HIV-1 Nef membrane association depends on charge, curvature, composition and sequence

Abstract

Nef-mediated internalization of T-cell receptor molecules from the surface of an infected cell is required for the pathogenicity of HIV and disease progression to AIDS. This function depends on the N-terminal myristoylation of Nef, a lipid modification that targets the protein to membranes. We have analyzed how specific membrane properties and sequence motifs within Nef determine this interaction. Using time-resolved techniques we find that the association with membranes is a biphasic process with a fast rate for an electrostatic-driven protein-liposome interaction and a slow rate for the formation of an amphipathic helix. The rate of myristate insertion into liposomes depends on membrane curvature, while changes in the lipid composition with respect to phosphoinositides, cholesterol or sphingomyelin did not significantly alter the interaction. Moreover, Nef binding to membranes requires negatively charged liposomes, and mutations of basic and hydrophobic residues strongly diminished the association and changed the binding kinetics differently.

HIV-1 Nef mobilizes lipid rafts in macrophages through a pathway that competes with ABCA1-dependent cholesterol efflux

“…Nef induces a number of genes involved in cholesterol synthesis ( 8,9 ) and can facilitate cholesterol delivery to lipid rafts ( 8,10 ). This activity is consistent with membrane localization of Nef due to myristoylation ( 8,11,12 ); nonmyristoylated Nef did not affect lipid rafts ( 8 ). Lipid rafts are the preferential sites of HIV-1 assembly and budding, and cholesterol content of lipid rafts determines the cholesterol content of virions, which is critical for virion infectivity.…”

A C-terminal Membrane Anchor Affects the Interactions of Prion Proteins with Lipid Membranes

“…In general this effect does not depend on the presence or absence of a membrane anchor, as a similar effect was found for all PrP variants in interactions with POPG liposomes. Based on this observation a direct interaction of the PrP N-terminal region with phospholipid membranes always occurs, as described for other lipid-anchored proteins such as Src proteins and HIV-1 Gag protein (27,44). However, tryptophan fluorescence quenching occurred to a different extent for PrPs with a membrane anchor compared with PrPs without a membrane anchor.…”

The Protein Lipidation and Its Analysis

“…This is the case of the HIV viral protein Gag, whose myristoylation is critical for the formation of the viral capsid [39]. Similarly, the Nef protein, essential for viral replication, high virus load and progression to acquired immunodeficiency syndrome (AIDS), requires membrane association via myristoylation to exert its functions [40]. This together with the fact that myristoylation is misregulated in many other diseases (cancer, [41] neurological disorders [42]) has supported NMT as a potential therapeutical target.…”