Vaccinia virus encodes at least eight proteins that are modified post-translationally by the addition of a 16-carbon saturated fatty acid through thioester linkage to cysteine residues. This is referred to as palmitylation of proteins. The purpose of this work was to gain an understanding of palmitylation, focusing on what defined the substrate for the modification, and the biological relevance of protein palmitylation in the vaccinia virus life cycle.
A systematic approach was taken to identify the genes in vaccinia virus that encode these proteins. We found that vaccinia virus palmitylproteins are of the "late" temporal class, associate with intracellular membranes, and are specific for a particular form of the infectious virion. These criteria were used to narrow the number of genes expressed by vaccinia virus that potentially encode palmitylproteins. The "candidate" palmitylprotein genes were cloned and transiently expressed in mammalian tissue culture cells and analyzed for incorporation of palmitic acid. In addition to three previously identified vaccinia virus palmitylproteins, three new palmitylproteins were identified. The six known palmitylprotein genes were mutated to determine the site of modification, leading to the identification of the modification site for four of the six proteins.
One of the proteins, p37, was analyzed further for biological significance of the palmitate modification. A recombinant vaccinia virus was constructed that did not express the wild-type palmitylated form of p37, but expressed a nonpalmitylated form of the protein instead. This virus was severely inhibited from proceeding past a particular morphogenetic stage, leading to an attenuated phenotype in tissue culture systems. Although the expression of the nonpalmitylated protein appeared normal compared to the wild-type protein, the lack of the palmityl moiety resulted in the loss of a targeting signal that directed the protein to its normal intracellular location.
By this work, significant contributions have been made toward understanding the process of protein palmitylation. We have identified, at least for vaccinia virus, primary structural determinants specifying the modification, leading to the identification of a palmitylation motif. Considering the attenuated phenotype of the mutant virus, our conclusion is that palmitylation is necessary for biological function, at least for p37. / Graduation date: 1999
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/33183 |
| Date | 29 April 1999 |
| Creators | Grosenbach, Douglas W. |
| Contributors | Hruby, Dennis E. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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