The large extracellular loop of CD63 interacts with gp41 of HIV-1 and is essential for establishing the virological synapse

Abstract

Human immunodeficiency virus type 1 (HIV-1) persists lifelong in infected individuals and has evolved unique strategies in order to evade the immune system. One of these strategies is the direct cell-to-cell spread of HIV-1. The formation of a virological synapse (VS) between donor and target cell is important for this process. Tetraspanins are cellular proteins that are actively involved in the formation of a VS. However, the molecular mechanisms of recruiting host proteins for the cell–cell transfer of particles to the VS remains unclear. Our study has mapped the binding site for the transmembrane envelope protein gp41 of HIV-1 within the large extracellular loop (LEL) of CD63 and showed that this interaction occurs predominantly at the VS between T cells where viral particles are transferred. Mutations within the highly conserved CCG motif of the tetraspanin superfamily abrogated recruiting of expressed HIV-1 GFP fused Gag core protein and CD63 to the VS. This demonstrates the biological significance of CD63 for enhanced formation of a VS. Since cell–cell spread of HIV-1 is a major route of persistent infection, these results highlight the central role of CD63 as a member of the tetraspanin superfamily during HIV-1 infection and pathogenesis.

Tetraspanins: Host Factors in Viral Infections

“…Tetraspanins CD63, CD81, and CD9 are recruited to virological synapses between T cells, and their depletion is associated with a drop in synapse formation [ 66 ]. More specifically, the large extracellular loop of CD63 was shown to interact with the HIV-1 gp41 protein [ 67 ]. This is postulated to prevent Env-mediated fusion between the donor and recipient cells, thus preventing syncytia formation [ 68 ].…”

Productive HIV-1 infection of tissue macrophages by fusion with infected CD4+ T cells

“…As tetraspanins are organized in membrane microdomains, CD81 could trap proteins involved in cell fusion, such as integrins among others ( Dufrancais et al, 2021 ; Hemler, 2005 ). The large extracellular loop of CD81 could also interact with gp41 exposed at the membrane of infected T cells, limiting the heterotypic cell fusion, as described for CD63 in the virological synapse ( Ivanusic et al, 2021 ; Kitadokoro et al, 2001 ). Moreover, our data disclose additional mechanism by which CD81 inhibits HIV-1-mediated heterotypic fusion through RhoA/ROCK activation and subsequent phosphorylation of myosin IIA, thus disturbing the macrophage actomyosin network unfavorable to fusion ( Fig.…”

Extracellular vesicles engineered to bind albumin demonstrate extended circulation time and lymph node accumulation in mouse models

“…The characterized structure of large extracellular loop (LEL, also the second loop) of CD81 was well defined (Charrin et al., 2009 ; Kitadokoro et al., 2001 ; Zimmerman et al., 2016 ), and the stabilization of the CD81 LEL by de novo disulphide bond was found to enhance its amenability for engineering into a more versatile protein scaffold (Vogt et al., 2018 ), which echoed our finding for ABD engineering. The LEL is larger than the first loop and is protruded from the membrane, allowing interaction with a variety of other protein partners (Ivanusic et al., 2021 ; Susa et al., 2020 ). The protrusion of LEL may allow engineering with different functional moieties, which is not delineated in our study, but is warranted for further investigation.…”