Abstract
The herpes simplex virus type 1 (HSV-1) glycoprotein N (gN/UL49.5) is a type I transmembrane protein conserved throughout the herpesvirus family. gN is a resident of the endoplasmic reticulum that in the presence of gM is translocated to the trans Golgi network. gM and gN are covalently linked by a single disulphide bond formed between cysteine 46 of gN and cysteine 59 of gM. Exit of gN from the endoplasmic reticulum requires the N-terminal core of gM composed of eight transmembrane domains but is independent of the C-terminal extension of gM. Co-transport of gN and gM to the trans Golgi network also occurs upon replacement of conserved cysteines in gM and gN, suggesting that their physical interaction is mediated by covalent and non-covalent forces. Deletion of gN/UL49.5 using bacterial artificial chromosome (BAC) mutagenesis generated mutant viruses with wild-type growth behaviour, while full deletion of gM/UL10 resulted in an attenuated phenotype. Deletion of gN/UL49.5 in conjunction with various gM/UL10 mutants reduced average plaque sizes to the same extent as either single gM/UL10 mutant, indicating that gN is nonessential for the function performed by gM. We propose that gN functions in gM-dependent as well as gM-independent processes during which it is complemented by other viral factors.
Highlights
Herpesviruses have evolved a life cycle that strongly depends on several membrane-associated processes [1,2]
A short N-terminal signal peptide is believed to mediate its co-translational insertion into the endoplasmic reticulum (ER), resulting in the N-terminal domain exposed to the ER lumen
herpes simplex virus type 1 (HSV-1) gM is a type III membrane protein containing 8 predicted transmembranespanning domains with both the N- and C-terminal ends oriented towards the cytosol (Figure 1B)
Summary
Herpesviruses have evolved a life cycle that strongly depends on several membrane-associated processes [1,2]. HSV-1 gN is encoded by the ORF UL49.5 and comprised of 91 amino acids (aa). It is a type I transmembrane protein with a single transmembrane-spanning domain. HSV-1 gM, a type III transmembrane protein encoded by the ORF UL10, is predicted to contain. HSV-1 gM, a type III transmembrane protein encoded by the ORF UL10, is predicted to eight membrane-spanning domains with both. Reported to be formedto between several gM and seems to partner seems to partner with gN to modulate the fusion machinery GN and gM physically interact via their N-terminal domains, and this covalent and non-covalent forces.
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