Arenavirus Stable Signal Peptide Is the Keystone Subunit for Glycoprotein Complex Organization

Bederka, Lydia H.; Bonhomme, Cyrille J.; Ling, Emily L.; Buchmeier, Michael J.

Signal peptides, although diverse in their amino acid compositions, share a similar organization (25) . Each signal peptide has a variable-length amino terminus, a hydrophobic center region, and a carboxyl terminus, including the signal peptidase cleavage site. In order to directly analyze the signal peptide, we took advantage of the variable amino-terminal region by inserting an HA epitope within this SSP region while in the context of the fulllength glycoprotein open reading frame (HA SSP GPC). HA SSP GPC was an expansion of a tool previously used for Junín SSP membrane topology characterization, though in those studies SSP was expressed in trans with the remaining portion of the glycoprotein (37) . Insertion of the HA epitope did not alter glycoprotein trafficking, as SKI-1/S1P-deficient cells were unable to cleave GPC into mature GP1 and GP2 unless functional SKI-1/S1P was supplemented in trans (data not shown). This HA SSP GPC behaved at wild-type levels in terms of its expression, GP2 cleavage, and plasma membrane localization. Additionally, this HA SSP GPC allowed us to target experiments, both biochemical and with microscopy, directly focusing on SSP while eliminating the technicalities of cotransfection.