Figure 2

The molecular structure of P. pastoris FAS. (a) Atomic coordinates for the asymmetric unit of P. pastoris FAS, comprising α (light orange) and β (dark orange) subunits, with the density map overlaid. (b) Enlarged view of the asymmetric unit, highlighting different enzymatic domains according to the colour scheme indicated in the domain organisation schematic (below). Grey-coloured regions are non-enzymatic, structural domains. Domain boundaries were assigned based on equivalent domain boundaries from S. cerevisiae FAS. MPT—malonyl/palmitoyl transferase, ACP—acyl carrier protein, KR—ketoacyl reductase, KS—ketoacyl synthase, PPT—phosphopantetheine transferase, AT—acetyl transferase, ER—enoyl reductase, DH—dehydratase. (c) Clipped view of the sharpened FAS density map, coloured according to radius. The box highlights the region of the reaction chamber selected for the first focussed 3D classification. (d) Enlarged image of the region depicted by the box in (c) (upper) compared with the sharpened, asymmetric reconstruction of FAS derived from an ACP density-containing class from the first focussed 3D classification (lower). Further details (including all classes) from the first focussed classification are given in Supplementary Fig S2a-c. (e) Atomic coordinates for the ACP domain of FAS fitted into ACP density from the map shown in (d, bottom). ACP is also shown in the context of the full FAS complex. (f) Representative classes from the second focussed 3D classification (with expanded masked region) of the complex interior. Atomic coordinates for ACP are shown fitted into the three classes containing putative ACP density to give an indication of size. One class shows no putative density for ACP (lower right). All maps are shown at the same contour level. All classes from the second focussed classification are given in Supplementary Fig S2d. (g) Density map of FAS shown at a low contour level (i.e., including weak density), coloured according to subunit (α—light orange, β—dark orange). Low-resolution density corresponding to the flexible dimerization module 2 (DM2) element is highlighted in red.