4KDC: Crystal Structure of UBIG

UbiG and Coq3 (orthologue in eukaryotes) are SAM-MTases (S-adenosylmethionine-dependent methyltransferases) that catalyse both O-methylation steps in CoQ biosynthesis from prokaryotes to eukaryotes. However, the detailed molecular mechanism by which they function remains elusive. In the present paper, we report that UbiG/Coq3 defines a novel class of membrane-binding proteins. Escherichia coli UbiG binds specifically to liposomes containing PG (phosphatidylglycerol) or CL (cardiolipin, or diphosphatidylglycerol), two major lipid components of the E. coli plasma membrane, whereas human and yeast Coq3 display a strong preference for liposomes enriched with CL, a signature lipid of the mitochondrial membrane. The crystal structure of UbiG from E. coli was determined at 2.1 A (1 A = 0.1 nm) resolution. The structure exhibits a typical Class I SAM-MTase fold with several variations, including a unique insertion between strand beta5 and helix alpha10. This insertion is highly conserved and is required for membrane binding. Mutation of the key residues renders UbiG unable to efficiently bind liposome in vitro and the mutant fails to rescue the phenotype of DeltaubiG strain in vivo. Taken together, our results shed light on a novel biochemical function of the UbiG/Coq3 protein.
PDB ID: 4KDCDownload
MMDB ID: 119711
PDB Deposition Date: 2013/4/24
Updated in MMDB: 2014/05
Experimental Method:
x-ray diffraction
Resolution: 2.09  Å
Source Organism:
Similar Structures:
Biological Unit for 4KDC: monomeric; determined by author and by software (PISA)
Molecular Components in 4KDC
Label Count Molecule
Protein (1 molecule)
3-demethylubiquinone-9 3-methyltransferase(Gene symbol: ubiG)
Molecule annotation
* Click molecule labels to explore molecular sequence information.

Citing MMDB