Biology subjects

Markosyan, R. M.

Publications and source records attributed to Markosyan, R. M..

2 recordsLinked to original sources

bioRxiv2025

SERINC5 co-expressed with HIV-1 Env or present in a target membrane destabilizes small fusion pores leading to their collapse

SERINC5 is a multipass membrane protein that reduces infectivity of retroviruses and other enveloped viruses through incorporation into budding virions and inhibiting viral fusion. Several modes of anti-HIV activity of SERINC5 have been reported, including binding to Env glycoprotein, induction of conformational changes and destabilization of Env, as well as disruption of trans-membrane asymmetry of viral envelope. All these reported anti-HIV mechanisms involve SERINC5 incorporation into progeny virions, while there is very little information regarding a potential antiviral activity of SERINC5 in target cells. Here, we show that SERINC5 expressed in target cells efficiently inhibits fusion with cells expressing sensitive but not resistant HIV-1 strains. We show that this activity does not result from downregulation of CD4 or coreceptors on target cells or interference with the formation of ternary Env/CD4/coreceptor complexes. We further demonstrate that SERINC5 destabilizes small fusion pores causing their collapse and that this block can be rescued by incorporation of phosphatidylserine to either effector (Env-expressing) or target cells. Interestingly, we did not detect a significant reduction of HIV-1 pseudovirus fusion with SERINC5 expressing target cells, while virus-mediated cell-cell fusion (fusion-from-without) was inhibited, suggesting a potential role of virus entry pathway in SERINC5 restriction. Collectively, our results reveal a novel mechanism of inhibition of HIV-1 fusion by SERINC5 through destabilization of small fusion pores in a manner that depends on lipid composition. ImportanceSERINC5 incorporates into virions produced by infected cells and inhibits viral fusion with target cells through a poorly understood mechanism. Here, we show that SERINC5 blocks HIV-1 Env mediated cell fusion when expressed in either effector (Env-expressing) or target cells. Inhibition of Env-mediated fusion by SERINC5 expressed in target cells is not through reduction in receptor or coreceptor expression or interference with Envs ability to engage a requisite number of receptors and coreceptors. We demonstrate that the block of fusion is at a post-hemifusion stage of small fusion pores that collapse when SERINC5 is present in effector or target membrane and that this block is rescued by incorporation of specific anionic lipids, such as phosphatidylserine. These findings reveal a previously unappreciated mode of HIV-1 restriction through destabilization of small fusion pores that occurs irrespective of SERINC5 localization in either of fusing membranes.

microbiology↗

bioRxiv2021

The late endosome-resident lipid bis(monoacylglycero)phosphate is a cofactor for Lassa virus fusion

Arenavirus entry into host cells occurs through a low pH-dependent fusion with late endosomes that is mediated by the viral glycoprotein complex (GPC). The mechanisms of GPC-mediated membrane fusion and of virus targeting to late endosomes are not well understood. To gain insights into arenavirus fusion, we examined cell-cell fusion induced by the Old World Lassa virus (LASV) GPC complex. LASV GPC-mediated cell fusion is more efficient and occurs at higher pH in cells expressing human LAMP1 compared to cells lacking this cognate receptor, but this receptor is not absolutely required for virus entry. GPC-induced fusion progresses through the same lipid intermediates as fusion mediated by other viral glycoproteins - a lipid curvature-sensitive intermediate upstream of hemifusion and a hemifusion intermediate downstream of acid-dependent steps that can be arrested in the cold. Importantly, GPC-mediated fusion is specifically augmented by an anionic lipid, bis(monoacylglycero)phosphate (BMP), which is highly enriched in late endosomes. We show that BMP promotes late steps of LASV fusion downstream of hemifusion - the formation and enlargement of fusion pores. This lipid also specifically promotes cell fusion mediated by GPC of the unrelated New World Junin arenavirus. The BMP-dependence of post-hemifusion stages of arenavirus fusion suggests that these viruses evolved to use this lipid as a cofactor to direct virus entry to late endosomes. Author SummaryPathogenic arenaviruses pose a serious health threat. The viral envelope glycoprotein GPC mediates attachment to host cells and drives virus entry via endocytosis and low pH-dependent fusion within late endosomes. Understanding the host factors and processes that are essential for arenavirus fusion may identify novel therapeutic targets. To delineate the mechanism of arenavirus entry, we examined cell-cell fusion induced by the Old World Lassa virus GPC proteins at low pH. Lassa virus fusion was augmented by the LAMP1 receptor and progressed through lipid curvature-sensitive intermediates, such as hemifusion (merger of contacting leaflets of viral and cell membrane without the formation of a fusion pore). We found that most GPC-mediated fusion events were off-path hemifusion structures and that the transition from hemifusion to full fusion and fusion pore enlargement were specifically promoted by an anionic lipid, bis(monoacylglycero)phosphate, which is highly enriched in late endosomes. This lipid also specifically promotes fusion of unrelated New World Junin arenavirus. Our results imply that arenaviruses evolved to use bis(monoacylglycero)phosphate to enter cells from late endosomes.

microbiology↗