HIV Entry: Receptors Cooperate with Membrane Domain Boundaries to form Entry Sites in Host Cells

Abstract

It has been proposed that lipid rafts of host cell membranes play pivotal roles for cell entry of many enveloped viruses including HIV. However, it remains largely unknown why virions would prefer nanoscopic ordered lipid domains over uniformly fluid membrane regions. Here, we show that HIV does not enter cells from within ordered membrane regions, but rather at the boundaries between raft-like and non-raft-like regions of the plasma membrane. Using cell-derived giant plasma membrane vesicles (GPMVs), which are phase-separated into large-scale liquid-ordered (Lo) and liquid-disordered (Ld) membrane domains, we demonstrate that the HIV receptor CD4 is substantially sequestered into Lo domains while the coreceptor CCR5 localizes preferentially at Lo/Ld domain boundaries. Lo/Ld phase coexistence is not required for HIV attachment, but the recognition of Lo/Ld boundaries is a prerequisite for successful fusion of the viral envelope with the cell membrane. We propose that virions localized to membrane domain boundaries utilize their interfacial energy as an additional driving force for fusion and cell entry. This study provides surprising answers to the long-standing question about the roles of lipid rafts in cell entry of HIV and perhaps other enveloped viruses.