Comparison of the NMR and X‐ray structures of the HIV‐1 matrix protein: Evidence for conformational changes during viral assembly

Abstract

The three-dimensional solution-and solid-state structures of the human immunodeficiency virus type-1 (HIV-1) matrix protein have been determined recently in our laboratories by NMR and X-ray crystallographic methods (Massiah et al. 1994. J Mol Biol 244 : 198-223;Hill et al. 1996. Proc Natl Acad Sci USA 93:3099-3104). The matrix protein exists as a monomer in solution at low millimolar protein concentrations, but forms trimers in three different crystal lattices.Although the NMR and X-ray structures are similar, detailed comparisons have revealed an approximately 6 8, displacement of a short 3'0 helix (Pro 66-Gly 71) located at the trimer interface. High quality electron density and nuclear Overhauser effect (NOE) data support the integrity of the X-ray and NMR models, respectively. Because matrix apparently associates with the viral membrane as a trimer, displacement of the 310 helix may reflect a physiologically relevant conformational change that occurs during virion assembly and disassembly. These findings further suggest that Pro 66 and Gly 71, which bracket the 3'0 helix, serve as "hinges" that allow the 310 helix to undergo this structural reorientation.Keywords: human immunodeficiency virus type 1; matrix protein; NMR spectroscopy; retroviral assembly; X-ray crystallography The human immunodeficiency virus type-1 (HIV-I) genome encodes the structural Gag polyprotein (p55), which accumulates at the cell membrane during the late stages of the virus life cycle. Approximately 2,000 copies of the polyprotein assemble to form each immature virion. As these immature virions bud, the Gag polyproteins are cleaved by the viral protease into the three major viral structural proteins, matrix (MA, p17), capsid (CA, p24), and nucleocapsid (NC, p7), as well as three smaller peptide fragments (pl, p2, p6). These proteins subsequently undergo a major re- Abbreviations: HMQC-NOESY, heteronuclear multiple quantum coherence-nuclear Overhauser effect spectroscopy; NMR, nuclear magnetic resonance.arrangement, termed maturation, wherein the CA molecules condense to form the conical core particle that encapsidates the RNA-NC ribonucleoprotein complex, and the matrix proteins form a shell that remains associated with the inner face of the viral membrane (Gelderblom, 1991;Hoglund et al., 1992;Marx et al., 1988). Genetic analyses indicate that the matrix shell helps to anchor the transmembrane envelope protein (TM, gp41) on the surface of the virion, because mutations in both MA (Dorfman et al

Total chemical synthesis of N-myristoylated HIV-1 matrix protein p17: Structural and mechanistic implications of p17 myristoylation

“…Our finding indicates the existence of an energetically favorable interaction of a hydrophobic nature between the 14-carbon fatty acid moiety and proximal residues in the protein. The N terminus of p17 shown in various structural analyses is highly mobile (27)(28)(29), suggesting that it would not interfere with such an interaction. Whereas our data identify a ''myristoylhidden'' interaction mode for p17 in the absence of any spectroscopically discernible structural change in the protein, residues involved in the myristoyl sequestration remain to be structurally identified.…”

“…The question of how proteolytic processing of the Gag polyprotein during viral maturation induces a significant structural change in p17, and thus sequestration of the myristoyl moiety, remains unanswered. Although both NMR and crystal structures of recombinant nonmyristoylated p17 have been determined (25)(26)(27)(28)(29), these studies shed little light on the structural basis of the myristoyl switch hypothesis. Comparative studies of both myristoylated and nonmyristoylated p17 are needed to better understand the molecular mechanism by which it functions in the early and late stages of the HIV-1 life cycle.…”

Biochemical evidence of a role for matrix trimerization in HIV-1 envelope glycoprotein incorporation

“…Although NMR and crystal structures broadly agree on the structure of the MA monomer, these approaches differ in quaternary MA structure and at the trimer interface (30). Whereas NMR structures reveal only a monomer, crystallographic approaches reveal an MA trimer.…”

Molecular Interaction Studies of HIV-1 Matrix Protein p17 and Heparin

“…The structure of monomeric (33) and trimeric (34) p17 were determined, demonstrating highly similar three-dimensional structures (35). p17 folds into a compact core domain consisting of five ␣-helices and three stranded ␤-sheets.…”

“…Both of the motifs are not involved in mediating oligomerization of p17, remaining exposed onto the protein surface also when it takes its trimeric form (see also Fig. 1B) (34,35). Here, by integrating computational modeling, site directed mutagenesis of p17, chemical desulfation of heparin, and real time biomolecular interaction analysis by surface plasmon resonance (SPR), we characterized the interaction of p17 to heparin at a molecular level.…”