4H5J image
Entry Detail
PDB ID:
4H5J
Title:
Crystal Structure of the Guanine Nucleotide Exchange Factor Sec12 (P64 form)
Biological Source:
Source Organism:
Host Organism:
PDB Version:
Deposition Date:
2012-09-18
Release Date:
2012-11-07
Method Details:
Experimental Method:
Resolution:
2.60 Å
R-Value Free:
0.21
R-Value Work:
0.17
R-Value Observed:
0.18
Space Group:
P 64
Macromolecular Entities
Polymer Type:polypeptide(L)
Description:Guanine nucleotide-exchange factor SEC12
Chain IDs:A, B
Chain Length:365
Number of Molecules:2
Biological Source:Saccharomyces cerevisiae
Modified Residue
Compound ID Chain ID Parent Comp ID Details 2D Image
MSE A MET SELENOMETHIONINE
Primary Citation
The structure of sec12 implicates potassium ion coordination in sar1 activation.
J.Biol.Chem. 287 43599 43606 (2012)
PMID: 23109340 DOI: 10.1074/jbc.M112.420141

Abstact

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.

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