The role of tyrosine sulfation in the dimerization of the CXCR4:SDF-1 complex.

Oligomerization of G protein-coupled receptors is a recognized mode of regulation of receptor activities, with alternate oligomeric states resulting in different signaling functions. The CXCR4 chemokine receptor is a G protein-coupled receptor that is post-translationally modified by tyrosine sulfation at three sites on its N-terminus (Y7, Y12, Y21), leading to enhanced affinity for its ligand, stromal cell derived factor (SDF-1, also called CXCL12). The complex has been implicated in cancer metastasis and is a therapeutic target in cancer treatment. Using molecular dynamics simulation of NMR-derived structures of the CXCR4 N-terminus in complex with SDF-1, and calculations of electrostatic binding energies for these complexes, we address the role of tyrosine sulfation in this complex. Our results show that sulfation stabilizes the dimeric state of the CXCR4:SDF-1 complex through hydrogen bonding across the dimer interface, conformational changes in residues at the dimer interface, and an enhancement in electrostatic binding energies associated with dimerization. These findings suggest a mechanism through which post-translational modifications such as tyrosine sulfation might regulate downstream function through modulation of the oligomeric state of the modified system.