title: Structural analysis of the extracellular domain of vaccinia virus envelope protein, A27L, by NMR and CD spectroscopy.
abstract: This study presents the molecular structure of the extracellular domain of vaccinia virus envelope protein, A27L, determined by NMR and CD spectroscopy. A recombinant protein, eA27L-aa, containing this domain in which cysteines 71 and 72 were replaced with alanine, was constructed to prevent self-assembly due to intermolecular disulfide bonds between these two cysteines. The soluble eA27L-aa protein forms an oligomer resembling that of A27L on vaccinia virions. Heteronuclear correlation NMR spectroscopy was carried out on eA27L-aa in the presence or absence of urea to determine backbone resonance assignments. Chemical shift index (CSI) propensity analysis showed that eA27L-aa has two distinct structural domains, a relatively flexible 22-amino acid random coil in the N-terminal region and a fairly rigid alpha-helix structure in the remainder of the structure. Binding interaction studies using isothermal titration calorimetry suggest that a 12-amino acid lysine/arginine-rich segment in the N-terminal region is responsible for glycosaminoglycan binding. The rigid alpha-helix portion of eA27L-aa is probably involved in the intrinsic self-assembly, and CSI propensity analysis suggests that region N37-E49, with a residual alpha-helix tendency, is probably the self-assembly core. Self-assembly was ascribed to three hydrophobic leucine residues (Leu(41), Leu(45), and Leu(48)) in this segment. The folding mechanism of eA27L-aa was analyzed by CD spectroscopy, which revealed a two-step transition with a Gibbs free energy of 2.5 kcal/mol in the absence of urea. Based on these NMR and CD studies, a residue-specific molecular model of the extracellular domain of A27L is proposed. These studies on the molecular structure of eA27L-aa will help in understanding how vaccinia virus enters cells.
authors.affiliation: Institute of Biochemistry, National Yang-Ming University, Shih-pai, Taipei 11221, Taiwan.
authors.forename: Ta-Hsien
authors.initials: TH
authors.lastname: Lin
authors.forename: Chih-Ming
authors.initials: CM
authors.lastname: Chia
authors.forename: Jye-Chian
authors.initials: JC
authors.lastname: Hsiao
authors.forename: Wen
authors.initials: W
authors.lastname: Chang
authors.forename: Chiao-Chu
authors.initials: CC
authors.lastname: Ku
authors.forename: Shang-Cheng
authors.initials: SC
authors.lastname: Hung
authors.forename: Der-Lii M
authors.initials: DL
authors.lastname: Tzou
mesh_terms: D002151:Calorimetry; D002942:Circular Dichroism; D006493:Heparin / Q000378:metabolism; D019906:Nuclear Magnetic Resonance, Biomolecular; D011485:Protein Binding; D017433:Protein Structure, Secondary; D014616:Vaccinia virus / Q000737:chemistry*; D014764:Viral Proteins / Q000737:chemistry* / Q000378:metabolism
chemical_list: C110360:A27L protein, Orthopoxvirus; D014764:Viral Proteins; D006493:Heparin