Chemokines are a family of pro-inflammatory proteins that interact with G-protein-coupled receptors. Structurally, chemokines are categorized into 4 major subfamilies (C, CC, CXC, and CX3C), which are distinguished by the presence of cysteines near the N terminus of the protein. Among these subfamilies of chemokines exists XCL1 (lymphotactin), a member of the C-class chemokine family, which is classified by its unique disulfide bonding pattern and receptor activity. XCL1 is also unique among chemokines for its ability to interconvert between two alternate structures, where one of the structures adheres to the standard chemokine fold and the other is an all-beta sheet with glycosaminoglycan binding ability. The activities of the pro-inflammatory chemokines can be inhibited by the presence of a viral CC chemokine inhibitor (vCCI) produced by poxviruses. Previous experiments have shown that vCCI has a high binding affinity (at nanomolar levels) to members of the CC-chemokine subfamily; however, vCCI lacks the ability to tightly bind to other subfamilies of the chemokine protein, despite these subfamilies sharing the same general fold. Here, we describe a study that focuses on a C subfamily—XCL1—where mutations are introduced to key positions in the chemokine to promote a stronger binding of XCL1 to vCCI. We employed molecular dynamics simulations in conjunction with experimental techniques, such as bio-layer interferometry, to investigate which mutations would lead to a tighter binding within the complex. This work will elucidate important protein-protein interactions in the vCCI:XCL1 complex and may lead to strategies for the specific inhibition of particular chemokines relevant to disease.
Oluebube C. Onwuzulu (Sun,) studied this question.