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J Biol Chem. 2010 Mar 19;285(12):8572-84. doi: 10.1074/jbc.M109.083394. Epub 2010 Jan 21.

A new type of signal peptidase cleavage site identified in an RNA virus polyprotein.

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Institut für Immunologie, Friedrich-Loeffler-Institut, Paul-Ehrlich-Strasse 28, D-72001 Tübingen, Germany.


Pestiviruses, a group of enveloped positive strand RNA viruses belonging to the family Flaviviridae, express their genes via a polyprotein that is subsequently processed by proteases. The structural protein region contains typical signal peptidase cleavage sites. Only the site at the C terminus of the glycoprotein E(rns) is different because it does not contain a hydrophobic transmembrane region but an amphipathic helix functioning as the E(rns) membrane anchor. Despite the absence of a hydrophobic region, the site between the C terminus of E(rns) and E1, the protein located downstream in the polyprotein, is cleaved by signal peptidase, as demonstrated by mutagenesis and inhibitor studies. Thus, E(rns)E1 is processed at a novel type of signal peptidase cleavage site showing a different membrane topology. Prevention of glycosylation or introduction of mutations into the C-terminal region of E(rns) severely impairs processing, presumably by preventing proper membrane interaction or disturbing a conformation critical for the protein to be accepted as a substrate by signal peptidase.

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