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From 2012.igem.org

Modifying the outside of a VLP

Introduction

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The monomers of virus-like particles (VLPs) have been subject to many modifications of which some are aimed at changing the appearance of the particle. By changing the outside, the VLP acquires new properties which has been used mainly in vaccine development (ref 5epis and others). The modification we pursue is adding a coil to the protein subunits, at any location that is exposed on the outside of the VLP. This can be a fusion to a C or N-terminal, but a modification in the loop is possible as well. The goal of the coil is to serve as a docking sites for ligands which are modified to contain a coil subunit. A coil on the outside plays a rather important role expanding the applications of VLPs. It forms the link between the VLP and a functional group, such as a ligand or antigen.

PLRV and TuYV

The Potato Leaf Roll Virus (PLRV) and Turnip Yellows Virus (TuYV) have a very interesting feature. Part of the subunits is expressed with a read-through products which form spikes-like structures on the outside of the VLP. The idea is to replace the spike by a k-coil. Because this part is not involved in formation of the VLP, it will not change the wild-type properties of the particle during formation. Besides, there is only one insert needed, because the read-through does not occur with each translation.

Hepatitis B

A loop exposed on the outside of Hepatitis B is known to accept modifications and for VLPs still [ref to research about inserts]. Formation is improved when a mixture is made from wt and modified subunits. There is one problem concerning the insertion of the k-coil in the external loop: The coil will be bended [link to in silico], while it is designed to be linear. This can be solved by inserting a protease specific site next to the coil. In this way, the coil can be linearized by cutting the protein after VLP formation. This exposes the coil in a linearized formation, allowing attachment of the ligand.