Human chemokine receptors CCR5, CCR3 and CCR2B share common polarity motifin the first extracellular loop with other human G-protein coupled receptors - Implications for HIV-1 coreceptor function

Chemokine receptors (CRs) are 7-helix membrane proteins from the family of G-protein coupled receptors (GPCRs). A few human CRs act as cofactors for m acrophage-tropic (M-tropic) human immunodeficiency virus type-1 (HIV-1) ent ry into cells, while others do not. In this study, we describe an applicati on of molecular modeling techniques to delineate common molecular determina nts that might be related to coreceptor activity and the use of the data to identify other GPCRs as putative cofactors for M-tropic HIV-1 entry. Subse quently, the results were confirmed by an experimental approach. The sequen ces of extracellular domains (ECDs) of CRs were employed in a compatibility search against a database of environmental profiles derived for proteins w ith known spatial structure. The best-scoring sequence-profile alignments o btained for each ECD were compared in pairs to check for common patterns in residue environments, and consensus sequence-profile fits for ECDs were al so derived. Similar hydrophobicity motifs were found in the first extracell ular loops of the CRs CCR5, CCR3, and CCR2B, and are all used by M-tropic H IV-1 for cell entry. In contrast, other CRs did not reveal common motifs. H owever, the same environmental pattern was also delineated in the first ext racellular loop of some human GPCRs showing either high (group 1) or low (g roup 2) degree of similarity of their polarity patterns with those in HIV-1 coreceptors. To address the question of whether the delineated molecular d eterminant plays a critical role in the receptor-virus binding, three of th e identified GPCRs, bradykinin receptor (BRB2) and G-protein receptor (GPR) -CY6 from group 1, and GPR8 from group 2, were cloned and transfected into HeLa-CD4 cells, which are nonpermissive to M-tropic HIV-1 infection. We dem onstrate that, similar to CCR5, the two selected GPCRs from group 1 were ca pable of mediating M-tropic HIV-1 entry, whereas GPR8 from group 2 did not serve as HIV-1 coreceptor. The potential biological significance of the ide ntified structural motif shared by the human CCR5, CCR3, CCR2B and other GP CRs is discussed.