Mating Pheromone Er-11

Mating pheromone Er-11 is a transmembrane signaling protein found in the ciliated protozoan organism Euplotes raikovi. This type of pheromones, or gamones, help to distinguish different classes of cells known as mating types. The gamones help to prepare the cells for conjugation by inducing a cell surface transformation.
All of the E. raikovi pheromones are very similar. Er-11 shares a 56% sequence identity with Er-20. The residues that correspond to the alpha helical arrangments in Er-11 are also similar to those of Er-1, Er-2, and Er-10. Thus, the binding to cell-surface receptors for these pheromones must be a competitive process.
Er-ll is 39 amino acid residues long and consists of 3 alpha helices that are arranged in an up-down-up fashion. In the picture shown above, helix 1 is yellow, helix 2 is purple, and helix 3 is orange. Three disulfide bonds are found in the protein and are colored magenta. They are Cys3-Cys19, Cys10-Cys34, and Cys15-Cys26. Residue 20 is shown in green. This glycine forms a 310 helix. It is the only amino acid to take part in this formation however. 

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