TY - JOUR
T1 - Hydration-state change of horse heart cytochrome c corresponding to trifluoroacetic-acid-induced unfolding
AU - Miyashita, Yusuke
AU - Wazawa, Tetsuichi
AU - Mogami, George
AU - Takahashi, Satoshi
AU - Sambongi, Yoshihiro
AU - Suzuki, Makoto
N1 - Funding Information:
This work was supported by grants from the Ministry of Education, Culture, Sports, Science, and Technology of Japan (Grant-in-Aid for Scientific Research on Innovative Areas: 20118001, 20118005, and 20118008) and from CREST/JST.
PY - 2013/1/8
Y1 - 2013/1/8
N2 - We investigate the hydration state of horse-heart cytochrome c (hh cyt c) in the unfolding process induced by trifluoroacetic acid (TFA). The conformation of hh cyt c changes from the native (N) state (2.9< pH< 6.0) to the acid-unfolded (UA) state (1.7< pH< 2.0) to the acid-induced molten globule (A) state (pH ∼1.2). Hydration properties of hh cyt c during this process are measured at 20°C by high-resolution dielectric relaxation (DR) spectroscopy, UV-vis absorbance, and circular dichroism spectroscopy. Constrained water of hh cyt c is observed at every pH as an ∼5-GHz Debye component (DC) (DR time, τD ∼30 ps) and its DR amplitude (DRA) is increased by 77% upon N-to-UA transition, when pH changes from 6.0 to 2.0. Even in the N state, the DRA of the constrained-water component is found to be increased by 22% with decreasing pH from 6.0 to 2.9, suggesting an increase in the accessible surface area of native hh cyt c. Moreover, hypermobile water around native hh cyt c is detected at pH 6.0 as a 19-GHz DC (τD ∼ 8.4 ps< τDW = 9.4 ps), but is not found at other pH values. The DRA signal of constrained water is found to return to the pH 2.9 (N-state) level upon UA-to-A transition. Fast-response water (slightly slower than bulk) around A-state hh cyt c is detected at pH 1.2, and this suggests some accumulation of TFA- ions around the peptide chain. Thus, this high-resolution DR spectroscopy study reveals that hh cyt c exhibits significant hydration-state change in the TFA-unfolding process.
AB - We investigate the hydration state of horse-heart cytochrome c (hh cyt c) in the unfolding process induced by trifluoroacetic acid (TFA). The conformation of hh cyt c changes from the native (N) state (2.9< pH< 6.0) to the acid-unfolded (UA) state (1.7< pH< 2.0) to the acid-induced molten globule (A) state (pH ∼1.2). Hydration properties of hh cyt c during this process are measured at 20°C by high-resolution dielectric relaxation (DR) spectroscopy, UV-vis absorbance, and circular dichroism spectroscopy. Constrained water of hh cyt c is observed at every pH as an ∼5-GHz Debye component (DC) (DR time, τD ∼30 ps) and its DR amplitude (DRA) is increased by 77% upon N-to-UA transition, when pH changes from 6.0 to 2.0. Even in the N state, the DRA of the constrained-water component is found to be increased by 22% with decreasing pH from 6.0 to 2.9, suggesting an increase in the accessible surface area of native hh cyt c. Moreover, hypermobile water around native hh cyt c is detected at pH 6.0 as a 19-GHz DC (τD ∼ 8.4 ps< τDW = 9.4 ps), but is not found at other pH values. The DRA signal of constrained water is found to return to the pH 2.9 (N-state) level upon UA-to-A transition. Fast-response water (slightly slower than bulk) around A-state hh cyt c is detected at pH 1.2, and this suggests some accumulation of TFA- ions around the peptide chain. Thus, this high-resolution DR spectroscopy study reveals that hh cyt c exhibits significant hydration-state change in the TFA-unfolding process.
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U2 - 10.1016/j.bpj.2012.11.3825
DO - 10.1016/j.bpj.2012.11.3825
M3 - Article
C2 - 23332069
AN - SCOPUS:84872160331
SN - 0006-3495
VL - 104
SP - 163
EP - 172
JO - Biophysical Journal
JF - Biophysical Journal
IS - 1
ER -