Structure of the IL3 receptor

Molecular biology of the murine IL-3 receptor

Using an antibody (Aic2) that partially blocked IL-3 binding to murine cells, a cDNA termed AIC2A was cloned that encoded an 878 amino acid protein including a signal sequence. The mature protein is a glycoprotein of about 120 kDa. The AIC2A protein is a member of the type I cytokine receptor super-family that includes the (3 and 7 subunits of the IL-2 receptor, the receptors for IL-4 through IL-7, IL-9, GM-CSF, G-CSF, erythropoietin, leukemia inhibitory factor, oncostatin M, and ciliary neurotrophic factor. They have a common structural motif in their extracellular domains. This motif contains approximately 200 amino acids with fibronectin type III modules. Each module contains seven antiparallel 3 strands. There are four conserved cysteines in the N-terminal module and a unique tryptophan-serine-variable amino acid-tryptophan-serine (WSXWS) motif in the C-terminal module.

The AIC2A protein binds murine IL-3 with very low affinity (iid = 10-20 nM). These binding characteristics are consistent with the low-affinity binding site on murine cells. A second cDNA was subsequently cloned that conferred high-affinity IL-3 binding in cooperation with AIC2A. The cDNA was termed SUT-1 and coded for a protein of 396 amino acids that is also a member of the type I cytokine receptor superfamily. The mature protein is about 70 kDa and binds IL-3 with a Kit of 40 n.M. Coex-pression of SUT-1 and AIC2A reconstitutes a receptor that binds murine IL-3 with a Kd of 300 pM. Thus, SUT-1 is now referred to as the a or ligand-binding subunit, and AIC2A as the 3 subunit of the murine IL-3 receptor. Further expression cloning using the Aic2 antibody led to the molecular cloning of a second AIC2 cDNA termed AIC2B. This cDN'A encodes a protein of 896 amino acids with 91% homology to AIC2A, and its structure is basically the same as the IL-3 receptor 3 subunit; however, AIC2B binds neither IL-3 nor any other cytokine. Further studies have revealed that AIC2A is a subunit specific to the IL-3 receptor binding complex, and AIC2B is a 3 subunit shared with the GM-CSF reccptor (Figure 1).

Molecular biology of the human IL-3 receptor

Using the AIC2A cDNA as a probe, the human homolog of the murine IL-3 receptor 3 subunit was cloned. The cDNA was termed KH97 and its overall structure was remarkably similar to the AIC2A/ AIC2B proteins. It is about 56% homologous to the amino acid sequence of the murine A1C2 proteins. KH97 has two WSXWS motifs, but does not bind any IL-3 or other cytokines. Expression cloning using a cotransfection strategy with KH97 cDNA allowed the isolation of a cDNA that bound IL-3 with extremely low affinity. This cDNA, termed DUK-1, encodes a protein of 378 amino acids, and the extracellular domain contains a single WSXWS motif. The mature protein is about 70 kDa, and its structure is similar to the murine IL-3 receptor a subunit. The murine and human proteins however, show only about 70% homology at the amino acid level.

Transfection of COS-7 cells with the human IL-3 receptor a cDNA (DUK-1) yielded cells that bound IL-3 with very low affinity (Kd = 100 nM); however.

How To Bolster Your Immune System

How To Bolster Your Immune System

All Natural Immune Boosters Proven To Fight Infection, Disease And More. Discover A Natural, Safe Effective Way To Boost Your Immune System Using Ingredients From Your Kitchen Cupboard. The only common sense, no holds barred guide to hit the market today no gimmicks, no pills, just old fashioned common sense remedies to cure colds, influenza, viral infections and more.

Get My Free Audio Book


Post a comment