Influenza A viruses use multivalent sialic acid clusters for cell binding and receptor activation
Fig 2
Density-based localization analysis reveals small SA clusters between microvilli.
(A) Spatial distribution of STORM localizations from SNA-A647 on A549 cells showing the coexistence of two structural features, (1) large microvilli as well as (2) small nanodomains. The inset in A shows a pixel image reconstruction (10 nm/pxl) of the localization map in A. (B) Density distribution of localizations shown in A within a search radius of 50 nm. Color scale according to number of neighbor localizations. (C) Final clustering result with identified clusters allows quantification of the cluster area. After all identified clusters were filtered according to their size to selectively analyze non-microvilli structures, we found clusters with an area between 0.005–0.04 μm2 (D). The large cluster labelled by the red dashed line was filtered out (see also S4 Fig). Distribution of the number of molecules per cluster as estimated according to the number of localizations (D, inset). The inner structure of non-microvilli clusters was analyzed according to their local localization density (B). (E) Representative example of two identified clusters showing their inner density gradient. The color code represents the number of nearest neighbor localizations within a radius of 30 nm (i.e. the local localization density). The localization density is plotted on the vertical axis. Distribution of the density difference between background and the cluster center over all identified cluster (F).