=======
The c-ring stoichiometry of ATP synthase is adapted to cell physiological requirements of alkaliphilic Bacillus pseudofirmus OF4
Laura Preiss, Adriana L. Klyszejko, David B. Hicks, Jun Liu, Oliver J. Fackelmayer, Özkan Yildiz, Terry A. Krulwich, and Thomas Meier
PNAS May 7, 2013 110 (19) 7874-7879; doi: 10.1073/pnas.1303333110
Alkaliphilic Bacillus species have evolved several adaptations to cope with the bioenergetic challenge of ATP synthesis at a low pmf . One of these adaptations is the stretch of AxAxAxA instead of GxGxGxG in the c-subunit sequence encoding the inner ring of α-helices of the c-ring. This alteration was proposed to enhance both the c-ring stoichiometry and its size in alkaliphilicBacillus species (19, 20, 26). Our observations here concur with the expectation that a higher c-ring stoichiometry (i.e, increased i ) would be advantageous at a low overall pmf in alkaliphiles (21, 32), because the phosphorylation potential for ATP synthesis (ΔGp) at thermodynamic equilibrium equals i × pmf . The common theme of the enlarged c-ring stoichiometries found in alkaliphilicBacillus species (c13) and the contrasting smaller c10rings found in neutralophilic Bacillus species [e.g., Bacillus PS3 (33), Geobacillus kaustophilus (Fig. S6)] further support this proposed evolutionary adaptation mechanism. The alanine motif is a necessary, but insufficient, adaptation of alkaliphilic Bacillus bacteria. It has a direct influence on the c-ring stoichiometry and its indigenous property to determine the ATP synthase i value, and thus directly modulates the cell’s physiology and bioenergetics, facilitating growth at pH >10. Remarkably, and in agreement with previous work (25), this observation also suggests that i can be adapted by just one or two selected mutations. This property enables adaptation to new environmental challenges, a process that can occur within a rather short evolutionary time frame.
Common Design 