title: A conserved internal hydrophobic domain mediates the stable membrane integration of the dengue virus capsid protein.
abstract: The mature flavivirus capsid protein (virion C) is commonly thought to be free in the cytoplasm of infected cells and to form a nucleocapsid-like complex with genomic RNA in mature virus particles. There is little sequence conservation among flavivirus virion C proteins, but they are similar in size (e.g., 99 amino acids [aa] for the dengue-4 [DEN4] C) and in bearing a net positive charge. In addition, we noted that C contained a conserved internal hydrophobic segment (spanning aa 45-65 in the DEN4 C). Results of in vivo expression and in vitro translation of wt and mutant forms of the DEN4 virion C demonstrated that the conserved internal hydrophobic segment in the DEN C functioned as a membrane anchor domain. Signal peptide function of this segment was also suggested by its requirement for the entry of C into membranes. Virion C was integrated in membranes in a "hairpin" conformation; positively charged segments amino- and carboxy-terminal to the hydrophobic signal-anchor segment were accessible to protease digestion in the "cytoplasm." The net positive charge in the amino-terminal extramembraneous portion of C (aa 1-44) was one determinant of the hairpin membrane orientation; a conserved positively charged residue within the hydrophobic segment (Arg-54 in the DEN4 C) was not.
authors.affiliation: Laboratory of Vector-borne Virus Diseases, Food and Drug Administration, Bethesda, Maryland 20892, USA.
authors.forename: L
authors.initials: L
authors.lastname: Markoff
authors.forename: B
authors.initials: B
authors.lastname: Falgout
authors.forename: A
authors.initials: A
authors.lastname: Chang
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D002213:Capsid / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism / Q000821:virology; D017124:Conserved Sequence; D003716:Dengue Virus / Q000235:genetics / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism; D008969:Molecular Sequence Data; D016296:Mutagenesis