Structure-function analysis of two variants of mumps virus hemagglutinin-neuraminidase protein.

A point mutation from guanine (G) to adenine (A) at nucleotide position 1081 in the hemagglutinin-neuraminidase (HN) gene has been associated with neurovirulence of Urabe AM9 mumps virus vaccine. This mutation corresponds to a glutamic acid (E) to lysine (K) change at position 335 in the HN glycoprotein. We have experimentally demonstrated that two variants of Urabe AM9 strain (HN-A1081 and HN-G1081) differ in neurotropism, sialic acidbinding affinity and neuraminidase activity. In the present study, we performed a structure-function analysis of that amino acid substitution; the structures of HN protein of both Urabe AM9 strain variants were predicted. Based on our analysis, the E/K mutation changes the protein surface properties and to a lesser extent their conformations, which in turn reflects in activity changes. Our modeling results suggest that this E/K interchange does not affect the structure of the sialic acid binding motif; however, the electrostatic surface differs drastically due to an exposed short alpha helix. Consequently, this mutation may affect the accessibility of HN to substrates and membrane receptors of the host cells. Our findings appear to explain the observed differences in neurotropism of these vaccine strains.

Structure-function analysis of two variants of mumps virus hemagglutinin-neuraminidase protein

A point mutation from guanine (G) to adenine (A) at nucleotide position 1081 in the hemagglutinin-neuraminidase (HN) gene has been associated with neurovirulence of Urabe AM9 mumps virus vaccine. This mutation corresponds to a glutamic acid (E) to lysine (K) change at position 335 in the HN glycoprotein. We have experimentally demonstrated that two variants of Urabe AM9 strain (HN-A1081 and HN-G1081) differ in neurotropism, sialic acidbinding affinity and neuraminidase activity. In the present study, we performed a structure-function analysis of that amino acid substitution; the structures of HN protein of both Urabe AM9 strain variants were predicted. Based on our analysis, the E/K mutation changes the protein surface properties and to a lesser extent their conformations, which in turn reflects in activity changes. Our modeling results suggest that this E/K interchange does not affect the structure of the sialic acid binding motif; however, the electrostatic surface differs drastically due to an exposed short alpha helix. Consequently, this mutation may affect the accessibility of HN to substrates and membrane receptors of the host cells. Our findings appear to explain the observed differences in neurotropism of these vaccine strains.

Caracterización biológica de tres aislamientos naturales del Rubulavirus porcino (México)

Biological characterization of three natural isolates of the porcine rubulavirus (Mexico). Porcine rubulavirus (PoRV) produces a neurological and reproductive syndrome in pigs called the blue-eye disease, known only from Mexico. Several isolates were grouped by the main symptoms presented during outbreaks: a) neurotropic in piglets, b) broadly neurotropic in piglets and gonadotropic in adults, and c) gonadotropic in adults. We studied some biological properties of three strains, which fall in one of each virus group: La Piedad Michoacán (LPM) and Producción Animal Cerdos 1 (PAC1) and 3 (PAC3), respectively. The analyzed viral properties are mainly related with the trans-membrane hemagglutinin-neuraminidase (HN) and fusion (F) proteins, such as cytopathic effect, hemolysis, hemagglutinating (HA) and neuraminidase (NA) activities. In the infection assays PAC1 strain presented the highest fusogenicity level; however, the most cytolytic strain was PAC3. In addition, HA and NA activities and viral genome of PAC3 strain was detected in supernatants during cell infection earlier than in the other two strains, which shows that PAC3 virions release from the host cell earlier than LPM and PAC1. Experimental determination in purified viruses shows that PAC3 presented a higher HA and NA activities; however, PAC1 shows other interesting properties, such as a high thermostability of HN and differences about substrate profile respect to LPM and PAC3. Our data suggest that NA activity is associated with the virulence of RVP. Rev. Biol. Trop. 56 (2): 487-499. Epub 2008 June 30.

El Rubulavirus porcino causa un síndrome neurológico y reproductivo en cerdos, hasta ahora reportado sólo en México. Los virus aislados se agrupan de acuerdo con los síntomas principales observados durante los brotes en: a) neutrópicos en lechones, b) neurotrópicos en lechones/gonadotrópicos en adultos y c) gonadotrópicos en adultos. En este trabajo se estudiaron tres cepas: La Piedad Michoacán (LPM) y Producción Animal "Cerdos" 1 (PAC1) y 3 (PAC3), ubicadas respectivamente en cada grupo. Las propiedades estudiadas se relacionan principalmente con dos proteínas de la envoltura viral, la hemaglutinina-neuraminidasa (HN) y la proteína de fusión (F). Se cuantificaron el efecto citopático y las actividades de hemólisis, hemaglutinación (HA) y neuraminidasa (NA). En cultivo celular la cepa PAC1 presentó una mayor actividad fusogénica, sin embargo PAC3 presentó la mayor actividad citolítica. La cepa PAC3 fue la primera en ser detectada en sobrenadante de células infectadas (HA, NA y genoma), lo que muestra que sus viriones son liberados al medio antes que las otras dos cepas. PAC3 tuvo las actividades más altas de HA y NA, sin embargo, PAC1 presentó una mayor termoestabilidad en estas actividades de HN y un perfil de substrato algo distinto de los observados para LPM y PAC3. Estos datos sugieren que la actividad de NA está relacionada con la virulencia del RVP.

[Biological characterization of three natural isolates of the porcine rubulavirus (Mexico)]. / Caracterización biológica de tres aislamientos naturales del Rubulavirus porcino (México).

Biological characterization of three natural isolates of the porcine rubulavirus (Mexico). Porcine rubulavirus (PoRV) produces a neurological and reproductive syndrome in pigs called the blue-eye disease, known only from Mexico. Several isolates were grouped by the main symptoms presented during outbreaks: a) neurotropic in piglets, (b) broadly neurotropic in piglets and gonadotropic in adults, and (c) gonadotropic in adults. We studied some biological properties of three strains, which fall in one of each virus group: La Piedad Michoacán (LPM) and Producci6n Animal Cerdos 1 (PAC1) and 3 (PAC3), respectively. The analyzed viral properties are mainly related with the trans-membrane hemagglutinin-neuraminidase (HN) and fusion (F) proteins, such as cytopathic effect, hemolysis, hemagglutinating (HA) and neuraminidase (NA) activities. In the infection assays PAC1 strain presented the highest fusogenicity level; however, the most cytolytic strain was PAC3. In addition, HA and NA activities and viral genome of PAC3 strain was detected in supernatants during cell infection earlier than in the other two strains, which shows that PAC3 virions release from the host cell earlier than LPM and PAC1. Experimental determination in purified viruses shows that PAC3 presented a higher HA and NA activities; however, PAC1 shows other interesting properties, such as a high thermostability of HN and differences about substrate profile respect to LPM and PAC3. Our data suggest that NA activity is associated with the virulence of RVP.