Oligomerization-Enhanced Receptor-Ligand Binding Revealed by Dual-Color Simultaneous Tracking on Living Cell
Jiqiang Li1, Yanzhi Ding1, Hengheng Liu1
1State Key Laboratory of Heavy Oil Processing and Center for Bioengineering and Biotechnology, China University of Petroleum (East China), Qingdao 266580, P. R. China.
Abstract:
GPCR oligomerization plays a critical role in cellular signaling, yet the stoichiometry of the interactions between oligomers and binding ligands in living cells remains a longstanding challenge. Here, by developing a dual-color simultaneous tracking system based on a total internal reflection fluorescence microscope (TIRFM), the CCR5-CCL5 interactions are visualized and quantitatively assessed in real time. Results show that each oligomeric state of CCR5 could bind with CCL5 but with different binding affinities; CCR5 dimers have a 3.5-fold higher binding affinity than the monomers. The dimerization may cause an asymmetric conformational change which makes the first binding pocket have a 3.5-fold higher binding affinity and the second have only a half compared with the monomeric CCR5. This study is the first example to directly scrutinize the CCR5-CCL5 interactions at the single-molecule level on living cell membranes and will offer great potential for the interaction stoichiometry study of diverse surface proteins.
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