Dynamic conformational switching in the chemokine ligand is essential for G Protein coupled-receptor activation

Chemokines mediate diverse functions from organogenesis to mobilizing leukocytes, and are unusual agonists for class-A GPCRs because of their large size and multi-domain structure. The current model for receptor activation, which involves interactions between chemokine N-loop and receptor N-terminal residues (Site-I) and between chemokine N-terminal and receptor extracellular loop/transmembrane residues (Site-II), fails to describe differences in ligand/receptor selectivity and the activation of multiple signaling pathways. Here, we show in neutrophil-activating chemokine CXCL8 that the highly conserved Gly-Pro (GP) motif located distal to both N-terminal and N-loop residues couples Site-I and Site-II interactions. Mutations in the GP motif showed large differences from native-like function to complete loss of activity that could not be correlated to the specific mutation, receptor affinity or subtype, or a specific signaling pathway. NMR studies indicated that the GP motif does not influence Site-I interactions, but molecular dynamics simulations suggested that this motif dictates substates of the CXCL8 conformational ensemble. We conclude that the GP motif enables diverse receptor functions by controlling crosstalk between Site-I and Site-II, and further propose that the repertoire of chemokine functions is best described by a conformational ensemble model in which a network of long-range coupled indirect interactions mediate receptor activity.

Source: BJ Signal - September 16, 2013 Category: Biochemistry Authors: P B. Joseph, K V. Sawant, A Isley, M Pedroza, R P. Garofalo, R M. Richardson, K Rajarathnam Tags: BJ Signal Source Type: research