The enzymes exopolyphosphatase/guanosine pentaphosphate phosphohydrolase (PPX/GppA) play important roles in the bacterial stringent response. PPX degrades inorganic polyphosphate (polyP), a polymer composed of a few to hundreds of phosphate residues supporting cell survival in the stationary phase. The crystal structure of PPX from Porphyromonas gingivalis (PgPPX) in complex with catalytic magnesium ions and several sulfate ions was solved. PgPPX contained two domains and represented a “closed” configuration. Four sulfate ions forming a linear dispersed chain were observed in the aqueduct of the PPX dimer, which the long polyP chain most likely occupied. The side chain of R255 stretched into the cavity where polyP could be located, obstructing the entrance of larger substrates such as NTP and NDP. This study provided the first view into the structure of the PPX/GppA homolog in complex with magnesium ions and substrate analogs and explained how PgPPX implemented its functionality.

外多磷酸酶/五磷酸鸟苷磷酸水解酶 (PPX/GppA) 在细菌严格反应中起重要作用。PPX 可降解无机多磷酸盐 (polyP)，这是一种由数至数百个磷酸盐残基组成的聚合物，可支持细胞在静止期存活。解决了牙龈卟啉单胞菌( Pg PPX) 与催化镁离子和几种硫酸根离子络合的 PPX 晶体结构。PGPPX 包含两个域并代表“封闭”配置。在 PPX 二聚体的导水管中观察到四个硫酸根离子形成线性分散链，其中长 polyP 链最有可能占据。R255 的侧链延伸到 polyP 所在的空腔中，阻碍了较大的底物如 NTP 和 NDP 的进入。这项研究提供了与镁离子和底物类似物复合的 PPX/GppA 同系物结构的第一个观点，并解释了Pg PPX 如何实现其功能。