Yh. Chi et al., Thermodynamic characterization of the human acidic fibroblast growth factor: Evidence for cold denaturation, BIOCHEM, 40(25), 2001, pp. 7746-7753
The thermodynamic parameters characterizing the conformational stability of
the human acidic fibroblast growth factor (hFGF-1) have been determined by
isothermal urea denaturation and thermal denaturation at fixed concentrati
ons of urea using fluorescence and far-UV CD circular dichroism (CD) spectr
oscopy. The equilibrium unfolding transitions at pH 7.0 are adequately desc
ribed by a two-state (native tt unfolded state) mechanism. The stability of
the protein is pH-dependent, and the protein unfolds completely below pH 3
.0 Cat 25 degreesC). hFGF-1 is shown to undergo a two-state transition only
in a narrow pH range (pH 7.0-8.0). Under acidic (pH <6.0) and basic (pH >
8.0) conditions, hFGF-1 is found to unfold noncooperatively, involving the
accumulation of intermediates. The average temperature of maximum stability
is determined to be 295.2 K. The heat capacity change (DeltaC(p)) for the
unfolding of hFGF-1 is estimated to be 2.1 +/- 0.5 kcal mol(-1) K-1. Temper
ature denaturation experiments in the absence and presence of urea show tha
t hFGF-1 has a tendency to undergo cold denaturation. Two-dimensional H-1-N
-15 HSQC spectra of hFGF-1 acquired at subzero temperatures clearly show th
at hFGF-1 unfolds under low-temperature conditions. The significance of the
noncooperative unfolding under acidic conditions and the cold denaturation
process observed in hFGF-1 are discussed in detail.