Modulation of Nucleotide Specificity of Thermophilic FoF1-ATP Synthase by epsilon-Subunitстатья
Статья опубликована в высокорейтинговом журнале
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Дата последнего поиска статьи во внешних источниках: 18 июля 2013 г.
Аннотация:The C-terminal two alpha-helices of the epsilon-subunit of thermophilic Bacillus FoF1-ATP synthase (TFoF1) adopt two conformations: an extended long arm ("up-state") and a retracted hairpin ("down-state"). As ATP becomes poor, changes the conformation from the down-state to the up-state and suppresses further ATP hydrolysis. Using TFoF1 expressed in Escherichia coli, we compared TFoF1 with up-and down-state epsilon in the NTP (ATP, GTP, UTP, and CTP) synthesis reactions. TFoF1 with the up-state epsilon was achieved by inclusion of hexokinase in the assay and TFoF1 with the down-state epsilon was represented by epsilon Delta c-TFoF1, in which epsilon lacks C-terminal helices and hence cannot adopt the up-state under any conditions. The results indicate that TFoF1 with the down-state epsilon synthesizes GTP at the same rate of ATP, whereas TFoF1 with the up-state epsilon synthesizes GTP at a half-rate. Though rates are slow, TFoF1 with the down-state epsilon even catalyzes UTP and CTP synthesis. Authentic TFoF1 from Bacillus cells also synthesizes ATP and GTP at the same rate in the presence of adenosine 5’-(beta,gamma-imino) triphosphate (AMP-PNP), an ATP analogue that has been known to stabilize the downstate. NTP hydrolysis and NTP-driven proton pumping activity of epsilon Delta c-TFoF1 suggests similar modulation of nucleotide specificity in NTP hydrolysis. Thus, depending on its conformation, epsilon-subunit modulates substrate specificity of TFoF1.