How herpes simplex virus infects cells
It’s hard to get a handle on how big, fat viruses such as herpesviruses and poxviruses infect cells because they have so many potential virus attachment proteins on their surface and these interact with a range of cellular receptors in different circumstances. However, recent research from the University of Pennsylvania has considerably improved our knowledge of the processes involved in herpes simplex virus infection.
Bimolecular complementation reveals that glycoproteins gB and gH/gL of herpes simplex virus interact with each other during cell fusion. PNAS USA 2007 104: 18718-18723
Herpes simplex virus entry into cells requires four glycoproteins, gB, gD, gH, and gL. Binding of gD to one of its receptors triggers steps requiring the core fusion proteins, gB and the gH/gL heterodimer. There is evidence that gH/gL initiates fusion of cells, but whether this complex interacts physically with gB to cause complete fusion is unknown. We used bimolecular complementation of enhanced yellow fluorescent protein (EYFP) to detect glycoprotein interactions during cell-cell fusion. The N- or C-terminal half of EYFP was fused to the C terminus of gD, gB, and gH to form six chimeric proteins. Bimolecular complementation was detected by confocal microscopy. Receptor-bearing cells cotransfected with chimeric proteins and untagged gL exhibited EYFP fluorescence, indicative of interactions between gD and gB and between gD and gH/gL. EYFP complementation did not occur in cells transfected with chimeric proteins. However, when gD was coexpressed with these other three proteins, cell-cell fusion occurred and the syncytia exhibited bright EYFP fluorescence. To separate glycoprotein expression from fusion, we transfected cells with chimeric proteins and then added soluble gD to trigger fusion. We detected fluorescent syncytia within 10 minutes, and both their number and size increased with exposure time to gD. Thus, when gD binds its receptor, the core fusion machinery is triggered to form a multiprotein complex as a step in fusion and possibly virus entry.
The herpes simplex virus receptor nectin-1 is down-regulated after trans-interaction with glycoprotein D. 2007 Virology, Dec 10
During herpes simplex virus (HSV) entry, membrane fusion occurs either on the cell surface or after virus endocytosis. In both cases, binding of glycoprotein D (gD) to a receptor such as nectin-1 or HVEM is required. In this study, we co-cultured cells expressing gD with nectin-1 expressing cells to investigate the effects of gD on nectin-1 at cell contacts. After overnight co-cultures with gD expressing cells, there was a down-regulation of nectin-1 in a range of cells which HSV enters by endocytosis. In contrast, on Vero cells, which HSV enters at the plasma membrane, nectin-1 was not down-regulated. Further analysis of B78H1-derived cells showed that nectin-1 down-regulation corresponds to the ability of gD to bind nectin-1 and is achieved by internalization and low-pH-dependent degradation of nectin-1. Moreover, gD is necessary for virion internalization in B78H1 cells expressing nectin-1. These data suggest that the determinants of gD-mediated internalization of nectin-1 may direct HSV to an endocytic pathway during entry.
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Tags: Biology, Health, Medicine, Microbiology, Science, Virology
