Mild proteolysis induces a ready-to-fuse state on Sendai virus envelope

The Sendai virus fuses with host cell membranes in a pH-independent manner through an unknown mechanism. Here we report that mild trypsin pre-treatments of Sendai virions, for example 15 min at 4 degrees C, give Sendai virions the ability to fuse at a rate up to 10-fold higher than control. By using human erythrocytes as host cell membranes, viral fusion was assessed by hemolysis as well as fluorescence dequenching of octadecyl rhodamine B chloride. The mild protease treatment strikingly shortens the lag time taken by the virus to start the fusion process. Similar data were obtained on reconstituted Sendai virus envelope. Among proteases, tested as fusion enhancer, trypsin is more effective than either endoproteinase Lys-C, chymotrypsin, or endoproteinase Arg-C. After removal of trypsin from treated virions the fusion rate enhancement remains for hours at room temperature. The lack of protease specificity, together with the impossibility to detect any new N-terminal products, suggests that only a small percentage of viral envelope components are cleaved, still a large enough number to set the envelope in a ready-to-fuse state

Selective extraction of haemagglutinin and matrix protein from Sendai virions by employing trifluoperazine as a detergent

Incubation of trifluoperazine, a local anaesthetic, at concentrations higher than the cmc with Sendai virus particles produces the selective solubilization of the haemagglutinin neuraminidase (HN) and matrix (M) proteins. This phenomenon involves aggregation of the Sendai virions and therefore the separation of HN and M from the rest of the particle can be performed by bench centrifugation. The supernatant contains the HN and M proteins and HN, once inserted into liposomes, elicits its own biological activities. Therefore, the method seems suitable for purifying large amounts of HN

Mild proteolysis induces a ready-to-fuse state on Sendai virus envelope

The Sendai virus fuses with host cell membranes in a pH-independent manner through an unknown mechanism. Here we report that mild trypsin pre-treatments of Sendai virions, for example 15 min at 4 degrees C, give Sendai virions the ability to fuse at a rate up to 10-fold higher than control. By using human erythrocytes as host cell membranes, viral fusion was assessed by hemolysis as well as fluorescence dequenching of octadecyl rhodamine B chloride. The mild protease treatment strikingly shortens the lag time taken by the virus to start the fusion process. Similar data were obtained on reconstituted Sendai virus envelope. Among proteases, tested as fusion enhancer, trypsin is more effective than either endoproteinase Lys-C, chymotrypsin, or endoproteinase Arg-C. After removal of trypsin from treated virions the fusion rate enhancement remains for hours at room temperature. The lack of protease specificity, together with the impossibility to detect any new N-terminal products, suggests that only a small percentage of viral envelope components are cleaved, still a large enough number to set the envelope in a ready-to-fuse state

Geomorphological and Geoarchaeological Evidence of the Medieval Deluge in the Tagliamento River (NE Italy)

Between the second part of the sixth century and the seventh century, many regions of Europe have been characterized by dramatic changes in the hydrographic setting, probably related to a strong cooling phase. In northern Italy, the chronicle of a huge flood event referred by the Lombard historian Paul the Deacon to the autumn of 589 AD has achieved a major importance and induced many researchers to attribute to this \u201cdeluge\u201d episode many of the floods occurred during early Middle Age. In this paper, we consider the alluvial system of Tagliamento, which is one of the main rivers fed by south-eastern Alps and experienced a strong avulsion phase between the sixth and eleventh centuries. In that period, the river activated up to three branches and the hydrographical changes strongly influenced the human activity. This work critically reanalyses both published data and new stratigraphic and archaeologic evidence in order to assess and quantify the times and modes of this instability phase. The data suggest the occurrence of an extreme flood event at the end of the sixth century, which was also responsible for the burial of the ancient city of Concordia Sagittaria. The geochronological constraints suggest the possibility that this catastrophic episode occurred in 589 AD, thus confirming the Medieval Chronicle. Anyhow, other alluvial events occurred in the distal plain of Tagliamento River slightly before and after that moment