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Mutations in a helix-1 motif of the ATP synthase c-subunit of Bacillus pseudofirmus OF4 cause functional deficits and changes in c-ring stability and mobility on SDS-PAGE
The ATP synthase of the alkaliphile Bacillus pseudofirmus OF4 has a tridecameric c- subunit rotor ring. Each c- subunit has an AxAxAxA motif near the center of the inner helix, where neutralophilic bacteria generally have GxGxGxG. Here, we studied the impact of four single and six multiple Ala-to-Gl...
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Published in: | Biochemistry (Easton) 2011-05, Vol.50 (24), p.5497-5506 |
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Main Authors: | , , , , , , |
Format: | Article |
Language: | English |
Online Access: | Get full text |
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Summary: | The ATP synthase of the alkaliphile
Bacillus pseudofirmus
OF4 has a tridecameric
c-
subunit rotor ring. Each
c-
subunit has an AxAxAxA motif near the center of the inner helix, where neutralophilic bacteria generally have GxGxGxG. Here, we studied the impact of four single and six multiple Ala-to-Gly chromosomal mutations in the A16xAxAxA22 motif on the capacity for non-fermentative growth and, for most of the mutants, on ATP synthesis by ADP + P
i
-loaded membrane vesicles at pH 7.5 and 10.5. SDS-PAGE analyses of the holo-ATP synthases were used to probe stability of the mutant
c-
rotors and mobility properties of the
c-
rotors as well as the monomeric
c-
subunits that are released from them by trichloroacetic acid treatment. Mutants containing an Ala16-to-Gly mutation exhibited the most severe functional defects. On SDS-PAGE, most of the mutant
c-
monomers exhibited increased mobility relative to the WT
c
-subunit, but among the intact
c-
rings, only Ala16-to-Gly containing mutants exhibited significantly increased mobility relative to the WT
c-
ring. The hypothesis that these
c-
rings have a decreased
c-
subunit stoichiometry is still untested but the functional impact of an Ala16-to-Gly mutation clearly depended upon additional Ala-to-Gly mutation(s) and their positions. The double A16/20G mutant exhibited a larger functional deficit than both the A16G and A16/18G mutants. Most of the mutant
c-
rings showed
in vitro
instability relative to wild-type (WT)
c
-ring. However, the functional deficits of mutants did not correlate well with the extent of
c-
ring stability loss, so this property is unlikely to be a major factor
in vivo
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ISSN: | 0006-2960 1520-4995 |
DOI: | 10.1021/bi2005009 |