Structure-function analysis of the coxsackievirus protein 3A: identification of residues important for dimerization, viral rna replication, and transport inhibition

The coxsackievirus B3 3A protein forms homodimers and plays important roles in both viral RNA (vRNA) replication and the viral inhibition of intracellular protein transport. The molecular determinants that are required for each of these functions are yet poorly understood. Based on the NMR structure of the closely related poliovirus 3A protein, a molecular model of the coxsackievirus B3 3A protein was constructed. Using this structural model, specific mutants were designed to study the structure-function relationship of 3A. The mutants were tested for their capacity to dimerize, support vRNA replication, and block protein transport. A hydrophobic interaction between the monomers and an intermolecular salt bridge were identified as major determinants required for dimerization. We show that dimerization is important for both efficient vRNA replication and inhibition of protein transport. In addition, determinants were identified that were not required for dimerization but that were essential for either one of the biological functions of 3A. The combination of the in silico and in vivo results obtained in this study provides important insights in both the structural and functional aspects of 3A.