In a new study, researchers from Cornell University, the University of Virginia, the University of Delaware, the University of Missouri, the German European Molecular Biology Laboratory, and the Austrian Institute of Science and Technology provided new details of how the HIV-1 viral structure is assembled. This discovery provides a potential new target for the treatment of this viral infection. The relevant research results were published online in Nature.
This study reports that a small molecule called inositol hexakisphosphate (IP6) found in mammalian cells plays an important role in the immature development of this virus (occurring in infected cells) and maturation (occurs after the virus buds from the cell membrane and is cleaved from the cell).
Robert Dick, the first author of the paper and a postdoctoral researcher at Cornell University, said, “This small molecule plays a role in two different steps in the HIV-1 assembly pathway.” Dick is working in the lab of Volker Vogt, a senior author of the paper and a professor of molecular biology and genetics at Cornell University.
In the immature developmental and mature developmental stages of HIV-1, IP6 plays a key role in the pathways that form the protein lattice structure. When the virus develops within the cell, it helps to assemble the immature lattice. This immature crystal lattice undergoes degradation after germination of the virus and is cut from the cell membrane. During this time, IP6 also promotes the assembly of a mature protein lattice within this viral particle.
In this study, the researchers purified a structural protein called the Gag protein and mixed it with a nucleic acid that acts as a template, which forms a viral protein lattice type that is found during immature developmental stages. Dick and colleagues used a stain and electron microscope to observe the rounded virus particles on the grid (basically the viral protein lattice).
These researchers repeated the assembly reaction between Gag protein, nucleic acid, and buffer in the presence and absence of IP6. Dick said, “The first few experiments tell us that what we observed is very compelling. The presence of IP6 has greatly increased the number of virus particles we can detect.”
Nonetheless, these researchers are not sure where IP6 acts on the Gag protein to make an impact, so they construct different versions of the Gag protein and narrow the range of active sites to predict where IP6 molecules will play and to produce a lattice structure.
During this time, the researchers contacted Owen Pornillos and Barbie Ganser-Pornillos, researchers of the Department of Molecular Physiology and Biophysics at the University of Virginia, in which Pornillo and Ganser-Pornillos obtained crystallographic data when IP6 molecules interacted with Gag proteins.
During the mature developmental stage of the HIV-1 virus, these researchers found that IP6 interacts at sites which exposed after cleavage of the virus particles from the cells. During this time, a new lattice of different proteins (rather than an immature lattice) was produced.
These results find the way to the development of potential new therapies. One strategy is to develop or identify drugs that are similar to IP6 and bind to the same site as IP6, thereby blocking this small molecule and preventing the virus from maturing.
“One cell can produce millions of viral particles, but if these viral particles don’t go through this maturity, they are not contagious,” Dick said.
Robert A. Dick, Kaneil K. Zadrozny, Chaoyi Xu et al. Inositol phosphates are assembly co-factors for HIV-1. Nature, Published Online: 01 August 2018, doi:10.1038/s41586-018-0396-4.