The cleavage of p62, the precursor of E2 and E3, is an early and continuous event in Semliki Forest virus-infected Aedes albopictus cells

Abstract

The cleavage of p62 of Semliki Forest virus (SFV) in C6/36 (Aedes albopictus) cells was investigated by pulse-chase labeling experiments and analysis of the sugar side chain of E1 using endoglycosidases. Similar to vertebrates, E1, E2, and p62 are transported as complexes in C6/36 cells. This observation allows the use of E1 as a positional marker for the transport and processing of E2 and p62. The oligosaccharide on the viral spike E1 protein was modified first to an Endo-D-sensitive (35 min) and then to an Endo-H-resistant structure (55 min), whereas the oligosaccharides of p62 remained sensitive towards Endo-H the whole time. E2 could be detected already at 10-20 min post synthesis, suggesting that p62 cleavage starts early, probably before the protein has been transported to the Golgi apparatus. This is in contrast to the cleavage taking place later mainly near the plasma membrane of higher eukaryotes. The spike proteins finally appeared in extracellular virions after about 70-90 min post synthesis.