4H5J

Crystal Structure of the Guanine Nucleotide Exchange Factor Sec12 (P64 form)

Summary for 4H5J

• Entry DOI: 10.2210/pdb4h5j/pdb
• Related: 4H5I
• Descriptor: Guanine nucleotide-exchange factor SEC12, POTASSIUM ION (3 entities in total)
• Functional Keywords: copii vesicle budding, potassium binding site, beta propeller, protein transport
• Biological source: Saccharomyces cerevisiae (yeast)
• Cellular location: Endoplasmic reticulum membrane; Single-pass type II membrane protein: P11655
• Total number of polymer chains: 2
• Total formula weight: 80693.75

Authors

McMahon, C.,Jeffrey, P.D.,Hughson, F.M. (deposition date: 2012-09-18, release date: 2012-11-07, Last modification date: 2024-11-20)

Primary citation

McMahon, C.,Studer, S.M.,Clendinen, C.,Dann, G.P.,Jeffrey, P.D.,Hughson, F.M.
The structure of sec12 implicates potassium ion coordination in sar1 activation.
J.Biol.Chem., 287:43599-43606, 2012

PubMed Abstract: Coat protein II (COPII)-coated vesicles transport proteins and lipids from the endoplasmic reticulum to the Golgi. Crucial for the initiation of COPII coat assembly is Sec12, a guanine nucleotide exchange factor responsible for activating the small G protein Sar1. Once activated, Sar1/GTP binds to endoplasmic reticulum membranes and recruits COPII coat components (Sec23/24 and Sec13/31). Here, we report the 1.36 Å resolution crystal structure of the catalytically active, 38-kDa cytoplasmic portion of Saccharomyces cerevisiae Sec12. Sec12 adopts a β propeller fold. Conserved residues cluster around a loop we term the "K loop," which extends from the N-terminal propeller blade. Structure-guided site-directed mutagenesis, in conjunction with in vitro and in vivo functional studies, reveals that this region of Sec12 is catalytically essential, presumably because it makes direct contact with Sar1. Strikingly, the crystal structure also reveals that a single potassium ion stabilizes the K loop; bound potassium is, moreover, essential for optimum guanine nucleotide exchange activity in vitro. Thus, our results reveal a novel role for a potassium-stabilized loop in catalyzing guanine nucleotide exchange.

PubMed: 23109340
DOI: 10.1074/jbc.M112.420141

Experimental method

X-RAY DIFFRACTION (2.601 Å)