- Kulkarni MV, Tettamanzi MC, Murphy JW, Keeler C, Myszka DG, Chayen NE, Lolis EJ, Hodsdon ME
- Two independent histidines, one in human prolactin and one in its receptor, are critical for pH dependent receptor recognition and activation.
- J Biol Chem. 2010 Sep 30.
- Human prolactin (hPRL), a member of the family of hematopoietic cytokines, functions as both an endocrine hormone and autocrine/paracrine growth factor. We have previously demonstrated that recognition of the hPRL receptor (hPRLr) depends strongly on solution acidity over the physiologic range from pH 6 &- 8. The hPRL-receptor binding interface contains four histidines, whose protonation is hypothesized to regulate pH-dependent receptor recognition. Here, we systematically dissect its molecular origin by characterizing the consequences of His to Ala mutations on pH-dependent receptor-binding kinetics, site-specific histidine protonation, and high resolution structures of the intermolecular interface. Thermodynamic modeling of the pH dependence to receptor-binding affinity reveals large changes in site-specific protonation constants for a majority of interface histidines upon complexation. Removal of individual His imidazoles reduces these perturbations in protonation constants, which is most likely explained by the introduction of solvent-filled, buried cavities in the crystallographic structures without inducing significant conformational rearrangements.