A biosensor study indicating that entropy, electrostatics, and receptor glycosylation drive the binding interaction between interleukin-7 and its receptor.

ABSTRACT: The interaction between interleukin-7 (IL-7) and its ?-receptor, IL-7R?, plays fundamental roles in the development, survival, and homeostasis of B- and T-cells. N-Linked glycosylation of human IL-7R? enhances its binding affinity for human IL-7 300-fold versus that of the nonglycosylated receptor through an allosteric mechanism. The N-glycans of IL-7R? do not participate directly in the binding interface with IL-7. This biophysical study involves dissection of the properties of binding of IL-7 to both nonglycosylated and glycosylated forms of the IL-7R? extracellular domain (ECD) as functions of salt, pH, and temperature using surface plasmon resonance (SPR) spectroscopy. Interactions of IL-7 with both IL-7R? variants display weaker binding affinities with increasing salt concentrations primarily reflected by changes in the first on rates of a two-step reaction pathway. The electrostatic parameter of the IL-7-IL-7R? interaction is not driven by complementary charge interactions through residues at the binding interface or N-glycan composition of IL-7R?, but presumably by favorable global charges of the two proteins. van't Hoff analysis indicates both IL-7-IL-7R? interactions are driven by large favorable entropy changes and smaller unfavorable (nonglycosylated complex) and favorable (glycosylated complex) enthalpy changes. Eyring analysis of the IL-7-IL-7R? interactions reveals different reaction pathways and barriers for the transition-state thermodynamics with the enthalpy and entropy changes of IL-7 binding to nonglycosylated and glycosylated IL-7R?. There were no discernible heat capacity changes for the equilibrium or transition-state binding thermodynamics of the IL-7-IL-7R? interactions. The results suggest that the unbound nonglycosylated IL-7R? samples an extensive conformational landscape relative to the unbound glycosylated IL-7R?, potentially explaining the switch from a "conformationally controlled" reaction (k(1) ? 10(2) M(-1) s(-1)) for the nonglycosylated interaction to a "diffusion-controlled" reaction (k(1) ? 10(6) M(-1) s(-1)) for the glycosylated interaction. Thus, a large favorable entropy change, a global favorable electrostatic component, and glycosylation of the receptor, albeit not at the interface, contribute significantly to the interaction between IL-7 and the IL-7R? ECD.

SUBMITTER: Walsh ST 

PROVIDER: S-EPMC3005950 | biostudies-literature | 2010 Oct

REPOSITORIES: biostudies-literature