A pseudoatomic model of the COPII cage obtained from cryo-electron microscopy and mass spectrometry

• DOI: 10.1038/nsmb.2467
• Publication Date: 2012-12-21T10:57:06Z
• Authors: Alex J Noble; Qian Zhang; Jason O'Donnell; Hanaa Hariri; Nilakshee Bhattac...; Alan G Marshall; Scott M Stagg
• Keywords: COPII; Tethering; COPI; Cage; Vesicular Transport Proteins

COPII vesicles transport proteins from the endoplasmic reticulum to the Golgi apparatus. Previous COPII-cage cryo-EM structures lacked the resolution necessary to determine the residues of Sec13 and Sec31 that mediate assembly and flexibility of the COPII cage. Here we present a 12-Å structure of the human COPII cage, where the tertiary structure of Sec13 and Sec31 is clearly identifiable. We employ this structure and a homology model of the Sec13-Sec31 complex to create a reliable pseudoatomic model of the COPII cage. We combined this model with hydrogen/deuterium-exchange MS analysis to characterize four distinct contact regions at the vertices of the COPII cage. Furthermore, we found that the two-fold symmetry of the Sec31 dimeric region in Sec13-Sec31 is broken upon cage formation and that the resulting hinge is essential to form the proper edge geometry in COPII cages.