The structures of Escherichia coli inorganic pyrophosphatase complexed with Ca(2+) or CaPP(i) at atomic resolution
V R Samygina1, A N Popov, E V Rodina
1A.V. Shubnikov Institute of Crystallography, Russian Academy of Sciences, Leninski pr. 59, Moscow, 117333, Russia.
Abstract:
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.
Related Concept Videos
Protein Kinases and Phosphatases
Protein kinases
Many proteins in the cell are regulated by phosphorylation, the addition of a phosphate group. A family of enzymes called kinases...
Allosteric Proteins-ATCase
Aspartate transcarbamoylase (ATCase) is a cytosolic enzyme that catalyzes the condensation of L-aspartate and carbamoyl phosphate to N-carbamoyl-L-aspartate. This reaction is the first step in pyrimidine biosynthesis. UTP and CTP, the end products of the pyrimidine synthesis pathway,...
Diversity of Archaea III
ATP Synthase: Structure
Electron Transport Chain: Complex III and IV
The Replisome
The synthesis of the leading and lagging strands is a highly coordinated process. To explain this, the “Trombone model” was proposed by Bruce Alberts in 1980. The DNA loop formation starts when a primer is synthesized on the parent lagging strand. The loop grows with the...


