Figure 4
Predicted secondary structure elements in VDAC from the crown groups of plants, animals, and fungi. Predictions were made as described in Methods. For each summary diagram, the putative N-terminal α-helix is indicated by a hatched bar labelled "N" on the left, subsequent β-strands are indicated by filled rectangles, and the intervening loops are shown as thin lines. According to the model in Fig. 1, the N-terminal helix resides in the intermembrane space, and the subsequent loops and turns alternate between exposure to the cytosol and to the intermembrane space. β-strands with weak support are indicated in grey. The lower panel shows the model for Neurospora crassa VDAC structure derived in [16]. Structural elements are as described for the plant, animal and fungal models, except that the checkerboard region indicates a C-terminal segment that is exposed to the cytosol rather than forming the 19thβ-strand (see text for discussion). Below the model of N. crassa VDAC structure, rectangles indicate segments, that when absent in porin variants, create molecules that form pores of wild-type conductivity (open), or inefficiently form pores that are either unstable or of reduced conductivity (filled) in artificial membranes. The position of the GLK sequence and the eukaryotic porin signature motif (PS00558) are also noted. Vertical lines connect regions of homology and the curved arrow indicates the discrepancy for the placement of β8 between previous models (see [4]) and the current predictions.