Ligand Selectivity and Affinity of Chemokine Receptor CXCR1

Abstract

Glu-Leu-Arg (“ELR”) CXC chemokines interleukin-8 (IL-8) and melanoma growth stimulatory activity (MGSA) recruit neutrophils by binding and activating two receptors, CXCR1 and CXCR2. CXCR1 is specific, binding only IL-8 with nanomolar affinity, whereas CXCR2 is promiscuous, binding all ELRCXC chemokines with high affinity. Receptor signaling consists of two events: interactions between the ligand N-terminal loop (N-loop) and receptor N-terminal domain (N-domain) residues (site I), and between the ligand N-terminal ELR and the receptor juxtamembrane domain (J-domain) residues (site II). It is not known how these interactions mediate ligand affinity and selectivity, and whether binding at one site influences binding and function at the other. Sequence analysis and structure-function studies have suggested that the receptor N-domain plays an important role in ligand selectivity. Here, we report ligand-binding properties and structural characteristics of the CXCR1 N-domain in solution and in detergent micelles that mimic the native membrane environment. We find that IL-8 binds the N-domain with significantly higher affinity in micelles than in solution (∼1 μm versus ∼20 μm) and that MGSA does not bind the N-domain in solution but does in micelles with appreciable affinity (∼3 μm). We find that the N-domain is structured in micelles and that the entire N-domain interacts with the micelle in an extended fashion. We conclude that the micellar environment constrains the N-domain, and this conformational restraint influences its ligand-binding properties. Most importantly, our data suggest that for both ligands, site I interaction provides similar affinity and that differential coupling between site I and II interactions is responsible for the observed differences in affinity. Glu-Leu-Arg (“ELR”) CXC chemokines interleukin-8 (IL-8) and melanoma growth stimulatory activity (MGSA) recruit neutrophils by binding and activating two receptors, CXCR1 and CXCR2. CXCR1 is specific, binding only IL-8 with nanomolar affinity, whereas CXCR2 is promiscuous, binding all ELRCXC chemokines with high affinity. Receptor signaling consists of two events: interactions between the ligand N-terminal loop (N-loop) and receptor N-terminal domain (N-domain) residues (site I), and between the ligand N-terminal ELR and the receptor juxtamembrane domain (J-domain) residues (site II). It is not known how these interactions mediate ligand affinity and selectivity, and whether binding at one site influences binding and function at the other. Sequence analysis and structure-function studies have suggested that the receptor N-domain plays an important role in ligand selectivity. Here, we report ligand-binding properties and structural characteristics of the CXCR1 N-domain in solution and in detergent micelles that mimic the native membrane environment. We find that IL-8 binds the N-domain with significantly higher affinity in micelles than in solution (∼1 μm versus ∼20 μm) and that MGSA does not bind the N-domain in solution but does in micelles with appreciable affinity (∼3 μm). We find that the N-domain is structured in micelles and that the entire N-domain interacts with the micelle in an extended fashion. We conclude that the micellar environment constrains the N-domain, and this conformational restraint influences its ligand-binding properties. Most importantly, our data suggest that for both ligands, site I interaction provides similar affinity and that differential coupling between site I and II interactions is responsible for the observed differences in affinity. Chemokines, or chemotactic cytokines, are small soluble proteins (70–120 residues) that play fundamental regulatory roles in native immunity, inflammation, and host defense against infection. Over 40 chemokines have been identified to date, and these can be classified as CC, CXC, C, or CX3C chemokines based on the position of conserved cysteines (1Murphy P.M. Baggiolini M. Charo I.F. Hebert C.A. Horuk R. Matsushima K. Miller L.H. Oppenheim J.J. Power C.A. Pharmacol. Rev. 2000; 52: 145-176PubMed Google Scholar). The CXC chemokines can be further classified as Glu-Leu-Arg (“ELR”) and “non-ELR”, based on the presence or absence of this motif before the first cysteine. Chemokines carry out their function by binding and activating receptors that belong to the G-protein-coupled receptor (GPCR) 1The abbreviations used are: GPCR, G-protein-coupled receptor; CXCR1, CXC chemokine receptor 1; CXCR2, CXC chemokine receptor 2; IL-8, interleukin-8; MGSA, melanoma growth stimulatory activity; N-domain, N-terminal domain; CD, circular dichroism; hCXCR1, human CXCR1; rCXCR1, rabbit CXCR1; DPC, dodecylphosphocholine; NBS, N-bromosuccinimide; LIC, ligation-independent cloning.1The abbreviations used are: GPCR, G-protein-coupled receptor; CXCR1, CXC chemokine receptor 1; CXCR2, CXC chemokine receptor 2; IL-8, interleukin-8; MGSA, melanoma growth stimulatory activity; N-domain, N-terminal domain; CD, circular dichroism; hCXCR1, human CXCR1; rCXCR1, rabbit CXCR1; DPC, dodecylphosphocholine; NBS, N-bromosuccinimide; LIC, ligation-independent cloning. superfamily. The “ELRCXC” chemokines bind two receptors, CXCR1 and CXCR2, on the neutrophil cell surface. Interleukin-8 (IL-8, also known as CXCL8) binds both neutrophil receptors with high affinity, whereas other ELRCXC chemokines, including melanoma growth stimulatory activity (MGSA, also known as CXCL1), bind only CXCR2 with high affinity (2Ahuja S.K. Lee J.C. Murphy P.M. J. Biol. Chem. 1996; 271: 225-232Abstract Full Text Full Text PDF PubMed Scopus (135) Google Scholar, 3Murphy P.M. Semin. Hematol. 1997; 34: 311-318PubMed Google Scholar). The chemokine-chemokine receptor system in general is intricately complex, with multiple ligands binding a single receptor and a single ligand binding multiple receptors within, and sometimes outside, the respective subfamily (4Locati M. Murphy P.M. Annu. Rev. Med. 1999; 50: 425-440Crossref PubMed Scopus (251) Google Scholar, 5Loetscher P. Clark-Lewis I. J. Leukoc. Biol. 2001; 69: 881-884PubMed Google Scholar). The structural and thermodynamic basis for the differences seen in ligand binding affinities, receptor selectivities, activation, and downstream signaling of chemokine receptors is not known. Knowledge of ligand and receptor structures, of binding-induced structural and dynamic changes in the ligand and receptor, and of the energetic basis of the ligand-receptor interaction is thus essential to understand this differential affinity and selectivity. The structures of several chemokines, including ELRCXC chemokines such as IL-8 and MGSA, are known, and all adopt a common chemokine fold: a disordered N-terminal end, followed by a series of loops and turns (defined as the N-loop), three β-strands, and an overlying α-helix (6Clore G.M. Bax A. Driscoll P.C. Wingfield P.T. Gronenborn A.M. Biochemistry. 1990; 29: 8172-8184Crossref PubMed Scopus (192) Google Scholar, 7Baldwin E.T. Weber I.T. St. Charles R. Xuan J.C. Appella M. Matsushima K. G.M. Gronenborn A.M. A. A. PubMed Scopus Google Scholar, J. Horuk R. J. Biol. PubMed Scopus Google Scholar, Clark-Lewis I. J. Biol. Chem. Full Text PDF PubMed Google Scholar, K. Clark-Lewis I. Biochemistry. 34: PubMed Scopus Google Scholar, Annu. Rev. Pharmacol. PubMed Scopus Google Scholar). receptors are classified the chemokine as and based on the of bind (1Murphy P.M. Baggiolini M. Charo I.F. Hebert C.A. Horuk R. Matsushima K. Miller L.H. Oppenheim J.J. Power C.A. Pharmacol. Rev. 2000; 52: 145-176PubMed Google Scholar, R. Rev. 2001; PubMed Scopus Google Scholar). are 40 chemokines, are receptors CXC, CC, and The structures of chemokine receptors are not the only to is that of K. C.A. I. M. M. 2000; PubMed Scopus Google Scholar). studies are the structural basis of the ligand and binding affinity of CXCR1 for IL-8 versus the of CXCR1 and the of CXCR2, the seen on a in the entire The structural basis of IL-8 and MGSA function been both and Horuk R. K. J. J. Google Scholar, I. Baggiolini M. J. Biol. Chem. Full Text PDF PubMed Google Scholar, I. M. Baggiolini M. J. Biol. Chem. Full Text PDF PubMed Google Scholar, I. K. Baggiolini M. J. Leukoc. Biol. PubMed Scopus Google Scholar, J. Miller L.H. Horuk R. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, J. Biol. Chem. 1996; 271: Full Text Full Text PDF PubMed Scopus Google Scholar, Baggiolini M. Clark-Lewis I. J. Biol. Chem. Full Text PDF PubMed Google Scholar, M. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, I. J. Biol. Chem. 1996; 271: Full Text Full Text PDF PubMed Scopus Google Scholar, K. J. J. Biol. Chem. 1999; Full Text Full Text PDF PubMed Scopus Google Scholar). and similar studies for other chemokines, that the receptor signaling two interaction between the ligand N-terminal loop (N-loop) and the receptor N-terminal domain residues (site and between the ligand N-terminal and the receptor and (J-domain) residues (site P. K. A. Baggiolini M. Clark-Lewis I. J. 1997; PubMed Scopus Google Scholar, Charo I.F. J. Biol. Chem. 1996; 271: Full Text Full Text PDF PubMed Scopus Google Scholar). these interactions mediate ligand affinity, receptor selectivity, and receptor activation, and whether binding at one site influences at the other site are not known. IL-8 binds both CXCR1 and CXCR2 with high affinity whereas MGSA binds CXCR2 with high affinity and CXCR1 with affinity J. Biol. Chem. 1996; 271: Full Text Full Text PDF PubMed Scopus Google Scholar, Clark-Lewis I. Baggiolini M. J. Biol. Chem. 1997; Full Text Full Text PDF PubMed Scopus Google Scholar). IL-8 and MGSA have similar such as high similar of to and similar and studies in IL-8 and MGSA have identified ELR and the residues as important for receptor binding and IL-8 and MGSA ELR binding and and in been bind with affinity and are J. Miller L.H. Horuk R. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, Baggiolini M. Clark-Lewis I. J. Biol. Chem. Full Text PDF PubMed Google Scholar, I. Baggiolini M. A. PubMed Scopus Google Scholar). the other and studies that the residues are in receptor binding and receptor versus residues in IL-8 are responsible for high affinity binding to both receptors and in MGSA are responsible for high and affinity binding to CXCR2 and CXCR1, J. Biol. Chem. 1996; 271: Full Text Full Text PDF PubMed Scopus Google Scholar, I. J. Biol. Chem. 1996; 271: Full Text Full Text PDF PubMed Scopus Google Scholar). of the IL-8 and MGSA structures conformational differences for the that the differences in this be responsible for the receptor J. Horuk R. J. Biol. PubMed Scopus Google Scholar). suggest that the differential binding of IL-8 and MGSA to CXCR1 is not to differences in their properties but to differences in residues or structural of the two The for IL-8 have also that the residues are dynamic than the Gronenborn A.M. G.M. J. Biol. PubMed Scopus Google Scholar). the basis of structure-function studies on IL-8, been that the of chemokine ligand as a to the N-terminal ELR and the residues are for interaction with the receptors I. K. Baggiolini M. J. Leukoc. Biol. PubMed Scopus Google Scholar, K. Clark-Lewis I. Biochemistry. PubMed Scopus Google Scholar, K. Baggiolini M. Clark-Lewis I. Biochemistry. 1999; PubMed Scopus Google Scholar). The structural of the receptor residues for binding and are than for the to that residues the receptor N-domain and the mediate binding and activation, but is not how these interactions mediate affinity and receptor selectivity. studies have identified of the CXCR1 and CXCR2 residues as important for IL-8 on the basis of binding and receptor activity C.A. A. M. J. Horuk R. J. Biol. Chem. Full Text PDF PubMed Google Scholar, Hebert C.A. J. Biol. Chem. Full Text PDF PubMed Google Scholar, A. 2000; PubMed Scopus Google Scholar, J. A. Pharmacol. PubMed Scopus Google Scholar). of CXCR1 and CXCR2, and with suggest that the two receptors are not and with IL-8 and MGSA in a differential (2Ahuja S.K. Lee J.C. Murphy P.M. J. Biol. Chem. 1996; 271: 225-232Abstract Full Text Full Text PDF PubMed Scopus (135) Google Scholar, J. Biol. Chem. Full Text PDF PubMed Google Scholar, J. Biol. Chem. 1996; 271: Full Text Full Text PDF PubMed Scopus Google Scholar, R. M. J. J. Biol. Chem. Full Text PDF PubMed Google Scholar, J. J. Biol. Chem. Full Text PDF PubMed Google Scholar). studies that the N-domain plays an important role in ligand binding but suggest roles for the N-domain in receptor (2Ahuja S.K. Lee J.C. Murphy P.M. J. Biol. Chem. 1996; 271: 225-232Abstract Full Text Full Text PDF PubMed Scopus (135) Google Scholar, J. Biol. Chem. Full Text PDF PubMed Google Scholar, R. M. J. J. Biol. Chem. Full Text PDF PubMed Google Scholar, J. J. Biol. Chem. Full Text PDF PubMed Google Scholar). Sequence analysis of CXCR1 and CXCR2 receptors that the N-domain is the conserved and the as to between the entire The for the of the N-domain the that IL-8 binds the receptor with appreciable affinity and IL-8 binding to the receptor J. Biol. Chem. Full Text PDF PubMed Google Scholar, I. Med. Chem. 1996; Scopus Google Scholar, G.M. Gronenborn A.M. PubMed Scopus Google Scholar, 1999; Full Text Full Text PDF Scopus Google Scholar). the structural characteristics and ligand-binding properties of the N-domain the structural and energetic basis of and affinity of the this we have used and circular to the structural properties of the CXCR1 N-domain and to these with the ligand and affinity of CXCR1 for IL-8 versus We find that the CXCR1 N-domain is structured in detergent micelles that mimic the membrane environment and binds both IL-8 and MGSA with similar affinity. We the of these in the of the structural and thermodynamic basis of ligand binding affinity and selectivity. and of N-domain rabbit CXCR1 receptor been to bind human IL-8 with affinity and similar to that of the human CXCR1 J. Biol. Chem. Full Text PDF PubMed Google Scholar, R. M. J. J. Biol. Chem. Full Text PDF PubMed Google The human and rabbit receptor high and both bind IL-8 with similar affinity J. Biol. Chem. Full Text PDF PubMed Google Scholar). The CXCR1 N-domain are in Sequence 1; residues identified as important for ligand binding are in We of both human and rabbit CXCR1 and that the rabbit to and We have used of the N-domain for our structural and binding The entire N-domain observed to be soluble in and we used two and residues of the on the N-terminal end, and these have been not essential for binding I. Med. Chem. 1996; Scopus Google Scholar). the membrane residues on the of the The for the a that to in Sequence to to We also a for as a to that the binding to the native is N-domain in the of or at The by on a a of and and by and of IL-8 and human IL-8 as a the IL-8 at the ligation-independent site The in in the presence of to an of and with for at The and by followed by The the a and The and The and by a of in The the and at further MGSA the and and as in and on a with at and to at in Receptor used at a of by in to a of The micelle for in and in of the IL-8 out in a of to a solution of μm IL-8 to a of μm The to for and by in at not in the of MGSA, are in its the ligand binding IL-8 or MGSA in to μm with or a μm) of N-domain of the IL-8 or MGSA of the ligand N-domain or for IL-8 but appreciable at The ligand binding studies in micelles out in a similar but The at studies in and at studies in and against ligand to binding and to a binding the the of versus in and on an at in of the receptor N-domain in this and to to as an of three and to the studies out in the presence of in the of in the μm in of receptor N-domain and ligand and of the to in a of the ligand and receptor and of the to in a by of the N-domain and be in the of and studies also out in of IL-8 and MGSA to CXCR1 N-domain in have used circular to the binding of IL-8 and MGSA to the and N-domain and the and observed of the The are by the of and the absence of ligand binding to the N-domain the observed of the to the the The observed are the that both bind IL-8 in for MGSA, the and observed absence of interaction and on the environment of and residues) used to structural changes on binding of IL-8 to the The and observed differences in the to and is the of and these data that on the the ligand are in this binding and are in that both the and N-domain bind IL-8 but not MGSA in the binding to IL-8 in the presence of IL-8 not of IL-8 and MGSA to CXCR1 N-domain in the receptor, the N-domain is to the membrane surface. environment conformational on the N-domain, in have on ligand binding affinity the of the such binding studies of the out in the presence of micelles have been used as of the membrane environment in the of membrane the binding studies in of the binding studies in micelles N-domain bind IL-8 in as can be seen the and and structural changes are seen in the to on IL-8 to N-domain in as in solution and in the of MGSA, the that the N-domain does bind this ligand in whereas the does not and is in to in both N-domain not bind that the micellar environment influences the ligand-binding properties of the of N-domain in and in have binding of both IL-8 and MGSA to both N-domain in solution and in micelles The of the N-domain on IL-8 MGSA to in studies that the N-domain binds IL-8 with a of μm in solution whereas the binds with a of μm both N-domain residues important for ligand binding and the residues on the that binding in solution or by the of the in The binding of the to IL-8 in solution be to this to IL-8, MGSA does not binding to in solution and studies have N-domain of and bind IL-8 in solution with μm J. Biol. Chem. Full Text PDF PubMed Google Scholar, I. Med. Chem. 1996; Scopus Google Scholar, 1999; Full Text Full Text PDF Scopus Google Scholar). binding of the and for IL-8 in solution are to these binding We also ligand-binding of the N-domain in the presence of micelles of the N-domain on of the presence of both the and IL-8 with of μm affinity is to higher than the observed affinity of the in MGSA not bind the N-domain in micelles but bind the N-domain in micelles with appreciable affinity μm) We also the binding of IL-8 and MGSA to a both in and micelles and observed interaction that binding characteristics to the native is of N-domain to IL-8 and MGSA in and in is a of three to binding at two in is a of three to binding at two not not not not not not not is a of three to binding at two not in a that the N-domain does bind MGSA in as observed in our that the micellar or native membrane environment influences the properties of the the of μm is similar to that for IL-8 that site I interaction is not the of in of N-domain in the receptor, the N-domain is to the membrane and this to be and than in structures by the N-domain in the native membrane environment are in only is The N-domain be structured structural but and as a or a conformational the ligand binding as observed in our ligand binding understand the of the membrane environment on structural characteristics of the N-domain, we out to of the N-domain interacts with the native membrane that the residues are than the N-terminal residues not is that these residues the N-domain to the membrane and be responsible for in the N-domain in the presence of the membrane environment. It is also that the entire N-domain interacts with the membrane environment. native of the N-domain, we the structural characteristics of the and in have been used as of the membrane environment in the of membrane of their properties of and of with have been used in the structural and of membrane proteins J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar). of studies have that multiple including and interactions and of residues such as to the the the and of the in micelles PubMed Scopus Google Scholar). micelles also have to be used in solution studies of membrane proteins PubMed Scopus Google Scholar). We have used a detergent with an been to be in membrane and J. PubMed Scopus Google Scholar). The and N-domain two the in and in the that the environment of these in micelles of the in solution and in micelles also to structural changes in the N-domain The of both in solution are of whereas in micelles of differences in the environment of the residues in and in micelles for both and is that the changes seen in the environment in the of the the whereas the changes seen in both and the in the of It is also that is of and that all changes seen are to the differential of residues the micelle differences in and in the two studies high further on these We further both and that the only the micelle of interaction of the with the micellar and not with detergent We also observed that the in and of in micelles than observed for the N-domain of and N-domain in solution and out in with or The of and and of and in and micelles are in whereas in and of the N-domain in solution and in micelles thus suggest that the N-domain is structured in micelles that this influences the ligand binding properties of the of the of the and further on the of the N-domain in the of the domain the of in the presence of that interaction with the micelle is not to the residues their absence in the does not the to this interacts with the The characteristics thus that the entire N-domain interacts with the micelle in an extended of the N-domain in the micellar environment with the observed of and of in in our also that the is structured in the presence of micelles not for to CXCR1 structural changes seen in the in the ligand binding studies are in the of the of residues on the ligand or receptor, or is in with that in the of IL-8 with and in the N-domain of M. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, 1999; Full Text Full Text PDF Scopus Google Scholar, C.A. J. M. J. P. J. Biol. Chem. 1996; 271: Full Text Full Text PDF PubMed Scopus Google Scholar). two have been to to and of been to bind in a in the of IL-8 by a of residues that 1999; Full Text Full Text PDF Scopus Google Scholar). The rabbit CXCR1 two and a and to and of the changes in the observed are in the of is that the changes seen are of IL-8, or of the N-domain, or our interactions of and binding in micelles are significantly higher than in that the micellar environment the of the N-domain in binding to is further by the the ligand binding affinity in solution than the both ligand in the presence of micelles with the high affinity (∼1 The by the in to bind ligand with the affinity as the that both the of conformational in micelles of further to this the the N-domain bind MGSA with affinity (∼3 μm) in that MGSA binding residues that are not on the for its interaction with the The that both IL-8 and MGSA the N-domain in micelles with similar affinity that the N-domain is not the of ligand in the binding and function two between the receptor N-domain and ligand residues (site and between receptor the (J-domain) and ligand N-terminal residues (site II). The interaction in receptors that bind and ligands is to have the the receptor seen in receptors that bind small a for of by the binding affinity and of the receptor differential between the two in ligand-receptor The binding affinity can be in of and two are the I), the two interactions are is the with the binding is the with the ligand and receptor N-domain and is the with the ligand ELR and receptor in the binding are is II is the coupling between the coupling be or in the binding at site the for binding at site and in the binding at one site the for binding at the other for both IL-8 and MGSA binding to CXCR1 are known J. Biol. Chem. 1996; 271: Full Text Full Text PDF PubMed Scopus Google Scholar, Clark-Lewis I. Baggiolini M. J. Biol. Chem. 1997; Full Text Full Text PDF PubMed Scopus Google Scholar). and of the ELR residues both in IL-8 and MGSA in to in binding J. Miller L.H. Horuk R. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, Baggiolini M. Clark-Lewis I. J. Biol. Chem. Full Text PDF PubMed Google Scholar, I. Baggiolini M. A. PubMed Scopus Google Scholar). but the of these residues to site II and the binding affinity be to site I interaction Clark-Lewis I. Baggiolini M. J. Biol. Chem. 1997; Full Text Full Text PDF PubMed Scopus Google Scholar, Hebert C.A. J. Biol. Chem. Full Text PDF PubMed Google Scholar). to understand the of the as as to understand the coupling between these we to the interactions similar to seen in the CXCR1 N-domain IL-8 binding to the receptor with an of ∼20 μm J. Biol. Chem. Full Text PDF PubMed Google Scholar, I. Med. Chem. 1996; Scopus Google Scholar). the N-domain is to the membrane we the binding of the ligand to the N-domain in micelles that mimic the native membrane environment. data that both IL-8 and MGSA bind CXCR1 N-domain in micelles with high affinity μm) the of ligand binding to in micelles that a environment. is not multiple receptor residues mediate site II interaction C.A. A. M. J. Horuk R. J. Biol. Chem. Full Text PDF PubMed Google Scholar, Hebert C.A. J. Biol. Chem. Full Text PDF PubMed Google Scholar). can be the binding affinity of a the ELR motif to the studies not that the binding is or in solution to conformational I. Baggiolini M. A. PubMed Scopus Google Scholar). in CXCR1, the N-domain is a to affinity, binding IL-8 and MGSA with a of The that the ELR is conserved and ELR for both ligands in similar in binding that of binding for site II interaction is similar J. Miller L.H. Horuk R. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, Baggiolini M. Clark-Lewis I. J. Biol. Chem. Full Text PDF PubMed Google Scholar, I. Baggiolini M. A. PubMed Scopus Google Scholar). suggest ligand We that is for MGSA, and binding at site I the for binding to site II between the two to a conformational in the ligand or receptor, or ELR and residues are to and further are to the in residues such as in MGSA in high affinity binding but whereas a similar in IL-8 in a in both binding and function Horuk R. K. J. J. Google Scholar, K. J. J. Biol. Chem. 1999; Full Text Full Text PDF PubMed Scopus Google Scholar). the binding also binding to in IL-8 and of in MGSA in in binding and whereas a similar on IL-8 binding and function J. Miller L.H. Horuk R. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, K. Clark-Lewis I. Baggiolini M. 1996; PubMed Scopus Google Scholar). suggest that the ligand structural play a role in coupling the The role of receptor N-domain and the in binding affinity and ligand have been by these between CXCR1 and CXCR2. of the receptor binding and function that be for of the receptors, that receptor also play a role in coupling the interactions (2Ahuja S.K. Lee J.C. Murphy P.M. J. Biol. Chem. 1996; 271: 225-232Abstract Full Text Full Text PDF PubMed Scopus (135) Google Scholar, J. Biol. Chem. Full Text PDF PubMed Google Scholar). our studies that the CXCR1 N-domain a in a micellar and ligand binding out receptor in micelles the characteristics of that domain in the The ligand-binding by the N-domain significantly higher in micelles than in and the structural and energetic basis of IL-8 and MGSA interaction with the receptor N-domain common binding but MGSA at the and the that MGSA binds to the CXCR1 N-domain only in micelles that the of of conformational are for these is the first ligand binding of chemokines to their receptor in micelles and a to at the energetic and structural basis of ligand selectivity, and in this Chemokines and their receptors have been in a of including J.J. Horuk R. Pharmacol. Full Text Full Text PDF PubMed Scopus Google Scholar, K. PubMed Scopus Google Scholar). of the structural and thermodynamic basis for receptor binding is essential for and We for the of IL-8 and for the of the MGSA We also and for and with and We and of the of with