Role of ORF4 in Hepatitis E virus regulation: analysis of intrinsically disordered regions

Hepatitis E virus (HEV) is one of the causative agents of liver infections. The essential open reading frame 4 (ORF4) encoded protein role in HEV regulation remains undetermined. Intrinsically disordered protein regions (IDPRs)/intrinsically disordered protein (IDPs) in viral proteomes are linked with virus’s pathogenicity and infectivity. Therefore, in the present study, we have examined the unstructured/disordered regions of ORF4 proteins by analyzing the prevalence of intrinsic disorder. The intrinsic disorder propensity analysis of ORF4 proteins revealed JN167538 (Rat) as a structured protein, LC057248 (HEV) and LC177791 (Ferret) as moderately disordered proteins and KU168733 (Human) as a highly disordered protein, categorizing them as ORDP, IDPRs and IDR, respectively. All the ORF4 proteins consisted of molecular recognition features (MoRFs), i.e., intrinsic disorder-based protein–protein interaction (PPI) sites used by proteins to interact with specific partners, in addition to several nucleotide-binding sites. As IDPR and IDP, in conjunction with molecular recognition (PPI, RNA binding and DNA binding), our results signified the ORF4 protein’s interactions with the host membranes and further viral infection. In particular, as IDP, the ORF4 protein (Human) could possibly contribute to viral replication through PPIs. The presence of various disordered-based phosphorylation sites further signified the role of ORF4 proteins in various biological processes, such as post-translational modifications (/PTMs). Furthermore, structure-based analyses of ORF4 proteins revealed it as a multifunctional-associated protein, due to its involvement in various binding and catalytic activities. Collectively, data from this comprehensive investigation suggested ORF4 protein’s role in regulation and pathogenesis of HEV.