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Folding and stability of the b subunit of the F 1 F 0 ATP synthase
Author(s) -
Revington Matthew,
Dunn Stanley D.,
Shaw Gary S.
Publication year - 2002
Publication title -
protein science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.353
H-Index - 175
eISSN - 1469-896X
pISSN - 0961-8368
DOI - 10.1110/ps.3200102
Subject(s) - atp synthase , dimer , atp synthase gamma subunit , chemistry , protein subunit , crystallography , protein folding , circular dichroism , denaturation (fissile materials) , atp hydrolysis , folding (dsp implementation) , equilibrium unfolding , stereochemistry , enzyme , atpase , biochemistry , nuclear chemistry , organic chemistry , electrical engineering , gene , engineering
The F 1 F 0 ATP synthase is a reversible molecular motor that employs a rotary catalytic cycle to couple a chemiosmotic membrane potential to the formation/hydrolysis of ATP. The multisubunit enzyme contains two copies of the b subunit that form a homodimer as part of a narrow, peripheral stalk structure that connects the membrane (F 0 ) and soluble (F 1 ) sectors. The three‐dimensional structure of the b subunit is unknown making the nature of any interactions or conformational changes within the F 1 F 0 complex difficult to interpret. We have used circular dichroism and analytical ultracentrifugation analyses of a series of N‐ and C‐terminal truncated b proteins to investigate its stability and structure. Thermal denaturation of the b constructs exhibited distinct two‐state, cooperative unfolding with T m values between 30 and 40°C. CD spectra for the region comprising residues 53–122 ( b 53–122 ) showed θ 222 /θ 208 = 0.99, which reduced to 0.92 in the presence of the hydrophobic solvent trifluoroethanol. Thermodynamic parameters for b 53–122 (ΔG, ΔH and ΔC p ) were similar to those reported for several nonideal, coiled‐coil proteins. Together these results are most consistent with a noncanonical and unstable parallel coiled‐coil at the interface of the b dimer.