Siglec-3/CD33 Antibody (L008.2.25LL) [Unconjugated]

HEK293 human embryonic kidney cell line transfected with either (A) human Siglec-3/CD33 or (B) irrelevant protein and eGFP was stained with Llama Anti-Human Siglec-3/CD33 Llamabody Native IgG Monoclonal Antibody (Catalog # LMAB10902) followed by Goat Anti-Llama Secondary Antibody (AF011), and then Allophycocyanin-conjugated Anti-Goat IgG Tertiary Antibody (F0108). Quadrant markers were set based on secondary plus tertiary antibody staining in the absence of primary antibody. View our protocol for Staining Membrane-associated Proteins.

• Reactivity: Hu
• Applications: Flow
• Clone: L008.2.25LL
• Clonality: Monoclonal
• Host: Llama
• Conjugate: Unconjugated

Siglec-3/CD33 Antibody (L008.2.25LL) [Unconjugated] Summary

• Additional Information: Recombinant Monoclonal Antibody. Bivalent Llama VHH domain, Llama IgG2 Fusion Antibody.
• Immunogen: Mouse myeloma cell line NS0-derived human Siglec-3/CD33 protein as immunogen for bivalent Llama V_HH-Llama IgG2 Fusion Antibody
  Asp18-His259
  Accession # AAA51948
• Specificity: Clone L008.2.25LL is a bivalent Llama V_HH-Llama IgG2 Fusion Antibody that detects human Siglec-3/CD33 in direct ELISAs. Antibody construct is depicted below.

  Human Siglec-3/CD33 Specific Llama VHH domain	Llama Hinge	Llama IgG2
  N-terminus		C-terminus

• Source: N/A
• Clonality: Monoclonal
• Host: Llama
• Purity Statement: Protein A or G purified from cell culture supernatant

Applications/Dilutions

• Dilutions:
  • Flow Cytometry 0.25 ug/10^6 cells

Packaging, Storage & Formulations

• Storage: Use a manual defrost freezer and avoid repeated freeze-thaw cycles.
  • 12 months from date of receipt, -20 to -70 °C as supplied.
  • 1 month, 2 to 8 °C under sterile conditions after reconstitution.
  • 6 months, -20 to -70 °C under sterile conditions after reconstitution.
• Buffer: Lyophilized from a 0.2 μm filtered solution in PBS with Trehalose. *Small pack size (SP) is supplied either lyophilized or as a 0.2 µm filtered solution in PBS.
• Reconstitution Instructions: Reconstitute at 0.5 mg/mL in sterile PBS.

Notes

This product is produced by and ships from R&D Systems, Inc., a Bio-Techne brand.

Alternate Names for Siglec-3/CD33 Antibody (L008.2.25LL) [Unconjugated]

• CD33 antigen (gp67)
• CD33 antigen
• CD33 molecule
• CD33
• FLJ00391
• gp67
• myeloid cell surface antigen CD33
• p67
• sialic acid binding Ig-like lectin 3
• Sialic acid-binding Ig-like lectin 3
• Siglec3
• Siglec-3
• SIGLEC3gp67

Background

SARS-CoV-2, which causes the global pandemic coronavirus disease 2019 (Covid-19), belongs to a family of viruses known as coronaviruses that are commonly comprised of four structural proteins: Spike protein(S), Envelope protein (E), Membrane protein (M), and Nucleocapsid protein (N) (1). SARS-CoV-2 Spike Protein (S Protein) is a glycoprotein that mediates membrane fusion and viral entry. The S protein is homotrimeric, with each ~180-kDa monomer consisting of two subunits, S1 and S2 (2). In SARS-CoV-2, as with most coronaviruses, proteolytic cleavage of the S protein into two distinct peptides, S1 and S2 subunits, is required for activation. The S1 subunit is focused on attachment of the protein to the host receptor while the S2 subunit is involved with cell fusion (3-5). Based on structural biology studies, the receptor binding domain (RBD), located in the C-terminal region of S1, can be oriented either in the up/standing or down/lying state (6). The standing state is associated with higher pathogenicity and both SARS-CoV-1 and MERS can access this state due to the flexibility in their respective RBDs. A similar two-state structure and flexibility is found in the SARS-CoV-2 RBD (7). Based on amino acid (aa) sequence homology, the SARS-CoV-2 S1 subunit RBD has 73% identity with the RBD of the SARS-CoV-1 S1 RBD, but only 22% homology with the MERS S1 RBD. The low aa sequence homology is consistent with the finding that SARS and MERS bind different cellular receptors (8). The S Protein of the SARS-CoV-2 virus, like the SARS-CoV-1 counterpart, binds Angiotensin-Converting Enzyme 2 (ACE2), but with much higher affinity and faster binding kinetics (9). Before binding to the ACE2 receptor, structural analysis of the S1 trimer shows that only one of the three RBD domains in the trimeric structure is in the "up" conformation. This is an unstable and transient state that passes between trimeric subunits but is nevertheless an exposed state to be targeted for neutralizing antibody therapy (10). Polyclonal antibodies to the RBD of the SARS-CoV-2 protein have been shown to inhibit interaction with the ACE2 receptor, confirming RBD as an attractive target for vaccinations or antiviral therapy (11). There is also promising work showing that the RBD may be used to detect presence of neutralizing antibodies present in a patient's bloodstream, consistent with developed immunity after exposure to the SARS-CoV-2 virus (12). Lastly, it has been demonstrated the S Protein can invade host cells through the CD147/EMMPRIN receptor and mediate membrane fusion (13, 14).

1. Wu, F. et al. (2020) Nature 579:265.
2. Tortorici, M.A. and D. Veesler (2019). Adv. Virus Res. 105:93.
3. Bosch, B.J. et al. (2003). J. Virol. 77:8801.
4. Belouzard, S. et al. (2009) Proc. Natl. Acad. Sci. 106:5871.
5. Millet, J.K. and G. R. Whittaker (2015) Virus Res. 202:120.
6. Yuan, Y. et al. (2017) Nat. Commun. 8:15092.
7. Walls, A.C. et al. (2010) Cell 180:281.
8. Jiang, S. et al. (2020) Trends. Immunol. https://doi.org/10.1016/j.it.2020.03.007.
9. Ortega, J.T. et al. (2020) EXCLI J. 19:410.
10. Wrapp, D. et al. (2020) Science 367:1260.
11. Tai, W. et al. (2020) Cell. Mol. Immunol. https://doi.org/10.1016/j.it.2020.03.007.
12. Okba, N. M. A. et al. (2020). Emerg. Infect. Dis. https://doi.org/10.3201/eid2607.200841.
13. Wang, X. et al. (2020) https://doi.org/10.1038/s41423-020-0424-9.
14. Wang, K. et al. (2020) bioRxiv https://www.biorxiv.org/content/10.1101/2020.03.14.988345v1.

Limitations

This product is for research use only and is not approved for use in humans or in clinical diagnosis. Primary Antibodies are guaranteed for 1 year from date of receipt.

Bioinformatics

• Uniprot:
  • AAA51948()