• Purity

  >90%, by SDS-PAGE under reducing conditions and visualized by silver stain

• Endotoxin Level

  <1.0 EU per 1 μg of the protein by the LAL method.  

• Activity

  Measured by its ability to inhibit the IL-3-induced proliferation of NFS‑60 mouse myelogenous leukemia lymphoblast cells. The ED    ₅₀ for this effect is 0.03‑0.15 µg/mL in the presence of 2.5 µg/mL Recombinant Mouse IL‑3 R beta Fc Chimera (Catalog # ) and 2 ng/mL of Recombinant Mouse IL‑3 (Catalog # ).

• Source

  Spodoptera frugiperda,     Sf 21 (baculovirus)-derived

  Mouse IL-3 R alpha (Ser17-Lys331) Accession # P26952	IEGRID	Human IgG1 (Pro100-Lys330)
  N-terminus		C-terminus

• Accession #

• N-terminal Sequence    
  Analysis

  Ser17

• Structure / Form

  Disulfide-linked homodimer

• Predicted Molecular Mass

  61.0 kDa (monomer)

• SDS-PAGE

  70-80 kDa, reducing conditions

Background: IL-3 R alpha/CD123

The IL-3 receptor chain (IL‑3 R alpha ; also SUT-1 and CD123) is a 60‑70 kDa member of the class I cytokine receptor family of proteins (1, 2, 3). Members of this class are type I transmembrane proteins that contain two fibronectin type III (FNIII) modules and a distinctive Trp‑Ser‑x‑Trp‑Ser peptide motif in the extracellular domain. This is in contrast to class II receptors that share the same fibronectin domains but lack both the WSxWS motif and analogous cysteine spacings. Mouse IL‑3 R alpha is synthesized as a 396 amino acid (aa) precursor that contains a 16 aa signal sequence, a 315 aa extracellular region, a 24 aa transmembrane segment, and a 41 aa cytoplasmic tail (3, 4). The molecule is expressed on multiple cell types, including endothelial cells (5), monocytes (6), eosinophils (7), basophils plus mast cells (8), and plasmacytoid CD4  ⁺ T cells (9). IL‑3 R alpha serves as a low affinity binding protein for 24‑28 kDa monomeric IL‑3 (1, 3, 4, 10, 11). Following binding, the IL‑3:IL‑3 R alpha complex likely interacts with a preformed signaling homodimer comprised of either 120 kDa AIC2A (= beta   _IL-3) or 130 kDa AIC2B (= beta c) chains. This tetramer appears to recruit one more IL‑3:IL‑3 R alpha complex, generating a fully functional hexamer (1, 3, 4, 12, 13). Signaling is mediated by receptor‑associated cytoplasmic kinases, as class I cytokine receptors do not possess intrinsic kinase activity. Notably, the IL‑3 R complex may not exist as a singularity, but actually form higher‑order complexes with FcR gamma, beta   ₁ integrin, and VEGF R2 (1). There are at least two IL‑3 Ra isoform variants in mouse. One is found in the AKR and A/J strains, and shows a deletion of aa 274‑283. This is not present at the cell membrane (14). The second (called SP2) shows a deletion of aa 20‑112, generating a 50‑55 kDa membrane form that binds IL‑3, but will only signal through beta   _IL-3 (15, 16). IL‑3’s choice of full‑length IL‑3 R alpha (SP1) or SP2 leads to different signaling outcomes, presumably due to the engagement of different binding sites on beta   _IL-3. The extracellular domain of mouse IL‑3 R alpha /SP1 shares only 44% and 29% aa sequence identity with rat and human IL‑3 R alpha, respectively. Nevertheless, human IL‑3 is reported to be active on the mouse receptor complex that is expressed on select cell types (17).

• References:

1. Broughton, S.E. et al. (2012) Immunol. Rev. 250:277.

2. Langer, J.A. et al. (2004) Cytokine Growth Factor Rev. 15:33.

3. Miyajima, A. et al. (1993) Blood 82:1960.

4. Hara, T. & A. Miyajima (1992) EMBO J. 11:1875.

5. Korpelainen, E.I. et al. (1993) Proc. Natl. Acad. Sci. USA 90:11137.

6. Ebner, S. et al. (2002) J. Immunol. 168:6199.

7. Gregory, B. et al. (2003) J. Immunol. 170:5359.

8. Dahl, C. et al. (2004) Allergy 59:1087.

9. Grouard, G. et al. (1997) J. Exp. Med. 185:1101.

10. Clark-Lewis, I. et al. (1984) J. Biol. Chem. 259:7488.

11. Knepper, T.P. et al. (1992) Biochemistry 31:11651.

12. Ogorochi, T. et al. (1992) Blood 79:895.

13. Murphy, J.M. et al. (2004) J. Biol. Chem. 279:26500.

14. Ichihara, M. et al. (1995) EMBO J. 14:939.

15. Chen, J. et al. (2009) J. Biol. Chem. 284:5763.

16. Mirza, S. et al. (2010) J. Biol. Chem. 285:22370.

17. Dentelli, P. et al. (1999) J. Immunol. 163:2151.

• Long Name:

  Interleukin 3 Receptor alpha

• Entrez Gene IDs:

  3563 (Human); 16188 (Mouse)

• Alternate Names:

  CD123 antigen; CD123; hIL3Ra; hIL-3Ra; IL-3 R alpha; IL-3 receptor subunit alpha; IL3R alpha; IL-3R subunit alpha; IL3R; IL3RA; IL-3Ra; IL-3R-alpha; IL3RAY; IL3RX; IL3RY; interleukin 3 receptor, alpha (low affinity); interleukin-3 receptor subunit alpha; MGC34174