Envelope
The HCV envelope glycoproteins consist of the E1 and E2 glycoproteins noncovalently associated as a heterodimer. This E1/E2 glycoprotein heterodimer is embedded in the host-derived lipid membrane and together forms the HCV envelope. The envelope glycoproteins form a higher order oligomeric structure consisting of trimers of E1/E2 heterodimers (three groups of heterodimers); the trimers can then assemble into pentamers (five groups of trimers). Structurally, the hypervariable region in the E2 protein shields the E1 protein from the immune system. The envelope proteins play a role in host receptor binding, endosome-lipid membrane fusion, and assembly. The E1 protein is approximately 192 amino acids long and the E2 protein is approximately 363 amino acids long. The host-derived lipid membrane component of the envelope is composed primarily of cholesterol, cholesteryl esters, phosphatidylcholine, and sphingomyelin.