Structural basis of CXCR4 assembly and regulation.

CXC chemokine receptor 4 (CXCR4) is a well-established drug target and a key representative of the chemokine receptor family. Chemokine receptors tend to assemble, and this assembly plays a critical role in regulating their functions. However, structural information regarding the organization of these receptors remains limited. Here, we present the cryoelectron microscopy (cryo-EM) structure of a CXCR4 homo-tetramer. In this tetramer, each protomer interfaces with adjacent protomers via TM1/2 and TM5/6/7, aligning at a 90° angle to assemble into a C4 rotationally symmetric arrangement. Each protomer allosterically regulates the others, with Q272 in the ECL3 loop interacting with K38 (TM1) and V99 (TM2) of the adjacent protomer, resulting in a mutually inhibitory configuration. These findings reveal an allosteric and antagonistic mechanism that prevents excessive activation, providing a structural framework for understanding the molecular mechanisms driving CXCR4 self-assembly and offering insights that could inspire further therapeutic strategies.