title: Trimeric transmembrane domain interactions in paramyxovirus fusion proteins: roles in protein folding, stability, and function.
abstract: Paramyxovirus fusion (F) proteins promote membrane fusion between the viral envelope and host cell membranes, a critical early step in viral infection. Although mutational analyses have indicated that transmembrane (TM) domain residues can affect folding or function of viral fusion proteins, direct analysis of TM-TM interactions has proved challenging. To directly assess TM interactions, the oligomeric state of purified chimeric proteins containing the Staphylococcal nuclease (SN) protein linked to the TM segments from three paramyxovirus F proteins was analyzed by sedimentation equilibrium analysis in detergent and buffer conditions that allowed density matching. A monomer-trimer equilibrium best fit was found for all three SN-TM constructs tested, and similar fits were obtained with peptides corresponding to just the TM region of two different paramyxovirus F proteins. These findings demonstrate for the first time that class I viral fusion protein TM domains can self-associate as trimeric complexes in the absence of the rest of the protein. Glycine residues have been implicated in TM helix interactions, so the effect of mutations at Hendra F Gly-508 was assessed in the context of the whole F protein. Mutations G508I or G508L resulted in decreased cell surface expression of the fusogenic form, consistent with decreased stability of the prefusion form of the protein. Sedimentation equilibrium analysis of TM domains containing these mutations gave higher relative association constants, suggesting altered TM-TM interactions. Overall, these results suggest that trimeric TM interactions are important driving forces for protein folding, stability and membrane fusion promotion.
authors.affiliation: From the Department of Molecular and Cellular Biochemistry, University of Kentucky, Lexington, Kentucky 40536.
authors.forename: Everett Clinton
authors.initials: EC
authors.lastname: Smith
authors.forename: Stacy E
authors.initials: SE
authors.lastname: Smith
authors.forename: James R
authors.initials: JR
authors.lastname: Carter
authors.forename: Stacy R
authors.initials: SR
authors.lastname: Webb
authors.forename: Kathleen M
authors.initials: KM
authors.lastname: Gibson
authors.forename: Lance M
authors.initials: LM
authors.lastname: Hellman
authors.forename: Michael G
authors.initials: MG
authors.lastname: Fried
authors.forename: Rebecca Ellis
authors.initials: RE
authors.lastname: Dutch
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism* / Q000821:virology; D002522:Chlorocebus aethiops; D008561:Membrane Fusion; D008969:Molecular Sequence Data; D017510:Protein Folding; D055503:Protein Multimerization; D055550:Protein Stability; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D014709:Vero Cells; D014760:Viral Fusion Proteins / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D014760:Viral Fusion Proteins
keywords: Fusion Protein; Membrane Fusion; Negative-strand RNA Viruses; Transmembrane Domain; Virus; Virus Entry