Mutations in Pseudorabies Virus Glycoproteins gB, gD, and gH Functionally Compensate for the Absence of gL

Schröter, Christina GND; Vallbracht, Melina GND; Altenschmidt, Jan GND; Kargoll, Sabrina GND; Fuchs, Walter GND; Klupp, Barbara GND; Mettenleiter, Thomas C. GND

Entry of herpesviruses depends on the combined action of viral glycoproteins (g)B and the heterodimeric gH/gL complex which are activated by binding of the virion to specific cellular receptors. Although gB carries signatures of a bona fide fusion protein, efficient membrane fusion requires gH/gL. However, although gB and gH/gL are essential for entry, the alphaherpesvirus Pseudorabies Virus (PrV) is capable of limited cell-to-cell spread in the absence of gL. To understand gH/gL function in more detail, the limited spread of PrV-ΔgL was used for reversion analyses by serial cell culture passages. In a first experiment an infectious gL-negative mutant was isolated in which gL function was substituted by generation of a gD-gH hybrid protein (Klupp and Mettenleiter, 1999). In a second, independent experiment PrV-ΔgLPassB4.1 was isolated, which also replicated productively without gL. Sequence analysis revealed mutations in gH, but also in gB and gD. In a transfection based fusion assay two amino acid substitutions in the N-terminal part of gHB4.1 (L70P; W103R) were found to be sufficient to compensate for lack of gL, while mutations present in gBB4.1 enhanced fusogenicity. Co-expression of gBB4.1 with the homologous gHB4.1 resulted in strongly enhanced syncytium formation, which was further augmented by truncation of the gBB4.1 C-terminal 29 amino acids. Nevertheless, gH was still required for membrane fusion. Surprisingly, co-expression of gDB4.1 blocked syncytium formation in the fusion assays, which could be attributed to a V106A substitution within the ectodomain of gDB4.1.

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Schröter, Christina / Vallbracht, Melina / Altenschmidt, Jan / et al: Mutations in Pseudorabies Virus Glycoproteins gB, gD, and gH Functionally Compensate for the Absence of gL. 2015.

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