Evolution of a Baculovirus Envelope Fusion Protein

Oregon State University, Corvallis OR

Investigators

Abstract

Baculoviruses are members of a large family of viruses that are pathogenic for insects. They are notable for their current and potential usefulness in a number of applications. For example, they are widely employed as vectors for the over-expression of proteins for both research and commercial purposes, and are also being investigated for their applicability to insect control programs. Thus, it is important to further our understanding of the biology of these viruses. This project is based on the unexpected discovery that the baculoviridae appear to be divided into two major groups based on their envelope fusion proteins. Since viral envelope fusion proteins play major roles in the infection cycle, they can be critically important components of the virion. For example, they may be involved in targeting the virion to specific receptors on the cell surface and can be directly involved in viral penetration into the host cell by inducing fusion of the viral and host cell membrane. In addition, they are often involved in virion assembly and the exit of the virus from the cell. One of these baculovirus groups (exemplified by Autographa californica multinucleocapsid nucleopolyhedrovirus [AcMNPV]) employs GP64 as its budded virion envelope fusion protein, whereas the other group (exemplified by Lymantria dispar MNPV [LdMNPV]) lacks homologs of gp64, but encodes a different envelope fusion protein (called Ld130 in LdMNPV). Surprisingly, a homolog of the LdMNPV envelope fusion protein is found in AcMNPV (orf23) and its close relatives. Preliminary data indicates that these proteins localize to membranes in infected cells. However, in contrast to Ld130, they do not appear to induce membrane fusion. This suggests that they may have lost their envelope fusion function, but are perhaps retained by the virus because they have other critical roles. The objectives of this project are to examine the role of the LdMNPV protein (Ld130) in envelope fusion, and to characterize its structure, expression, and localization in infected cells. The roles it plays in virion assembly and exit will also be investigated. Similar experiments will be conducted to determine the role that its homolog (Acorf23) plays in the AcMNPV infection cycle and to investigate its possible interaction with GP64 and with other virion proteins. It is likely that the homologs of Ld130 found in AcMNPV and its close relatives play an important role in the infectious cycle. They could be involved in viral attachment either by themselves or as co-attachment factors with GP64. In addition, if the homologs of Ld130 are membrane components as predicted, they could play a critical role in the interaction of the modified cell membrane and the nucleocapsid, thereby permitting assembly of the mature budded virus. Therefore, elucidating the role of this important family of baculovirus proteins will shed light on a number of processes critical to the biological success and utility of these viruses.