Purification of the Porcine rubulavirus attachment protein by liquid isoelectric focusing

Porcine rubulavirus (PoRV) is an emerging virus responsible for meningoencephalitis, respiratory distress, and reproductive alterations in pigs. The hemagglutinin-neuraminidase (HN) glycoprotein is the most exposed and antigenic of the virus proteins. HN plays central roles in PoRV infection; i.e., it recognizes sialic acid-containing cell receptors that mediate virus attachment and penetration; in addition, its neuraminidase (sialic acid hydrolysis) activity has been proposed to be a virulence factor. So, HN is an ideal target for therapeutic treatment and prevention of this viral infection. This work describes a simple, fast, and sensitive method to purify the active form of HN protein based on its isoelectric point. HN was purified at a pH of 4.4, at which a single protein band of 66 kDa was observed on SDS-PAGE. Pure HN showed a maximal enzymatic activity at pH 3.5 and 37 degrees C using bovine fetuin as substrate. However, it retains circa 80% of its activity at a wide temperature range from 30 to 55 degrees C. We also describe improvements of neuraminidase determination method, which permits analysis in a microplate spectrophotometer, thereby increasing the sensitivity and reducing the costs of valuable reagents and biological samples.

Structural disorder and modular organization in Paramyxovirinae N and P

The existence and extent of disorder within the replicative complex (N, P and the polymerase, L) of Paramyxovirinae were investigated, drawing on the discovery that the N-terminal moiety of the phosphoprotein (P) and the C-terminal moiety of the nucleoprotein (N) of measles virus are intrinsically unstructured. We show that intrinsic disorder is a widespread property within Paramyxovirinae N and P, using a combination of different computational approaches relying on different physico-chemical concepts. Notably, experimental support that has often gone unnoticed for most of the predictions has been found in the literature. Identification of disordered regions allows the unveiling of a common organization in all Paramyxovirinae P, which are composed of six modules defined on the basis of structure or sequence conservation. The possible functional significance of intrinsic disorder is discussed in the light of experimental data, which show that unstructured regions of P and N are involved in numerous interactions with several protein and protein-RNA partners. This study provides a contribution to the rather poorly investigated field of intrinsically disordered proteins and helps in targeting protein domains for structural studies.

Purification and characterization of the hemagglutinin-neuraminidase of Porcine rubulavirus LPMV

The Hemagglutinin-Neuraminidase (HN) from the LPMV strain of Porcine rubulavirus was purified from virions by ultracentrifugation in a continuous 20-60% sucrose gradient and by ion exchange chromatography. The HN is a glycoprotein of 66 kDa constituted by 50.5, 13.3 and 13.6% of non polar, uncharged polar, and charged polar amino acids, respectively. The HN contains 4% of carbohydrates, its glycannic portion is constituted by Man, Gal, GlcNAc, GalNAc, and Neu5Ac in 3:3:4:1:1 molar ratios. The HN possesses hemagglutinating activity in the presence of erythrocytes from several animal species, including human ABO, and treating the erythrocytes with neuraminidase or pronase abolishes this activity. The binding specificity of the purified HN was determined by hapten inhibition assays, indicating that the hemagglutinating activity of the HN is specific for sialic acid and Neu5Acalpha2,3Gal-containing structures.

Secondary structure prediction of the hemagglutinin-neuraminidase from a porcine rubulavirus

The Hemagglutinin-Neuraminidase (HN) from 'La Piedad, Michoacan' porcine rubulavirus (LPMV) interacts specifically with NeuAc alpha 2,3 lactose residues on the target cell. In this work we report the secondary structure of this protein, determined with five different theoretical algorithms. Results indicate that the HN protein is organized in: an intracellular region (from amino acid 1 to 25); in a beta-strand transmembrane region (residue 26 to 47), typically hydrophobic, rigid and solvent inaccessible; and extracellular region (48 to 576), which possesses hemagglutinating and neuraminidase activity. The secondary structure in this region is organized in a beta-loop-beta alternated with few alpha-helices. Regions with structural and functional implications were determined by pattern search and multiple alignment of the HN from LPM with 12 rubulaviruses and paramyxoviruses HN sequences. The low diversity observed among the HN sequences evaluated indicates that in general the structural organization of the protein, and in particular its sugar binding domain, is closely related among both genera, thus suggesting that the sugar binding domain is well preserved through evolution.