PDBsum entry 4h5i

Protein transport

PDB id: 4h5i

Contents

Protein chains

344 a.a.

Metals

__K ×4

Waters ×428

PDB id:

4h5i

Name:

Protein transport

Title:

Crystal structure of the guanine nucleotide exchange factor sec12 (p1 form)

Structure:

Guanine nucleotide-exchange factor sec12. Chain: a, b. Fragment: unp residues 1-354. Synonym: protein transport protein sec12. Engineered: yes

Source:

Saccharomyces cerevisiae. Yeast. Organism_taxid: 4932. Gene: sec12, sed2, ynr026c, n3244. Expressed in: escherichia coli. Expression_system_taxid: 469008.

Resolution:

1.36Å R-factor: 0.180 R-free: 0.197

Authors:

C.Mcmahon,P.D.Jeffrey,F.M.Hughson

Key ref:

C.McMahon et al. (2012). The structure of Sec12 implicates potassium ion coordination in Sar1 activation. J Biol Chem, 287, 43599-43606. PubMed id: 23109340

Date:

18-Sep-12 Release date: 07-Nov-12

Protein chains

P11655  (SEC12_YEAST) -  Guanine nucleotide-exchange factor SEC12 from Saccharomyces cerevisiae (strain ATCC 204508 / S288c)

Seq: 471 a.a.

Struc: 344 a.a.

J Biol Chem 287:43599-43606 (2012)

PubMed id: 23109340

The structure of Sec12 implicates potassium ion coordination in Sar1 activation.

C.McMahon, S.M.Studer, C.Clendinen, G.P.Dann, P.D.Jeffrey, F.M.Hughson.

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.