Identification of a Salt Bridge That Is Functionally Important for Chemokine Receptor CXCR1 but not CXCR2

CXC chemokine receptors 1 (CXCR1) and 2 (CXCR2) havehigh sequencesimilarity and overlapping chemokine ligand profiles. Residue positions3.32 and 7.39 are critical for signal transduction in the relatedCXCR4, and in these positions CXCR1 and CXCR2 contain oppositely chargedresidues (Lys(3.32) and Glu(7.39)). Experimentaland computed receptor structures reveal the possible formation ofa salt bridge between transmembrane (TM) helices 3 and 7 via thesetwo residues. To investigate the functional importance of Lys117(3.32) and Glu291(7.39) in CXCR1, along with the flankingGlu118(3.33), we performed a signaling study on 16 CXCR1mutants using two different CXCL8 isoforms. While single Ala-mutation(K117(3.32)A, E291(7.39)A) and charge reversal (K117(3.32)E, E291(7.39)K) resulted in nonfunctional receptors,double (K117(3.32)E-E291(7.39)K) and triple (K117(3.32)E-E118(3.33)A-E291(7.39)K) mutants rescuedCXCR1 function. In contrast, the corresponding mutations did not affectthe CXCR2 function to the same extent. Our findings show that theLys(3.32)-Glu(7.39) salt bridge between TM3 and-7 is functionally important for CXCR1 but not for CXCR2, meaningthat signal transduction for these highly homologous receptors isnot conserved.

Automated summary

Research has shown that residue positions 3.32 and 7.39 play a critical role in signal transduction of CXCR1, but have less effect on CXCR2. These positions form a salt bridge between TM helices 3 and 7, which is important for CXCR1 function.