Crystal structure of a membrane-embedded H⁺-translocating pyrophosphatase

S.M. Lin, et al. Nature. 484, 399-404 (2012)

Speaker: Chin-Kun Tsai (蔡進焜)                                         Time: 13:00~14:00, Oct.31, 2012

Commentator: Prof. Woei-Jer Chuang (莊偉哲教授)          Place: Room 601

Abstract

H⁺-translocating pyrophosphatases (H⁺-PPases) is an electrogenic proton pump that acidifies vacuoles via active proton transport across vacuolar membrane¹ and utilizes metabolic by-product, cytosolic PPi, as energy sources for proton translocation². H⁺-PPases were identified ashomodimers from the membranes of prokaryotes, protozoa and plants³. However, the structural mechanism of how the proton pumping and PPi hydrolysis through H⁺-PPases are not clear. The authors solved the crystal structure of the Vigna radiata H⁺-PPase (VrH⁺-PPase) bound toimidodiphosphate (IDP) at 2.35 Å resolution as the first step to reveal the mechanism of proton translocation in the vacuoles of plant cells. Each VrH⁺-PPase protein is folded with 16 transmembrane (TM) helices. Ten of these TM helices constitute the outer walls and maintain the structural stability of protein. The other six TM helices bundle together to form a potential proton translocation pathway. This pathway consists of numerous charged residues and five Mg²⁺ ions for IDP binding and proton pumping. H⁺-PPases hydrolyze PPi to provide energy, and then convey proton from active site to the vacuolar lumen. Moreover, the vacuolar portion of H⁺-PPase consists of hydrophobic residues forms a hydrophobic gate to maintain proton unidirectional translocation. The combination of structure and biochemical data provide a working model for the coupling of PPi hydrolysis and proton pumping by the H⁺-PPases.

References

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