The Novel Purification and Biophysical Characterization of CXC Chemokines

Abstract

The chemokines are small, signaling proteins responsible for leukocyte recruitment through concentration gradient driven responses for inflammatory diseases such as tissue damage or sun burn, tumor suppression and regulation, and obesity from insulin resistance. In particular, the CXC family of chemokines are active as monomers, homodimers, and heterodimers, with binding affinities for multiple CXC G-protein-coupled receptors. This intricate network has been linked to many cell signaling pathways, but the overall protein folding mechanisms as a concentration driven monomer-dimer equilibrium have yet to be established. In this work, a novel, inclusion body purification is developed to express and purify biologically active CXCL chemokines in milligram quantities for thermodynamic and kinetic biophysical characterization experiments. The results show, that the CXCL chemokines folds and self-associates into homodimers that can activate a membrane bound CXC Receptor, at concentrations above 20 M. Interestingly, the tested CXC ligands display different native circular dichroism spectrum and have stability DG values from 5 to 20 kcal/mol. This indicates the chemokine network has evolved both its specificity and promiscuity to finetune the delicate interplay between ligands and receptors. Thus, these initial studies of the CXC chemokines establishes the foundation for further characterization of chemokines to define fundamental principles governing protein-protein interaction. These principles will help to elucidate molecular details of chemokine-signaling with a long-term goal of finding new drug targets to enhance or suppress signaling.