Abstract
Interactions of recombinant soluble prolactin receptors-extracellular domains (PRLR-ECDs) from rabbit, rat, and cow and human growth hormone receptor ECD with immobilized human growth hormone, several prolactins, and bovine placental lactogen were studied utilizing surface plasmon resonance. This method enables real-time kinetic measurements of the interactions and calculations of kinetic constants and of the stoichiometry of interaction, even in cases where only transient interactions occur. In contrast to gel filtration or crystallographic studies, where in most cases the interaction of PRLR-ECDs with various lactogenic hormones indicated formation of 1:1 complexes, our surface plasmon resonance experiments indicated in all cases the transient formation of a 2:1 complex. In most of the interactions the 2:1 complex was very unstable and underwent rapid dissociation to a 1:1 complex. This situation was particularly characteristic of homologous interactions involving hormone and receptor from the same species and was mainly attributed to increased dissociation constants. We suggest that as in the case of growth hormone PRLR activation occurs via hormone-induced transient homodimerization of the receptor, lasting only a few seconds, and that this may be sufficient to initiate the biological signal. Once the signal is initiated, the receptor dimer is no longer required. Its rapid dissociation to a 1:1 complex or to its components may even be advantageous in that it permits activation of additional receptors.
Highlights
Prolactin (PRL)1 and growth hormone (GH) receptors (R) belong to the large cytokine receptor family, which is characterized by a conserved 200 –240-amino acid sequence in the extracellular domain (ECD) [1,2,3]
Optimization of the Immobilization Procedure—Initially, rb, r, and bPRLR-ECDs were immobilized via their single free cysteine residue
An alternative protocol was employed to overcome this difficulty; the respective hormones were immobilized via their amino groups. This method yielded promising results; in all cases, the immobilized hormones retained a high capacity of interaction with soluble PRLR-ECDs or, in the case of hGH, with hGHR-ECD
Summary
Prolactin (PRL)1 and growth hormone (GH) receptors (R) belong to the large cytokine receptor family, which is characterized by a conserved 200 –240-amino acid sequence in the extracellular domain (ECD) [1,2,3]. Interaction of bPRLR-ECD with oPRL, bPL, and hGH indicated formation of an apparent 1:1 complex as determined by both SPR (Fig. 1B and Table II) and gel filtration [21].
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