conduction system

Goodyer WR, Beyersdorf BM, Duan L, van den Berg NS, Mantri S, Galdos FX, Puluca N, Buikema JW, Lee S, Salmi D, Robinson ER, Rogalla S, Cogan DP, Khosla C, Rosenthal EL, Wu SM (2022) In vivo visualization and molecular targeting of the cardiac conduction system. J Clin Invest e156955. doi: 10.1172/jci156955

Objective: To engineer targeted antibody conjugates directed against the cardiac conduction system (CCS) to allow visualization of the CCS in vivo.

Summary: Accidental injury to the CCS, a specialized set of cells embedded within the heart and indistinguishable from the surrounding heart muscle tissue, is a major complication in cardiac surgeries. They generated a fully human monoclonal Fab (hCNTN2) that targets the CCS with high specificity.

Usage: Streptavidin-ZAP was reacted with biotinylated hCNTN2 Fab to create hCNTN2-SAP. 100 ug of either hCNTN2-SAP and control-SAP were injected into wild-type mice with a single tail-vein injection and hearts were harvested after 2 days.

Related Products: Streptavidin-ZAP (Cat. #IT-27)

Antibody-based preparative regimens for cell, tissue and organ transplantation

Van Hentenryck M, Li Z, Murphy PM, Czechowicz A (2022) Antibody-based preparative regimens for cell, tissue and organ transplantation. (eds. 162). OBM Transplantation 6(3):162. doi: 10.21926/obm.transplant.2203162

Objective: Provide a review of progress in the use of antibodies to support cell and tissue transplantation with a particular focus on induction of donor-specific tolerance for solid organ transplantation.

Summary: Antibody-based conditioning to prepare the recipient is a promising approach towards achieving transplant tolerance in both hematopoietic and solid organ transplant settings.

Usage: To enhance HSC depletion while avoiding bystander toxicity (neutropenia, lymphopenia, and thrombocytopenia) caused by CD45-radioimmunotherapy, Palchaudhuri et al. developed a saporin-based CD45 (CD45-SAP) immunotoxin using a biotinylated antibody and Streptavidin-ZAP.

Related Products: Streptavidin-ZAP (Cat. #IT-27)

See Also:

Mab-ZAP binds to Fc portion of mouse IgG

Q: Does Mab-ZAP (Cat. #IT-04) bind to the FC portion of mouse IgG?

A: The antibody used to create our Mab-ZAP (IT-04), will react with whole molecule mouse IgG, which includes the Fc portion and the two antigen binding Fab portions.

Related Products: ZAP Conjugates

FabFc-ZAP cross-reaction with another species

Q: Can your FabFc-ZAP human (Cat# IT-65) bind to the Fc portion of another species, such as mouse IgG? It looks like it binds to mouse IgG in our assay.

A: The antibody used to create our FabFc-ZAP Human (IT-65), can react with the Fc (gamma) portion of human IgG heavy chain and should not react with the Fab portion of human IgG. However, there could be minimal cross-reaction with mouse, horse, or bovine serum proteins, and it is possible to see cross-reaction with immunoglobulins from other species. 

Related Products: ZAP Conjugates

Comparison of CD3e antibody and CD3e-sZAP immunotoxin treatment in mice identifies szap as the main driver of vascular leakage

Kim S, Shukla RK, Kim E, Cressman SG, Yu H, Baek A, Choi H, Kim A, Sharma A, Wang Z, Huang CA, Reneau JC, Boyaka PN, Liyanage NPM, Kim S (2022) Comparison of CD3e antibody and CD3e-sZAP immunotoxin treatment in mice identifies szap as the main driver of vascular leakage. Biomedicines 10(6):1221. doi: 10.3390/biomedicines10061221

Objective: Investigate and identify the toxicity profiles of a CD3e-mAb and an immunotoxin of this CD3e antibody conjugated to saporin via a biotin-streptavidin bond, S-CD3e-IT.

Summary: The two agents had opposite effects on T cells, with the antibody alone able to modulate CD3e on the cell surface while the S-CD3e-IT caused depletion of the cell. The immunotoxin increased the infiltration of polymorphonuclear leukocytes (PMNs) into the tissue parenchyma of the spleen and lungs, a sign of vascular permeability while the antibody alone showed no signs of vascular leakage.

Usage: S-CD3e-IT was prepared by reacting biotinylated CD3e antibody with Streptavidin-ZAP in a 1:1 molar ratio. C57BL/6J mice received 25 μg of S-CD3e-IT in sterile 200 μL PBS, twice a day via retro-orbital injection for four days.

Related Products: Streptavidin-ZAP (Cat. #IT-27)

Dosage of Fab-ZAP for antibody concentration

Q: Is the dosage of Fab-ZAP always enough for any level of antibody concentration?

A: The 4.5 nM dosage of Fab-ZAP is the recommended concentration.  We do not typically see unspecific killing at 4.5 nM on most cell lines.  If the concentration of Fab-ZAP is increased, it may undergo bulk-phase endocytosis and kill cells indiscriminately.  A lower concentration of Fab-ZAP may lead to antibody competition, resulting in a lack of killing of cells at the highest concentration of antibody.

Related Products: ZAP Conjugates

Recommended ratio between Fab-ZAP dosage and antibody concentration

Q: Is there a recommended ratio between Fab-ZAP dosage and antibody concentration?

A: A recommended good starting point is 4.5 nM of Fab-ZAP, with a titration of the antibody starting at a concentration of 10 nM.

Related Products: ZAP Conjugates

Adjust number of replications

Q: Each concentration is suggested to perform 6 replications, can it be adjusted more or less in practice?

A: Yes, the assay design is meant to be a thorough approach but can be adjusted by the user. We recommend 6 replications based on our 96-well plate template design. The concentration of Fab-ZAP is 4.5 nM in the suggested protocols.

Related Products: ZAP Conjugates

Detecting the targeted antibody in supernatant

Q: Can Fab-ZAP detect the targeted antibody still in supernatant?

A: As long as there is nothing in the supernatant inhibiting the reactivity of Fab-ZAP, it should work.  We do not typically recommend this, but in theory it should be possible.  I would be cautious of this approach based off of the presumed lack of established concentration of antibody.

Related Products: ZAP Conjugates

DMSO% for peptide and Streptavidin-ZAP

Q: Instead of performing the reaction between our biotinylated peptide and Streptavidin-ZAP at the initially provided concentration of Strep-ZAP (20 µM), is it OK if the reaction is done at a 10-fold more dilute concentration? This request is to ensure we don’t have any solubility problems with our very tricky lipophilic peptide. Our protocol would be to first dilute Streptavidin-ZAP to 2 µM with PBS and then add the peptide in DMSO (10% final), and store the aliquoted resulting 1.82 µM solution?

A: In regards to your question, while keeping in mind your solubility concerns, we suggest that you:

  1. Proceed with diluting the Streptavidin-ZAP to 2 uM with PBS as you suggest, BUT, only react the amount of Streptavidin-ZAP necessary for the next step.
  2. Store the undiluted and unreacted Streptavidin-ZAP at -80°C until you’re ready for more conjugate.

We understand the solubility of the peptide is a concern, and rightfully so.  However, we also do not want to compromise the Streptavidin-ZAP during storage, considering its value.

Related Products: ZAP Conjugates

ZAP Internalization Kit Concentrations

Q: We have your ZAP internalization kit and I have a question regarding the concentrations used in the cytotoxicity assay. The Hum-ZAP used in the assay (mentioned in the PDF protocol) is 4.5 nM and the target agent was 10 nM to 1 fM. Is there a stoichiometric relation between Hum-ZAP and the target agent concentrations?

A: To answer your question simply, yes, there is a stoichiometric relation between a secondary conjugate and the targeting agent.

Q: If I use higher concentrations of the target antigen, then should I also increase the concentration of Hum-ZAP?

A: It may be intuitive to think that using a higher dose of primary antibody induces a higher amount of cell death, but as seen in the attached figure, at the highest concentration of 192-IgG (10 nM = Log -8) there is a lessened amount of killing, at a 25-fold lower concentration, as compared to the antibody. The explanation for this is that, at the higher concentrations of primary antibody, there is more unconjugated 192-IgG and fewer 192-IgG+Fab-ZAP complexes. The free 192-IgG then out-competes the conjugates for cell surface binding sites which, in turn, decreases the amount of Saporin being internalized, hence less cell death.

Related Products: ZAP Conjugates

Saporin as a commercial reagent: its uses and unexpected impacts in the biological sciences-tools from the plant kingdom

Ancheta LR, Shramm PA, Bouajram R, Higgins D, Lappi DA (2022) Saporin as a commercial reagent: its uses and unexpected impacts in the biological sciences-tools from the plant kingdom. Toxins (Basel) 14(3):184. doi: 10.3390/toxins14030184

Read complete article.

Host receptor-targeted therapeutic approach to counter pathogenic New World mammarenavirus infections

Hickerson BT, Daniels-Wells TR, Payes C, Clark LE, Candelaria PV, Bailey KW, Sefing EJ, Zink S, Ziegenbein J, Abraham J, Helguera G, Penichet ML, Gowen BB (2022) Host receptor-targeted therapeutic approach to counter pathogenic New World mammarenavirus infections. Nat Commun 13(1):558. doi: 10.1038/s41467-021-27949-3

Objective: Demonstrate that a fusion protein of the antibody (ch128.1/IgG1) directed against the apical domain of human transferrin receptor 1 (hTfR1) and the Machupo virus (MACV) can inhibit infection of attenuated and pathogenic New World mammarenaviruses (NWMs).

Summary: NWMs cause life-threatening hemorrhagic fever (HF) and these viruses enter into cells via hTfR1. Use of ch128.1/IgG1 with other promising direct-acting small molecule antivirals or antibodies targeting the viral envelope glycoprotein would provide a complementary therapeutic strategy that would increase efficacy and reduce the emergence of drug resistance.

Usage: References MonoBiotin-ZAP reacted with avidinylated anti-hTfR (ch128.1Av) in a 1:1 molar ratio on ice for 30 minutes.

Related Products: MonoBiotin-ZAP (Cat. #BT-ZAP)

See Also:

Antibody-drug conjugates plus Janus kinase inhibitors enable MHC-mismatched allogeneic hematopoietic stem cell transplantation

Persaud SP, Ritchey JK, Kim S, Lim S, Ruminski PG, Cooper ML, Rettig MP, Choi J, DiPersio JF (2021) Antibody-drug conjugates plus Janus kinase inhibitors enable MHC-mismatched allogeneic hematopoietic stem cell transplantation. J Clin Invest 131(24):e145501. doi: 10.1172/JCI145501

Objective: To demonstrate that biotinylated anti-CD45-SAP or anti-cKit-SAP mixed with Streptavidin-Saporin along with Janus kinase 1/2, enables alloengraftment on murine allo-hematopoietic stem cell transplantation (HSCT) models.

Summary: HSCT has therapeutic potential. However, the transplantation requires first depletion and secondly, for allogeneic-HCST, host and immune responses need to be controlled to prevent graft rejection. The allo-HSCT conditioning strategy exemplifies the promise of immunotherapy to improve the safety of HSCT for treating hematologic diseases.

Usage: Antibodies were incubated with Streptavidin-ZAP (1:1 molar ratio) for 15 minutes at 20°C and . The doses of CD45.2 and cKit conjugates were injected retroorbitally (41.8 μg and 33.2 μg, respectively).

Related Products: Streptavidin-ZAP (Cat. #IT-27)

Enhancing the therapeutic potential of extracellular vesicles using peptide technology

Martin Perez C, Conceição M, Raz R, Wood MJA, Roberts TC (2022) Enhancing the therapeutic potential of extracellular vesicles using peptide technology. (eds. Langel Ü). In: Cell Penetrating Peptides. Methods in Molecular Biology 2383:119-141. Humana, New York, NY. doi: 10.1007/978-1-0716-1752-6_8

Objective: To modify EVs with peptides which confer specific advantageous properties, thus enhancing their therapeutic potential.

Summary: The authors provide an overview of the applications of peptide technology with respect to EV therapeutics. We focus on the utility of EV-modifying peptides for the purposes of promoting cargo loading, tissue-targeting and endosomal escape, leading to enhanced delivery of the EV cargo to desired cells/tissues and subcellular target locations. Both endogenous and exogenous methods for modifying EVs with peptides are considered.

Usage: Streptavidin-ZAP is combined with biotinylated peptides to make a targeted saporin conjugate.

Related Products: Streptavidin-ZAP (Cat. #IT-27)

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