VIRUS-SPECIFIC INTERACTION BETWEEN THE HUMAN CYTOMEGALOVIRUS MAJOR CAPSID PROTEIN AND THE C-TERMINUS OF THE ASSEMBLY PROTEIN-PRECURSOR

We previously identified a minimal 12-amino-acid domain in the C termi nus of the herpes simplex virus type 1 (HSV-1) scaffolding protein whi ch is required for interaction with the HSV-1 major capsid protein. An alpha-helical structure which maximizes the hydropathicity of the min imal domain is required for the interaction. To address whether cytome galovirus (CMV) utilizes the same strategy for capsid assembly, severa l glutathione S-transferase fusion proteins to the C terminus of the C MV assembly protein precursor were produced and purified from bacteria l cells. The study shelved that the glutathione S-transferase fusion c ontaining 16 amino acids near the C-terminal end was sufficient to int eract with the major capsid protein. Interestingly, no cross-interacti on between HSV-1 and CMV could be detected. Mutation analysis revealed that a three-aminoacid region at the N-terminal side of the central P he residue of the CMV interaction domain played a role in determining the viral specificity of the interaction. When this region was convert ed so as to correspond to that of HSV-1, the CMV assembly protein doma in lost its ability to interact with the CMV major capsid protein but gained full interaction with the HSV-1 major capsid protein. To addres s whether the minimal interaction domain of the CMV assembly protein f orms an alpha-helical structure similar to that in HSV-1, peptide comp etition experiments were carried out. The results showed that a cyclic peptide derived from the interaction domain with a constrained alpha- helical structure competed for interaction with the major capsid prote in much more efficiently than the unconstrained linear peptide. In con trast, a cyclic peptide containing an Ala substitution for the critica l Phe residue did not compete for the interaction at all. The results of this study suggest that (i) CMV may have developed a strategy simil ar to that of HSV-1 for capsid assembly; (ii) the minimal interaction motif in the CMV assembly protein requires an alpha-helix for efficien t interaction with the major capsid protein; and (iii) the Phe residue in the CMV minimal interaction domain is critical for interaction wit h the major capsid protein.