 The bundle allows the viral and cellular membranes to approximate and eventually fuse together, leading to the release of the viral genome into the cytoplasm of the target cell.The two coreceptors involved in the entry of HIV-1, CCR5 and CXCR4, belong to the larger family of 7-transmembrane segment (7TM) G-protein coupled receptors.HIV-1 can thus be classified according to specificity for one coreceptor or the other.