The domains required to direct core proteins of hepatitis C virus and GB virus-B to lipid droplets share common features with plant oleosin proteins.
In mammalian tissue culture cells, the core protein of hepatitis C virus (HCV) is located at the surface of lipid droplets, which are cytoplasmic structures that store lipid. The critical amino acid sequences necessary for this localization are in a region of core protein that is absent in flavi- and pestiviruses, which are related to HCV. From our sequence comparisons, this region in HCV core was present in the corresponding protein of GBV-B, another virus whose genomic sequence has significant similarity to HCV. Expression of the putative GBV-B core protein revealed that it also was directed to lipid droplets. By extending the comparisons to cellular proteins, there were amino acid sequence similarities between the domains for lipid droplet association in HCV core and plant oleosin proteins. To determine whether these similarities were related functionally, an oleosin encoded by the Brassica napus bniii gene was expressed in different mammalian cell lines, where it retained the capacity to bind to lipid droplets. Analysis of deletion mutants indicated that the critical region within the protein required for this localization was the same for both plant and mammalian cells. A common feature in the viral and plant sequences was a motif containing proline residues. Mutagenesis of these residues in HCV core and plant oleosin abolished lipid droplet association. Finally, the domain within HCV core required for binding to lipid droplets could substitute for the equivalent domain in oleosin, further indicating the functional relatedness between the viral and plant sequences. These studies identify common features in disparate proteins that are required for lipid droplet localization.
Hope
R Graham
RG
MRC Virology Unit, Institute of Virology, Church Street, Glasgow G11 5JR and School of Applied Sciences, University of Glamorgan, Trefforrest, Cardiff CF37 1DL, United Kingdom.
Murphy
Denis J
DJ
McLauchlan
John
J
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001937:Brassica / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D006224:Cricetinae; D018744:DNA, Plant; D018067:Flaviviridae / Q000378:metabolism*; D019084:Fluorescent Antibody Technique, Indirect; D017343:Genes, Plant; D016174:Hepacivirus / Q000378:metabolism*; D050356:Lipid Metabolism; D008565:Membrane Proteins; D008969:Molecular Sequence Data; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D014758:Viral Core Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
D002352:Carrier Proteins; D018744:DNA, Plant; D008565:Membrane Proteins; D010940:Plant Proteins; D014758:Viral Core Proteins; C448199:oleosin Bn-III protein, Brassica napus