Fig. 2: Overview of the specific subunit interactions within the SPOT complex.

In the dimeric (a) and the monomeric (b) complexes, Orm1 interacts with Lcb1 and Lcb2. Lcb1 and Lcb2 interact tightly with each other; while Tsc3 binds exclusively to Lcb2. Color code is the same as in Fig.1. The Lcb1 subunit of the second protomer is shown in darker blue to provide a better view on the dimer interface. The circles indicate the areas of zoom-in views on the specific interactions in panels c-i. c Close-up view on the dimer interface, formed by the interactions between the cytosolic residues of Lcb1 and Lcb2. d, g Close-up views on the interactions between Tsc3 and Lcb2, e Ceramide 44:0;4 binding to Lcb2 and Orm1, i Interactions of the amphipathic helix (AH) of Lcb2 with Orm1, h Orm1 interactions with Lcb1 and Lcb2 via a short α-helix (-C = neg. electrostatic potential), f Ergosterol binding to Lcb1 and Orm1. Residues, which mediate key interactions are shown as sticks. Polar contacts are indicated with yellow dotted lines. The subunits are depicted as cartoons and ligands are shown in ball-and-stick representation. The experimental densities for ceramide and ergosterol are shown in transparent gray.