Highly Sensitive Analysis of the Interaction between HIV-1 Gag and Phosphoinositide Derivatives Based on Surface Plasmon Resonance

HIV-1 Gag, which drives virion assembly, interacts with a plasma membrane (PM)-specific phosphoinositide, phosphatidylinositol-(4,5)-bisphosphate [PI(4,5)P 2 ]. While cellular acidic phospholipid-binding proteins/domains, such as the PI(4,5)P 2 -specific pleckstrin homology domain of phospholipase C␦1 (PH PLC␦1 ), mediate headgroup-specific interactions with corresponding phospholipids, the exact nature of the Gag-PI(4,5)P 2 interaction remains undetermined. In this study, we used giant unilamellar vesicles (GUVs) to examine how PI(4,5)P 2 with unsaturated or saturated acyl chains affect membrane binding of PH PLC␦ 1 and Gag. Both unsaturated dioleoyl-PI(4,5)P 2 [DO-PI(4,5)P 2 ] and saturated dipalmitoyl-PI(4,5)P 2 [DP-PI(4,5)P 2 ] successfully recruited PH PLC␦ 1 to membranes of single-phase GUVs. In contrast, DO-PI(4,5)P 2 but not DP-PI(4,5)P 2 recruited Gag to GUVs, indicating that PI(4,5)P 2 acyl chains contribute to stable membrane binding of Gag. GUVs containing PI(4,5)P 2 , cholesterol, and dipalmitoyl phosphatidylserine separated into two coexisting phases: one was a liquid phase, and the other appeared to be a phosphatidylserine-enriched gel phase. In these vesicles, the liquid phase recruited PH PLC␦ 1 regardless of PI(4,5)P 2 acyl chains. Likewise, Gag bound to the liquid phase when PI(4,5)P 2 had DO-acyl chains. DP-PI(4,5)P 2 -containing GUVs showed no detectable Gag binding to the liquid phase. Unexpectedly, however, DP-PI(4,5)P 2 still promoted recruitment of Gag, but not PH PLC␦ 1 , to the dipalmitoyl-phosphatidylserine-enriched gel phase of these GUVs. Altogether, these results revealed different roles for PI(4,5)P 2 acyl chains in membrane binding of two PI(4,5)P 2 -binding proteins, Gag and PH PLC␦ 1 . Notably, we observed that nonmyristylated Gag retains the preference for PI(4,5)P 2 containing an unsaturated acyl chain over DP-PI(4,5)P 2 , suggesting that Gag sensitivity to PI(4,5)P 2 acyl chain saturation is determined directly by the matrix-PI(4,5)P 2 interaction, rather than indirectly by a myristate-dependent mechanism. IMPORTANCEBinding of HIV-1 Gag to the plasma membrane is promoted by its interaction with a plasma membrane-localized phospholipid, PI(4,5)P 2 . Many cellular proteins are also recruited to the plasma membrane via PI(4,5)P 2 -interacting domains represented by PH PLC␦ 1 . However, differences and/or similarities between these host proteins and viral Gag protein in the nature of their PI(4,5)P 2 interactions, especially in the context of membrane binding, remain to be determined. Using a novel giant unilamellar vesicle-based system, we found that PI(4,5)P 2 with an unsaturated acyl chain recruited PH PLC␦ 1 and Gag similarly, whereas PI(4,5)P 2 with saturated acyl chains either recruited PH PLC␦ 1 but not Gag or sorted these proteins to different phases of vesicles. To our knowledge, this is the first study to show that PI(4,5)P 2 acyl chains differentially modulate membrane binding of PI(4,5)P 2 -binding proteins. Since Gag membrane binding is essential for progeny...

Section: Discussionmentioning

confidence: 98%

mentioning

confidence: 96%

Phosphatidylinositol-(4,5)-Bisphosphate Acyl Chains Differentiate Membrane Binding of HIV-1 Gag from That of the Phospholipase Cδ1 Pleckstrin Homology Domain

Olety

Veatch

Ono

2015

“…Although the interaction between MA and PI(4,5)P 2 has already been investigated by a variety of biophysical techniques (26,58,63,64), quantitative binding data of the protein to this lipid in the context of bilayer membranes are still scarce (65) and data measured out of the membrane context tend to underestimate affinities. For example, solution NMR studies reported a dissociation constant (K d ) of Ϸ150 M for myristoylated HIV-1 MA with soluble di-C 4 -PI(4,5)P 2 and a slightly higher affinity to di-C 8 -PI(4,5)P 2 (26).…”

Section: Discussionmentioning

confidence: 99%

Membrane Binding of HIV-1 Matrix Protein: Dependence on Bilayer Composition and Protein Lipidation

Barros

Heinrich

Datta

et al. 2016

By assembling in a protein lattice on the host's plasma membrane, the retroviral Gag polyprotein triggers formation of the viral protein/membrane shell. The MA domain of Gag employs multiple signals-electrostatic, hydrophobic, and lipid-specific-to bring the protein to the plasma membrane, thereby complementing protein-protein interactions, located in full-length Gag, in lattice formation. We report the interaction of myristoylated and unmyristoylated HIV-1 Gag MA domains with bilayers composed of purified lipid components to dissect these complex membrane signals and quantify their contributions to the overall interaction. Surface plasmon resonance on well-defined planar membrane models is used to quantify binding affinities and amounts of protein and yields free binding energy contributions, ⌬G, of the various signals. Charge-charge interactions in the absence of the phosphatidylinositide PI(4,5)P 2 attract the protein to acidic membrane surfaces, and myristoylation increases the affinity by a factor of 10; thus, our data do not provide evidence for a PI(4,5)P 2 trigger of myristate exposure. Lipid-specific interactions with PI(4,5)P 2 , the major signal lipid in the inner plasma membrane, increase membrane attraction at a level similar to that of protein lipidation. While cholesterol does not directly engage in interactions, it augments protein affinity strongly by facilitating efficient myristate insertion and PI(4,5)P 2 binding. We thus observe that the isolated MA protein, in the absence of protein-protein interaction conferred by the full-length Gag, binds the membrane with submicromolar affinities. IMPORTANCELike other retroviral species, the Gag polyprotein of HIV-1 contains three major domains: the N-terminal, myristoylated MA domain that targets the protein to the plasma membrane of the host; a central capsid-forming domain; and the C-terminal, genome-binding nucleocapsid domain. These domains act in concert to condense Gag into a membrane-bounded protein lattice that recruits genomic RNA into the virus and forms the shell of a budding immature viral capsid. In binding studies of HIV-1 Gag MA to model membranes with well-controlled lipid composition, we dissect the multiple interactions of the MA domain with its target membrane. This results in a detailed understanding of the thermodynamic aspects that determine membrane association, preferential lipid recruitment to the viral shell, and those aspects of Gag assembly into the membrane-bound protein lattice that are determined by MA. T he polyprotein Gag is an essential component for the reproduction of retroviruses, such as HIV-1, in infected cells. In the production of new viruses, many copies of Gag assemble laterally, either in the cytoplasm or on the plasma membrane (PM) of the host, thus acquiring their lipid envelope as they bud from the cell. Distinct retroviral genera encode Gag proteins which all show a similar domain architecture, with an N-terminal matrix (MA) domain that targets the PM, followed by the capsid (CA) and nucleocapsid ...

“…NMR, surface plasmon resonance, and protein footprinting studies of HIV-1 MA/ Gag-PI(4,5)P 2 complexes revealed that the basic residues in HBR associate with water-soluble derivatives of PI(4,5)P 2 (4,61,62). Interaction of HIV-1 Gag and MA with membrane-associated PI(4,5)P 2 in its natural cellular form was demonstrated using liposomes or a lipid monolayer system (3,13,14).…”

mentioning

confidence: 99%

Assembly and Replication of HIV-1 in T Cells with Low Levels of Phosphatidylinositol-(4,5)-Bisphosphate

Monde

Chukkapalli

Ono

2011

HIV-1 Gag assembles into virus particles predominantly at the plasma membrane (PM). Previously, we observed that phosphatidylinositol-(4,5)-bisphosphate [PI(4,5)P 2 ] is essential for Gag binding to the plasma membrane and virus release in HeLa cells. In the current study, we found that PI(4,5)P 2 also facilitates Gag binding to the PM and efficient virus release in T cells. Notably, serial passage of HIV-1 in an A3.01 clone that expresses polyphosphoinositide 5-phosphatase IV (5ptaseIV), which depletes cellular PI(4,5)P 2 , yielded an adapted mutant with a Leu-to-Arg change at matrix residue 74 (74LR). Virus replication in T cells expressing 5ptaseIV was accelerated by the 74LR mutation relative to replication of wild type HIV-1 (WT). This accelerated replication of the 74LR mutant was not due to improved virus release. In control T cells, the 74LR mutant releases virus less efficiently than does the WT, whereas in cells expressing 5ptaseIV, the WT and the 74LR mutant are similarly inefficient in virus release. Unexpectedly, we found that the 74LR mutation increased virus infectivity and compensated for the inefficient virus release. Altogether, these results indicate that PI(4,5)P 2 is essential for Gag-membrane binding, targeting of Gag to the PM, and efficient virus release in T cells, which in turn likely promotes efficient virus spread in T cell cultures. In T cells with low PI(4,5)P 2 levels, however, the reduced virus particle production can be compensated for by a mutation that enhances virus infectivity.