Date Published: February 27, 2014
Publisher: Public Library of Science
Author(s): Daniel Aberle, Claudia Muhle-Goll, Jochen Bürck, Moritz Wolf, Sabine Reißer, Burkhard Luy, Wolfgang Wenzel, Anne S. Ulrich, Gregor Meyers, Félix A. Rey.
Erns is an essential virion glycoprotein with RNase activity that suppresses host cellular innate immune responses upon being partially secreted from the infected cells. Its unusual C-terminus plays multiple roles, as the amphiphilic helix acts as a membrane anchor, as a signal peptidase cleavage site, and as a retention/secretion signal. We analyzed the structure and membrane binding properties of this sequence to gain a better understanding of the underlying mechanisms. CD spectroscopy in different setups, as well as Monte Carlo and molecular dynamics simulations confirmed the helical folding and showed that the helix is accommodated in the amphiphilic region of the lipid bilayer with a slight tilt rather than lying parallel to the surface. This model was confirmed by NMR analyses that also identified a central stretch of 15 residues within the helix that is fully shielded from the aqueous layer, which is C-terminally followed by a putative hairpin structure. These findings explain the strong membrane binding of the protein and provide clues to establishing the Erns membrane contact, processing and secretion.
The genus Pestivirus belongs to the family Flaviviridae, together with the genera Hepacivirus, Flavivirus and Pegivirus. It represents a group of economically important animal viruses like classical swine fever virus (CSFV) and bovine viral diarrhea virus (BVDV) . The economical damage caused by these viruses is not only due to the acute infection of the animals, but stems also from their ability to cause persistent infection of the fetus after infection of a pregnant animal , . If an infection of the fetus by BVDV is established, a persistently infected calf is born. This calf often shows no signs of disease, but sheds huge amounts of infectious virus particles throughout its whole life, which leads to an efficient spreading of the virus.
Erns represents one of the four known pestiviral structure proteins. The protein is crucial for the formation of infectious viral particles and plays a major role also during the infection of cells. But aside from this elementary function, Erns represents also a virulence factor of pestiviruses. In this context it is important that Erns has an intrinsic RNase activity. RNases are only very rarely found in RNA viruses , and to our knowledge the pestivirus Erns is the only viral structural protein displaying such enzymatic activity. This RNase activity is crucial for the virulence of the virus. It could be shown that pestiviruses containing an RNase negative Erns protein are viable and able to replicate to nearly wild type virus titers, but are attenuated in their natural hosts , . Most importantly, the RNase activity is a major factor for establishing a persistent infection upon transplacental infection of the fetus in a pregnant host animal .