The goal of this work is to understand the structural and biochemical basis for the recruitment of lymphocytes by human Lymphotactin, a chemokine that defies the traditional paradigm by interconverting between two entirely different tertiary structures. Inflammation in the vertebrate immune system is orchestrated by approximately 50 chemokines that specifically activate members of a group of 20 G protein-coupled receptors. These secreted signaling proteins also bind extracellular matrix glycosaminoglycans (GAG) in order to direct migration along a gradient of chemokine concentration. Lymphotactin (Ltn/XCL1), the prototype and single member of the C class of chemokines, acts through its cognate receptor XCR1 to selectively recruit T and NK cells. Functional roles in tumor regression and tissue transplant rejection highlight two disease states that may respond to treatment with either Ltn mimetics or antagonists. Ltn contains only one of the two disulfides conserved in all other chemokines, and is further distinguished by a unique disordered C-terminal extension that is essential for activity. A consequence of these divergent sequence features is that Ltn simultaneously adopts two distinct tertiary structures in physiological solution conditions, only one of which resembles the canonical chemokine fold. Experiments in Specific Aim 1 will use NMR spectroscopy and mutagenesis to determine the novel non-chemokine structure of Ltn, measure the dynamics of interconversion, and test the hypothesis that its conformational equilibrium derives from the lack of a conserved disulfide bridge. The goal of Aim 2 is to alter the conformational equilibrium and measure binding affinities for each species by surface plasmon resonance, in order to test the hypothesis that the structural interconversion creates a high affinity GAG binding site essential for in vivo activity.
In Specific Aim 3, conserved residues in the essential C-terminus will be probed for their role in GPCR activation, and comparisons of activity in vitro and in vivo for conformationally-restricted Ltn variants will be compared in order to test the hypothesis that only the chemokine-like structure is competent to bind and activate the receptor. These structural and biochemical studies are designed to open new avenues for in vivo modulation of lymphocyte trafficking directed by Lymphotactin.

Agency
National Institute of Health (NIH)
Institute
National Institute of Allergy and Infectious Diseases (NIAID)
Type
Research Project (R01)
Project #
3R01AI063325-05S1
Application #
7846710
Study Section
Molecular and Cellular Biophysics Study Section (BBCA)
Program Officer
Nasseri, M Faraz
Project Start
2009-06-05
Project End
2010-09-30
Budget Start
2009-06-05
Budget End
2010-09-30
Support Year
5
Fiscal Year
2009
Total Cost
$45,265
Indirect Cost
Name
Medical College of Wisconsin
Department
Biochemistry
Type
Schools of Medicine
DUNS #
937639060
City
Milwaukee
State
WI
Country
United States
Zip Code
53226
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Fox, Jamie C; Tyler, Robert C; Guzzo, Christina et al. (2015) Engineering Metamorphic Chemokine Lymphotactin/XCL1 into the GAG-Binding, HIV-Inhibitory Dimer Conformation. ACS Chem Biol 10:2580-8
Ziarek, Joshua J; Veldkamp, Christopher T; Zhang, Fuming et al. (2013) Heparin oligosaccharides inhibit chemokine (CXC motif) ligand 12 (CXCL12) cardioprotection by binding orthogonal to the dimerization interface, promoting oligomerization, and competing with the chemokine (CXC motif) receptor 4 (CXCR4) N terminus. J Biol Chem 288:737-46
Ducett, Jeanette K; Peterson, Francis C; Hoover, Lindsey A et al. (2013) Unfolding of the C-terminal domain of the J-protein Zuo1 releases autoinhibition and activates Pdr1-dependent transcription. J Mol Biol 425:19-31
Ziarek, Joshua J; Volkman, Brian F (2012) NMR in the Analysis of Functional Chemokine Interactions and Drug Discovery. Drug Discov Today Technol 9:e293-e299
DiCostanzo, Ara Celi; Thompson, James R; Peterson, Francis C et al. (2012) Tyrosine residues mediate fibril formation in a dynamic light chain dimer interface. J Biol Chem 287:27997-8006
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Tyler, Robert C; Murray, Nathan J; Peterson, Francis C et al. (2011) Native-state interconversion of a metamorphic protein requires global unfolding. Biochemistry 50:7077-9
Ziarek, Joshua J; Peterson, Francis C; Lytle, Betsy L et al. (2011) Binding site identification and structure determination of protein-ligand complexes by NMR a semiautomated approach. Methods Enzymol 493:241-75
Sun, Qingyu; Tyler, Robert C; Volkman, Brian F et al. (2011) Dynamic interchanging native states of lymphotactin examined by SNAPP-MS. J Am Soc Mass Spectrom 22:399-407

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