title: X-ray crystallographic determination of the structure of the influenza C virus haemagglutinin-esterase-fusion glycoprotein.
abstract: The structure of the haemagglutinin-esterase-fusion (HEF) glycoprotein from influenza C virus has been determined to 3.2 A resolution by X-ray crystallography. A synthetic mercury-containing esterase inhibitor and receptor analogue, 9-acetamidosialic acid alpha-thiomethylmercuryglycoside, was designed as the single isomorphous heavy-atom derivative. The asymmetric unit of one crystal form (form I; P4322, a = b = 155.4, c = 414.4 A) contained an HEF trimer. Six mercury sites identifying the three haemagglutination and three esterase sites were located by difference Patterson map analysis of a 6.5 A resolution derivative data set. These positions defined the molecular threefold-symmetry axis of the HEF trimer. A molecular envelope was defined by averaging a 7.0 A resolution electron-density map, phased by single isomorphous replacement (SIR), about the non-crystallographic threefold-symmetry axis. Iterative non-crystallographic symmetry averaging in real space, solvent flattening and histogram matching were used to extend the phases to 3.5 A resolution. Molecular replacement of the model into a second crystal form (form II; P43212, a = b = 217.4, c = 421.4 A) containing two HEF trimers per asymmetric unit permitted iterative ninefold averaging of the electron density. The 3.5 A electron-density map allowed an unambiguous tracing of the polypeptide chain and identification of N-linked carbohydrates. The model has been refined by least squares to 3.2 A resolution (Rfree = 26.7%).
authors.affiliation: Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA 02138, USA.
authors.forename: X
authors.initials: X
authors.lastname: Zhang
authors.forename: P B
authors.initials: PB
authors.lastname: Rosenthal
authors.forename: F
authors.initials: F
authors.lastname: Formanowski
authors.forename: W
authors.initials: W
authors.lastname: Fitz
authors.forename: C H
authors.initials: CH
authors.lastname: Wong
authors.forename: H
authors.initials: H
authors.lastname: Meier-Ewert
authors.forename: J J
authors.initials: JJ
authors.lastname: Skehel
authors.forename: D C
authors.initials: DC
authors.lastname: Wiley
mesh_terms: D000115:Acetylesterase / Q000737:chemistry*; D001665:Binding Sites; D018360:Crystallography, X-Ray; D006023:Glycoproteins / Q000737:chemistry*; D006389:Hemagglutinins, Viral / Q000737:chemistry*; D009982:Gammainfluenzavirus / Q000201:enzymology*; D008628:Mercury / Q000737:chemistry; D008958:Models, Molecular; D011487:Protein Conformation; D014760:Viral Fusion Proteins / Q000737:chemistry*
chemical_list: D006023:Glycoproteins; D006389:Hemagglutinins, Viral; D014760:Viral Fusion Proteins; C060814:hemagglutinin esterase; D000115:Acetylesterase; D008628:Mercury