Role for Gag-CA Interdomain Linker in Primate Lentiviral Replication

Abstract

Gag proteins underlie retroviral replication by fulfilling numerous functional roles at various stages during viral life cycle. Out of the four mature proteins, Gag-capsid (CA) is a major component of viral particles, and has been most well studied biogenetically, biochemically and structurally. Gag-CA is composed of two structured domains, and also of a short stretch of disordered and flexible interdomain linker. While the two domains, namely, N-terminal and C-terminal domains (NTD and CTD), have been the central target for Gag research, the linker region connecting the two has been poorly studied. We recently have performed systemic mutational analyses on the Gag-CA linker region of HIV-1 by various experimental and in silico systems. In total, we have demonstrated that the linker region acts as a cis -modulator to optimize the Gag-related viral replication process. We also have noted, during the course of conducting the research project, that HIV-1 and SIVmac, belonging to distinct primate lentiviral lineages, share a similarly biologically active linker region with each other. In this brief article, we summarize and report the results obtained by mutational studies that are relevant to the functional significance of the interdomain linker of HIV/SIV Gag-CA. Based on this investigation, we discuss about the future directions of the research in this line.

Mutation in the Disordered Linker Region of Capsid Disrupts Viral Kinetics of a Neuropathogenic SIV in Rhesus Macaques

“…It has been previously demonstrated that HIV Pro-147 is part of a disordered linker domain which connects the HIV capsid N-terminal domain (CA-NTD) and the capsid C-terminal domain (CA-CTD) ( 26 , 27 ). Mutations in this domain can result in improper formation of the capsid, leading to a reduction in the number of viable virions produced, and SIV shares a similarly biologically active linker region with HIV ( 28 ). The presence of Thr-146 is presumably an error that arose during PCR and cloning, since bulk sequence analysis of the virus isolate that was the source of the CL757 cloned, SIVsmm804E ( 12 ), showed that this isolate and additional clones from it encoded a Pro at this site (data not shown).…”

Human Immunodeficiency Virus Type 2 Capsid Protein Mutagenesis Reveals Amino Acid Residues Important for Virus Particle Assembly

“…Mutagenesis studies have been used to confirm the importance of the interface residues for core morphology and stability and virion infectivity (24,25,30,31). Mutations in the CA domain of Gag have been shown to affect particle assembly and virion infectivity in different retroviruses, including HIV-1 (32), Simian immunodeficiency virus (SIV) (33), Mason-Pfizer monkey virus (M-PMV) (34), and RSV (35).…”

Human immunodeficiency virus type 2 capsid protein mutagenesis reveals amino acid residues important for virus particle assembly

“…Several key mutants, such as HIV-1 CA W184A and M185A caused Gag assembly defects, produced non-infectious viruses, reduced CA dimerization and intermolecular Gag–Gag interactions in vitro , diminished immature particle production in vivo , and abolished CA dimerization [29, 35]. Moreover, parallel studies have been done on SIVmac constructs [32]. However, there have been no studies focused on HIV-2 critical amino acids.…”

“…Mutagenesis studies have been used to confirm the importance of the interface residues for core morphology and stability and virion infectivity (24, 25, 30, 31). Mutations in the CA domain of Gag have been shown to affect particle assembly and virion infectivity in different retroviruses, including HIV-1 (32), Simian immunodeficiency virus (SIV) (33), Mason-Pfizer monkey virus (M-PMV) (34), and RSV (35). Several key mutants, for example the HIV-1 CA W184A and M185A cause Gag assembly defects, produce non-infectious virus particles, reduce CA dimerization and intermolecular Gag–Gag interactions in vitro , diminish immature particle production in vivo , and abolish CA dimerization (30, 36); similar studies have been done with SIV (33).…”

“…Mutations in the CA domain of Gag have been shown to affect particle assembly and virion infectivity in different retroviruses, including HIV-1 [32], Simian immunodeficiency virus (SIV) [33], Mason-Pfizer monkey virus (M-PMV) [34], and RSV [35]. Several key mutants, for example the HIV-1 CA W184A and M185A cause Gag assembly defects, produce non-infectious virus particles, reduce CA dimerization and intermolecular Gag–Gag binding constants in vitro , diminish immature particle production in vivo [30, 36]; similar studies have been done with SIV [33]. In addition to introduction of disruptive site-directed mutants, interchange of residues between closely related viruses have been used to assess effects of the mutations on particle production and infectivity.…”