The exocyst is a conserved protein complex essential for trafficking secretory vesicles to the plasma membrane. The structure of the C-terminal domain of the exocyst subunit Sec6p reveals multiple helical bundles, which are structurally and topologically similar to Exo70p and the C-terminal domains of Exo84p and Sec15, despite <10% sequence identity. The helical bundles appear to be evolutionarily related molecular scaffolds that have diverged to create functionally distinct exocyst proteins.