1I40: Structure Of Inorganic Pyrophosphatase

Two structures of Escherichia coli soluble inorganic pyrophosphatase (EPPase) complexed with calcium pyrophosphate (CaPP(i)-EPPase) and with Ca(2+) (Ca(2+)-EPPase) have been solved at 1.2 and 1.1 A resolution, respectively. In the presence of Mg(2+), this enzyme cleaves pyrophosphate (PP(i)) into two molecules of orthophosphate (P(i)). This work has enabled us to locate PP(i) in the active site of the inorganic pyrophosphatases family in the presence of Ca(2+), which is an inhibitor of EPPase.Upon PP(i) binding, two Ca(2+) at M1 and M2 subsites move closer together and one of the liganded water molecules becomes bridging. The mutual location of PP(i) and the bridging water molecule in the presence of inhibitor cation is catalytically incompetent. To make a favourable PP(i) attack by this water molecule, modelling of a possible hydrolysable conformation of PP(i) in the CaPP(i)-EPPase active site has been performed. The reasons for Ca(2+) being the strong PPase inhibitor and the role in catalysis of each of four metal ions are the mechanistic aspects discussed on the basis of the structures described.
PDB ID: 1I40Download
MMDB ID: 18098
PDB Deposition Date: 2001/2/19
Updated in MMDB: 2001/12
Experimental Method:
x-ray diffraction
Resolution: 1.1  Å
Source Organism:
Similar Structures:
Biological Unit for 1I40: hexameric; determined by author and by software (PISA,PQS)
Molecular Components in 1I40
Label Count Molecule
Proteins (6 molecules)
Inorganic Pyrophosphatase(Gene symbol: ppa)
Molecule annotation
Chemicals (54 molecules)
* Click molecule labels to explore molecular sequence information.

Citing MMDB