Effects of an HIV-1 maturation inhibitor on the structure and dynamics of CA-SP1 junction helices in virus-like particles

Abstract

HIV-1 maturation involves conversion of the immature Gag polyprotein lattice, which lines the inner surface of the viral membrane, to the mature capsid protein (CA) lattice, which encloses the viral RNA. Maturation inhibitors such as bevirimat (BVM) bind within six-helix bundles, formed by a segment that spans the junction between the CA and spacer peptide 1 (SP1) subunits of Gag, and interfere with cleavage between CA and SP1 catalyzed by the HIV-1 protease (PR). We report solid-state NMR (ssNMR) measurements on spherical virus-like particles (VLPs), facilitated by segmental isotopic labeling, that provide information about effects of BVM on the structure and dynamics of CA–SP1 junction helices in the immature lattice. Although BVM strongly blocks PR-catalyzed CA–SP1 cleavage in VLPs and blocks conversion of VLPs to tubular CA assemblies, 15N and 13C ssNMR chemical shifts of segmentally labeled VLPs with and without BVM are very similar, indicating that interaction with BVM does not alter the six-helix bundle structure appreciably. Only the 15N chemical shift of A280 (the first residue of SP1) changes significantly, consistent with BVM binding to an internal ring of hydrophobic side chains of L279 residues. Measurements of transverse 15N spin relaxation rates reveal a reduction in the amplitudes and/or timescales of backbone N–H bond motions, corresponding to a rigidification of the six-helix bundles. Overall, our data show that inhibition of HIV-1 maturation by BVM involves changes in structure and dynamics that are surprisingly subtle, but still sufficient to produce a large effect on CA–SP1 cleavage.

Physics of viral dynamics

“…Maturation is promoted and inhibited in various processes. Structural and dynamic studies using solution nuclear magnetic resonance (NMR) and solid-state NMR have shed light on proteolytic processing of Gag 97 and the effect of maturation inhibitors 98 . Furthermore, cryo-electron tomography that included subtomogram averaging 99 was used to study Gag regions that are targeted by maturation inhibitors 100 .…”

The HIV-1 maturation inhibitor, EP39, interferes with the dynamic helix-coil equilibrium of the CA-SP1 junction of Gag

“…In the latest published article about the effect of BVM on the structure and dynamics of CA-SP1 junction, the assigned signals of SP1 ends at SP1-A 232 (A282 in their numbering scheme) due to the high dynamics of SP1. Their data show that BVM causes subtle changes in the structure and dynamics of CASP1 junction [20]. However, the lost of information in the SP1 domain makes it impossible to clarify the essential role of SP1-QVT motif in the binding of the maturation inhibitor.…”

HIV-1 Maturation: Lessons Learned from Inhibitors

“…Although work over the past several years has greatly increased our understanding of MI activity, several important questions remain. A recent NMR study demonstrated that BVM-induced changes in the structure and dynamics of the six-helix bundle of spherical virus-like particles (VLPs) were surprisingly subtle, raising questions about the mechanism by which MIs stabilize this region [ 83 ]. The dynamic nature of the CA-SP1 boundary continues to present challenges for defining the atomic-level structure of this region.…”