Conformational changes in Sindbis virus induced by decreased pH are revealed by small-angle neutron scattering

Abstract

Alphaviruses, such as Sindbis virus, undergo dramatic changes in three-dimensional structure upon exposure to low pH, and such exposure can establish conditions allowing fusion of the virus membrane with a cell plasma membrane upon return to neutral pH. While exposure to low pH is not required for entry of Sindbis virus into vertebrate or invertebrate cells, the conformational changes occurring at low pH may mimic those occurring upon virus-receptor interaction. Here, we employed small-angle neutron scattering with contrast variation to probe how the structure of a mammalian-grown Sindbis virus responds to moderately acidic pH. Several changes took place throughout the virion structure when the pH decreased from 7.2 to 6.4. Specifically, the RNA in the virion core underwent a conformational change. Additionally, the protein was redistributed. A significant amount of protein moved from the layer containing the lipid bilayer to the exterior of the virion. The results improve our understanding of the pH-driven alteration of Sindbis virus structure.

Fig 1

SANS contrast variation series data for Sindbis virus BHK at pH 7.2. The curves have been offset for clarity. The solid lines are the best fit model intensity profiles determined as described in Materials and Methods. The error bars indicate experimental uncertainties in the data.

Fig 2

SANS contrast variation series data for Sindbis virus BHK at pH 6.4. The curves have been offset for clarity. The high-q data for the two data sets are not shown and were eliminated from the fitting because they were not of sufficient statistical quality. The solid lines are the best fit model intensity profiles determined as described in Materials and Methods. The error bars indicate experimental uncertainties in the data.

Fig 3

Guinier analysis of Sindbis virus BHK at pH 7.2 and 6.4.

Fig 4

Pair distance distribution function for BHK at pH 7.2 (solid line) and 6.4 (dashed line). arb., arbitrary.

Fig 5

Radial-scattering distribution function for BHK at pH 7.2 and 6.4. The shading indicates the radii where the curves are not considered reliable.