title: 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 α-receptor, IL-7Rα, plays fundamental roles in the development, survival, and homeostasis of B- and T-cells. N-Linked glycosylation of human IL-7Rα 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-7Rα 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-7Rα extracellular domain (ECD) as functions of salt, pH, and temperature using surface plasmon resonance (SPR) spectroscopy. Interactions of IL-7 with both IL-7Rα 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-7Rα interaction is not driven by complementary charge interactions through residues at the binding interface or N-glycan composition of IL-7Rα, but presumably by favorable global charges of the two proteins. van't Hoff analysis indicates both IL-7-IL-7Rα 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-7Rα 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-7Rα. There were no discernible heat capacity changes for the equilibrium or transition-state binding thermodynamics of the IL-7-IL-7Rα interactions. The results suggest that the unbound nonglycosylated IL-7Rα samples an extensive conformational landscape relative to the unbound glycosylated IL-7Rα, 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-7Rα ECD.
authors.affiliation: Department of Cell Biology and Molecular Genetics, Institute for Bioscience and Biotechnology Research, W. M. Keck Laboratory for Structural Biology, University of Maryland, 9600 Gudelsky Drive, Rockville, Maryland 20850, USA. swalsh12@umd.edu
authors.forename: Scott T R
authors.initials: ST
authors.lastname: Walsh
mesh_terms: D015374:Biosensing Techniques; D019277:Entropy; D006031:Glycosylation; D006801:Humans; D015851:Interleukin-7 / Q000737:chemistry / Q000378:metabolism*; D008958:Models, Molecular; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D020395:Receptors, Interleukin-7 / Q000737:chemistry / Q000378:metabolism*; D012965:Sodium Chloride / Q000378:metabolism; D055672:Static Electricity
chemical_list: D015851:Interleukin-7; D020395:Receptors, Interleukin-7; C415350:interleukin-7 receptor, alpha chain; D012965:Sodium Chloride
references.citation: Cell. 1999 Apr 16;97(2):271-81
references.pmid: 10219247
references.citation: Proc Natl Acad Sci U S A. 2009 Mar 3;106(9):3131-6
references.pmid: 19204290
references.citation: Adv Protein Chem. 2004;68:147-69
references.pmid: 15500861
references.citation: Adv Protein Chem. 1992;43:313-61
references.pmid: 1442323
references.citation: Curr Opin Struct Biol. 2008 Aug;18(4):499-506
references.pmid: 18638552
references.citation: Curr Opin Struct Biol. 2002 Feb;12(1):41-7
references.pmid: 11839488
references.citation: Nature. 2005 Sep 29;437(7059):640-7
references.pmid: 16193038
references.citation: Methods Enzymol. 2000;323:177-207
references.pmid: 10944753
references.citation: Nat Struct Biol. 2000 Jul;7(7):537-41
references.pmid: 10876236
references.citation: Chem Rev. 2009 Mar 11;109(3):839-60
references.pmid: 19196002
references.citation: Acta Crystallogr Sect F Struct Biol Cryst Commun. 2007 Oct 1;63(Pt 10):865-9
references.pmid: 17909291
references.citation: Biochemistry. 1997 Jan 7;36(1):204-13
references.pmid: 8993335
references.citation: J Biol Chem. 1995 Apr 21;270(16):9459-71
references.pmid: 7721873
references.citation: Proc Natl Acad Sci U S A. 1989 Jan;86(1):302-6
references.pmid: 2643102
references.citation: J Mol Biol. 1999 May 28;289(1):57-67
references.pmid: 10339405
references.citation: Science. 1994 Feb 11;263(5148):777-84
references.pmid: 8303294
references.citation: Protein Sci. 1995 Oct;4(10):2138-48
references.pmid: 8535251
references.citation: J Mol Recognit. 2006 Sep-Oct;19(5):389-407
references.pmid: 16897812
references.citation: Proc Natl Acad Sci U S A. 2004 Dec 7;101(49):17078-83
references.pmid: 15563602
references.citation: J Mol Recognit. 1998 Winter;11(1-6):204-10
references.pmid: 10076841
references.citation: Anal Biochem. 1995 May 1;227(1):176-85
references.pmid: 7668379
references.citation: Nat Immunol. 2002 Jul;3(7):605-7
references.pmid: 12087416
references.citation: Angew Chem Int Ed Engl. 2000 Aug 18;39(16):2834-2846
references.pmid: 11027984
references.citation: J Biol Chem. 1998 Aug 14;273(33):21374-9
references.pmid: 9694899
references.citation: Biochemistry. 1989 Aug 22;28(17):6857-63
references.pmid: 2819038
references.citation: Chem Rev. 1996 Mar 28;96(2):683-720
references.pmid: 11848770
references.citation: Nature. 1998 Oct 1;395(6701):511-6
references.pmid: 9774108
references.citation: Structure. 2009 Jan 14;17(1):54-65
references.pmid: 19141282
references.citation: Proc Natl Acad Sci U S A. 2009 Feb 24;106(8):2559-64
references.pmid: 19196954
references.citation: Br J Cancer. 2001 Apr;84 Suppl 1:3-10
references.pmid: 11308268
references.citation: Q Rev Biophys. 1978 May;11(2):103-78
references.pmid: 353875
references.citation: Proc Natl Acad Sci U S A. 2001 Aug 28;98(18):10037-41
references.pmid: 11517324
references.citation: Curr Opin Biotechnol. 1996 Aug;7(4):409-16
references.pmid: 8768899
references.citation: Nat Rev Immunol. 2009 Jul;9(7):480-90
references.pmid: 19543225
references.citation: Protein Sci. 2003 Sep;12(9):1960-70
references.pmid: 12930995
references.citation: Chem Rev. 1997 Aug 5;97(5):1233-1250
references.pmid: 11851449
references.citation: J Biol Chem. 1990 Mar 15;265(8):4483-91
references.pmid: 2155231
references.citation: Biochemistry. 2002 Dec 10;41(49):14524-31
references.pmid: 12463751
references.citation: Adv Protein Chem. 1995;47:307-425
references.pmid: 8561051
references.citation: Lymphat Res Biol. 2006;4(2):83-100
references.pmid: 16808670
references.citation: J Mol Biol. 1999 Mar 26;287(2):409-19
references.pmid: 10080902
references.citation: J Biol Chem. 1995 Nov 17;270(46):27845-51
references.pmid: 7499256
references.citation: Methods Enzymol. 1998;295:294-315
references.pmid: 9750224
references.citation: Eur J Biochem. 1996 Aug 15;240(1):252-61
references.pmid: 8797861
references.citation: Trends Biochem Sci. 1998 Apr;23(4):149-50
references.pmid: 9584619
references.citation: Trends Biochem Sci. 2006 Mar;31(3):156-63
references.pmid: 16473013
references.citation: Nat Genet. 1998 Dec;20(4):394-7
references.pmid: 9843216
references.citation: Biophys J. 1996 Oct;71(4):2049-55
references.pmid: 8889179
references.citation: J Mol Biol. 2005 Feb 18;346(2):533-50
references.pmid: 15670602
references.citation: Cell. 2008 Jan 25;132(2):259-72
references.pmid: 18243101
references.citation: Nat Rev Immunol. 2007 Feb;7(2):144-54
references.pmid: 17259970
references.citation: J Mol Biol. 1998 May 22;278(5):1015-24
references.pmid: 9600858
references.citation: Nat Struct Biol. 1996 May;3(5):427-31
references.pmid: 8612072
references.citation: Anal Biochem. 2005 Feb 15;337(2):289-93
references.pmid: 15691509