tailieunhanh - Báo cáo khoa học: Thermodynamic characterization of interleukin-8 monomer binding to CXCR1 receptor N-terminal domain

Chemokines elicit their function by binding receptors of the G-protein-cou-pled receptor class, and the N-terminal domain (N-domain) of the receptor is one of the two critical ligand-binding sites. In this study, the thermo-dynamic basis for binding of the chemokine interleukin-8 (IL-8) to the N-domain of its receptor CXCR1 was characterized using isothermal titra-tion calorimetry. | ỊFEBS Journal Thermodynamic characterization of interleukin-8 monomer binding to CXCR1 receptor N-terminal domain Harshica Fernando1 Gregg T. Nagle2 and Krishna Rajarathnam1 1 Department of Biochemistry and Molecular Biology University of Texas MedicalBranch Galveston TX USA 2 Department of Neuroscience and Cell Biology University of Texas MedicalBranch Galveston TX USA Keywords interleukin-8 isothermal titration calorimetry monomer N-terminaldomain thermodynamics Correspondence K. Rajarathnam MRB UTMB Galveston TX 77555-1055 USA Fax 1 409 772 1790 Tel 1 409 772 2238 E-mail krrajara@ Received 25 August 2006 revised 2 November 2006 accepted 7 November 2006 doi Chemokines elicit their function by binding receptors of the G-protein-cou-pled receptor class and the N-terminal domain N-domain of the receptor is one of the two critical ligand-binding sites. In this study the thermodynamic basis for binding of the chemokine interleukin-8 IL-8 to the N-domain of its receptor CXCR1 was characterized using isothermal titration calorimetry. We have shown previously that only the monomer of IL-8 and not the dimer functions as a high-affinity ligand so in this study we used the IL-8 1-66 deletion mutant which exists as a monomer. Calorimetry data indicate that the binding is enthalpically favored and entropical-ly disfavored and a negative heat capacity change indicates burial of hydrophobic residues in the complex. A characteristic feature of chemokine receptor N-domains is the large number of acidic residues and experiments using different buffers show no net proton transfer indicating that the CXCR1 N-domain acidic residues are not protonated in the binding process. CXCR1 N-domain peptide is unstructured in the free form but adopts a more defined structure in the bound form and so binding is coupled to induction of the structure of the N-domain. Measurements in the presence of the osmolyte trimethylamine N-oxide which induces the