Viral GPCR US28 can signal in response to chemokine agonists of nearly unlimited structural degeneracy

Elife. 2018 Jun 8;7:e35850. doi: 10.7554/eLife.35850.

Abstract

Human cytomegalovirus has hijacked and evolved a human G-protein-coupled receptor into US28, which functions as a promiscuous chemokine 'sink' to facilitate evasion of host immune responses. To probe the molecular basis of US28's unique ligand cross-reactivity, we deep-sequenced CX3CL1 chemokine libraries selected on 'molecular casts' of the US28 active-state and find that US28 can engage thousands of distinct chemokine sequences, many of which elicit diverse signaling outcomes. The structure of a G-protein-biased CX3CL1-variant in complex with US28 revealed an entirely unique chemokine amino terminal peptide conformation and remodeled constellation of receptor-ligand interactions. Receptor signaling, however, is remarkably robust to mutational disruption of these interactions. Thus, US28 accommodates and functionally discriminates amongst highly degenerate chemokine sequences by sensing the steric bulk of the ligands, which distort both receptor extracellular loops and the walls of the ligand binding pocket to varying degrees, rather than requiring sequence-specific bonding chemistries for recognition and signaling.

Keywords: E. coli; G protein-coupled receptor; S. cerevisiae; biased signaling; biochemistry; chemical biology; chemokine; human; membrane protein crystallography; molecular biophysics; structural biology; yeast surface display.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Chemokine CX3CL1 / chemistry*
  • Chemokine CX3CL1 / metabolism
  • Chemokine CX3CL1 / pharmacology
  • Cytomegalovirus / genetics
  • Cytomegalovirus / metabolism
  • GTP-Binding Proteins / chemistry
  • GTP-Binding Proteins / genetics
  • GTP-Binding Proteins / metabolism
  • HEK293 Cells
  • High-Throughput Nucleotide Sequencing
  • Humans
  • Ligands
  • Models, Molecular
  • Mutation
  • Protein Binding
  • Protein Conformation
  • Receptors, Chemokine / agonists
  • Receptors, Chemokine / chemistry*
  • Receptors, Chemokine / metabolism
  • Receptors, G-Protein-Coupled / agonists
  • Receptors, G-Protein-Coupled / chemistry*
  • Receptors, G-Protein-Coupled / metabolism
  • Signal Transduction*
  • Viral Proteins / agonists
  • Viral Proteins / chemistry*
  • Viral Proteins / metabolism

Substances

  • Chemokine CX3CL1
  • Ligands
  • Receptors, Chemokine
  • Receptors, G-Protein-Coupled
  • US28 receptor, Cytomegalovirus
  • Viral Proteins
  • GTP-Binding Proteins