Identification of a single amino acid residue which is critical for the interaction between HSV-1 inner tegument proteins pUL36 and pUL37

The herpes simplex virus type 1 (HSV-1) structural tegument proteins pUL36 and pUL37 are essential for secondary envelopment during the egress of viral particles. For this study, scanning alanine mutagenesis of HSV-1 pUL37, in combination with yeast two-hybrid, identified pUL37 residue D631 as a major determinant for binding of pUL36. Further analysis of the binding of this pUL37 mutant to pUL36 by coimmunoprecipitation assay confirmed the role of pUL37 D631 in mediating binding of pUL36. A trans-complementation assay using pUL37 deletion virus FRΔUL37 was then carried out, where pUL37 wild type or D631A were provided in trans. For pUL37 D631A, a significant reduction in virus titer was observed compared to that seen when pUL37 wild type was present. The results presented here underline the crucial role of the pUL36/pUL37 interaction in replication of HSV-1 and indicate a critical role for pUL37 D631 in mediating this interaction.