Structural study of H+-translocating inorganic pyrophosphatase

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Proton-translocating inorganic pyrophosphatase is a membrane protein that uses the energy from the hydrolysis of inorganic pyrophosphate to transport protons across biological membranes. This study used X-ray crystallography to determine the structure of this enzyme without boundpyrophosphate. The enzyme was purified from the plant vacuolar membrane and crystallized in the absence of pyrophosphate. Crystals were grown in a complex with an antibody fragment that specifically binds to the enzyme in the absence of bound pyrophosphate. The initial crystals showed a diffraction resolution of 4.1 angstrom. This resolution limit was improved to 3.2 angstrom by optimizing the conditions ofcrystallization and cryoprotection.