Determination of the Disulfide Bond Arrangement of Newcastle Disease Virus Hemagglutinin Neuraminidase CORRELATION WITH A b-SHEET PROPELLER STRUCTURAL FOLD PREDICTED FOR Paramyxoviridae ATTACHMENT PROTEINS*□S

Disulfide bonds stabilize the structure and functions of the hemagglutinin neuraminidase attachment glycoprotein (HN) of Newcastle disease virus. Until this study, the disulfide linkages of this HN and structurally similar attachment proteins of other members of the paramyxoviridae family were undefined. To define these linkages, disulfide-linked peptides were produced by peptic digestion of purified HN ectodomains of the Queensland strain of Newcastle disease virus, isolated by reverse phase high performance liquid chromatography, and analyzed by mass spectrometry. Analysis of peptides containing a single disulfide bond revealed Cys-Cys and Cys-Cys linkages and that HN ectodomains dimerize via Cys. Another peptide, with a chain containing Cys linked to a chain containing Cys, Cys, and Cys, was cleaved at Met with cyanogen bromide. Subsequent tandem mass spectrometry established Cys-Cys and Cys-Cys linkages. A glycopeptide with a chain containing Cys linked to a chain containing Cys, Cys, and Cys was treated sequentially with peptide-N-glycosidase F and trypsin. Further treatment of this peptide by one round of manual Edman degradation or tandem mass spectrometry established Cys-Cys and CysCys linkages. These data, establishing the disulfide linkages of all thirteen cysteines of this protein, are consistent with published predictions that the paramyxoviridae HN forms a b-propeller structural fold.