Figure 4

The KLH2 tridecamer at 30-Å resolution. (a) Side view and (a') top view of the 3D reconstruction at 30-Å resolution as obtained from negatively stained EM images. Segmentation was based on the fitting of the published molecular model of KLH1 [2]. Fenestration and right-handed helical appearance of the cylinder wall results from the oblique arrangement of subunit dimers (purple). Note that this helix is steadily continued in the additional (the upper) decamer. (b, b') The same situation as in a, a', but with most of the cylinder wall transparent to reveal the collar complexes (golden). (c, c') Three copies of the molecular model of the KLH1 decamer (for the latter, see [2]) fitted into the 30-Å structure, and shown with the collar complexes and three consecutive subunit dimers as extracted from the 30-Å structure. Note that the 3D volume is somewhat larger than the molecular model; this is due to the negative staining and flattening of the particles used for 3D reconstruction. (d, d') Three consecutive subunit dimers of the fitted molecular model (ribbon style). This helical association mode is also continued in the larger multidecamers. Formally, the turn between the didecamer and the attached decamer is 36°, but it is actually 3 × 36° = 108° if topologically identical positions are compared.