The interaction of CC chemokine binding protein vCCI with CCL17(TARC).

Abstract

Inflammation is associated with pathologies such as allergic asthma and atopic dermatitis, and occurs when chemokines are secreted at a site of injury or infection. Chemokines are small proteins that bind cognate receptors on leukocytes and mediate activation and chemotaxis to the site of inflammation. As such, inhibiting chemokines in some cases could be an appealing target to control inflammation. Many viruses have evolved strategies to subvert the human chemokine system by producing chemokine binding proteins. Among them, poxviruses encode vCCI (viral CC chemokine inhibitor), which has been shown to bind about 20 different CC chemokines with high affinity (nanomolar or sub-nanomolar). However, there is at least one CC chemokine that has been qualitatively shown to bind poorly to vCCI, namely TARC (also called CCL17). CCL17/TARC is secreted by dendritic cells and endothelial cells, among others. It has been known to bind tightly to its receptor CCR4, which is associated with type 2 immune responses. TARC, however, unlike almost every other chemokine in its subfamily, apparently does not bind vCCI well. To identify the amino acids mediating TARC-vCCI binding, we performed molecular dynamic simulations of TARC in complex with vCCI. We then designed several mutations to TARC that our simulations suggested would lead to increased binding to vCCI, including G17R, V44K, Q45R and R57W. We used Biolayer Interferometry (BLI) to determine that some of these variants showed increased binding ability. We will report the results of a combination of BLI, NMR, and fluorescence studies of TARC binding to vCCI. Successfully understanding the key residues involved in the interaction between TARC and vCCI would pave a way for vCCI as a therapeutic candidate for TARC-related inflammation treatment and diagnosis.