Structure of the Membrane Anchor of Pestivirus Glycoprotein Erns, a Long Tilted Amphipathic Helix

Abstract

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.

Host-derived apolipoproteins play comparable roles with viral secretory proteins Erns and NS1 in the infectious particle formation of Flaviviridae

“…E rns contains an amphipathic helix domain of 61 residues for membrane binding instead of a transmembrane [12]. Although the current study revealed that the C-terminal helix domain of E rns plays a crucial role in the infectious particle formation, the helix domains from exchangeable apolipoproteins and CAMP have been shown to play similar roles in particle formation [10, 11].…”

The Molecular Biology of Pestiviruses

“…Within this segment, a stretch of 15 amino acids shows no exchange of N-bound protons with water. These residues have either no water contact indicating complete insertion into the membrane or are fixed in a very stable helix forming upon contact with the lipid bilayer so that the N-linked protons are trapped in a rigid structure (Aberle et al, 2014) (Fig. 7).…”

“…Image was rendered with PyMOL using the structure deposited in the PDB database (4DVK) (PyMOL: The PyMOL Molecular Graphics System, Version 1.7.4 Schrödinger, LLC). (C) An MD simulation of the E rns membrane anchor taken fromAberle et al (2014).…”

Structural characterization of a C-terminally truncated E5 oncoprotein from papillomavirus in lipid bilayers

“…OCD is a powerful tool for studying the orientation of membrane-active peptides and protein segments in membranes (Lange et al, 2007;Bürck et al, 2008;Strandberg et al, 2008;Wadhwani et al, 2008Wadhwani et al, , 2012Wadhwani et al, , 2014Nolandt et al, 2009;Windisch et al, 2010;Heinzmann et al, 2011;Klein et al, 2012;Muhle-Goll et al, 2012;Steinbrecher et al, 2012;Aberle et al, 2014;Fanghänel et al, 2014). For α-helices, the OCD band at 208 nm can be used to estimate the helix tilt angle relative to the membrane normal (Wu et al, 1990).…”