title: Inorganic pyrophosphatases: one substrate, three mechanisms.
abstract: Soluble inorganic pyrophosphatases (PPases) catalyse an essential reaction, the hydrolysis of pyrophosphate to inorganic phosphate. In addition, an evolutionarily ancient family of membrane-integral pyrophosphatases couple this hydrolysis to Na(+) and/or H(+) pumping, and so recycle some of the free energy from the pyrophosphate. The structures of the H(+)-pumping mung bean PPase and the Na(+)-pumping Thermotoga maritima PPase solved last year revealed an entirely novel membrane protein containing 16 transmembrane helices. The hydrolytic centre, well above the membrane, is linked by a charged "coupling funnel" to the ionic gate about 20Å away. By comparing the active sites, fluoride inhibition data and the various models for ion transport, we conclude that membrane-integral PPases probably use binding of pyrophosphate to drive pumping.
authors.affiliation: Institute of Biotechnology, University of Helsinki, Helsinki, Finland. tommi.kajander@helsinki.fi
authors.forename: Tommi
authors.initials: T
authors.lastname: Kajander
authors.forename: Juho
authors.initials: J
authors.lastname: Kellosalo
authors.forename: Adrian
authors.initials: A
authors.lastname: Goldman
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000737:chemistry; D020134:Catalytic Domain; D011756:Diphosphates / Q000737:chemistry*; D006801:Humans; D006860:Hydrogen Bonding; D006868:Hydrolysis; D008958:Models, Molecular; D017433:Protein Structure, Secondary; D011755:Pyrophosphatases / Q000737:chemistry*
chemical_list: D001426:Bacterial Proteins; D011756:Diphosphates; C107241:diphosphoric acid; D011755:Pyrophosphatases