Protein , folding patterns symmetry

Figure 13.30. Illustration of the four levels of structure in the potassium channel KcsA protein. Left a small section of the protein showing the primary structure, that is, the sequence of aminoacids identified by the side chains, and the secondary structure, that is, the formation of an a-helix. Right the tertiary structure, that is, the formation of larger subunits conisting of several a helices (in this case each subunit consists of three helices), and the quaternary structure, that is, the arrangement of the three-helix subunits in a pattern with four-fold rotational symmetry around a central axis. The a-helix on the left is the longest helix in each of the subunits, which are each shown in slightly different shades. The ion channel that this protein forms is at the center of structure. (Figure provided by P.L. Maragakis based on data from Ref. [232].)...

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