Structural insights into Immune Signaling through the CXCR4:MIF Molecular Complex Engineered for Solubility

The interactions between chemokine ligands and their receptors mediates the ability of the immune system to protect against threats to homeostasis. Signaling through the human macrophage migration inhibitory factor – chemokine receptor 4 (hMIF-CXCR4) signaling axis is crucial for protection from cancer metastasis and sepsis through the regulation of cell migration and proliferation. An understanding of the consequences of signaling through the hMIF-CXCR4 axis opens the door to the development of therapies against sepsis and cancer metastasis, both of which currently have no cure and have limited treatment options. However, hMIF and CXCR4 are highly promiscuous, which makes the development of targeted therapies difficult due to the prevalence of off-target affects. Developing targeted therapies that specifically modulate the interaction between hMIF and CXCR4 without affecting their interactions with other binding partners therefore necessitates a detailed structural understanding of the interaction. Unfortunately, the field currently lacks structural information revealing the interaction between hMIF and CXCR4 due to technical limitations in studying the interactions between soluble and membrane embedded proteins. This study seeks to circumvent these technical limitations by using an aqueous soluble mutant of CXCR4, CXCR4^QTY, that retains its structural integrity and ligand binding ability outside membrane and in detergent-free buffer. Utilizing CXCR4^QTY, atomic level details of the interaction between hMIF and CXCR4 are investigated, facilitating the development of targeted therapies that specifically modulate their interaction without off target affects.