Medical College of Wisconsin
CTSICores SearchResearch InformaticsREDCap

The CXC chemokine receptor 4 ligands ubiquitin and stromal cell-derived factor-1α function through distinct receptor interactions. J Biol Chem 2011 Sep 23;286(38):33466-77



Pubmed ID


Pubmed Central ID




Scopus ID

2-s2.0-80052987287   69 Citations


Recently, we identified extracellular ubiquitin as an endogenous CXC chemokine receptor (CXCR) 4 agonist. However, the receptor selectivity and molecular basis of the CXCR4 agonist activity of ubiquitin are unknown, and functional consequences of CXCR4 activation with ubiquitin are poorly defined. Here, we provide evidence that ubiquitin and the cognate CXCR4 ligand stromal cell-derived factor (SDF)-1α do not share CXCR7 as a receptor. We further demonstrate that ubiquitin does not utilize the typical two-site binding mechanism of chemokine-receptor interactions, in which the receptor N terminus is important for ligand binding. CXCR4 activation with ubiquitin and SDF-1α lead to similar Gα(i)-responses and to a comparable magnitude of phosphorylation of ERK-1/2, p90 ribosomal S6 kinase-l and Akt, although phosphorylations occur more transiently after activation with ubiquitin. Despite the similarity of signal transduction events after activation of CXCR4 with both ligands, ubiquitin possesses weaker chemotactic activity than SDF-lα in cell migration assays and does not interfere with productive entry of HIV-1 into P4.R5 multinuclear activation of galactosidase indicator cells. Unlike SDF-1α, ubiquitin lacks interactions with an N-terminal CXCR4 peptide in NMR spectroscopy experiments. Binding and signaling studies in the presence of antibodies against the N terminus and extracellular loops 2/3 of CXCR4 confirm that the ubiquitin CXCR4 interaction is independent of the N-terminal receptor domain, whereas blockade of extracellular loops 2/3 prevents receptor binding and activation. Our findings define ubiquitin as a CXCR4 agonist, which does not interfere with productive cellular entry of HIV-1, and provide new mechanistic insights into interactions between CXCR4 and its natural ligands.

Author List

Saini V, Staren DM, Ziarek JJ, Nashaat ZN, Campbell EM, Volkman BF, Marchese A, Majetschak M


Adriano Marchese PhD Professor in the Biochemistry department at Medical College of Wisconsin
Brian F. Volkman PhD Professor in the Biochemistry department at Medical College of Wisconsin

MESH terms used to index this publication - Major topics in bold

Cell Line
Chemokine CXCL12
HIV Infections
Mitogen-Activated Protein Kinases
Protein Binding
Protein Structure, Tertiary
Receptors, CXCR4