Effect of temperature, pH, and metal ion binding on the secondary structure of bacteriorhodopsin: FT-IR study of the melting and premelting transition temperatures
Cd. Heyes et Ma. El-sayed, Effect of temperature, pH, and metal ion binding on the secondary structure of bacteriorhodopsin: FT-IR study of the melting and premelting transition temperatures, BIOCHEM, 40(39), 2001, pp. 11819-11827
We have measured the temperature dependence of the FT-IR spectra of bacteri
orhodopsin (bR) as a function of the pH and of the divalent cation regenera
tion with Ca2+ and Mg2+. It has been found that although the irreversible m
elting transition shows a strong dependence on the pH of the native bR, the
premelting reversible transition at 78-80 degreesC shows very little varia
tion over the pH range studied. It is further shown that the acid blue bR s
hows a red-shifted amide I spectrum at physiological temperature, which sho
ws a more typical alpha -helical frequency component at 1652 cm(-1) and cou
ld be the reason for the observed reduction of its melting temperature and
lack of an observed premelting transition. Furthermore, the thermal transit
ions for Ca2+- and Mg2+-regenerated bR (Ca-bR and Mg-bR, respectively) each
show a premelting transition at the same 78-80 degreesC temperature as the
native purple membrane, but the irreversible melting transition has a slig
ht dependence on the cation identity. The pH dependence of the Ca2+-regener
ated bR is studied, and neither transition varies over the pH range studied
. These results are discussed in terms of the cation contribution to the se
condary structural stability in bR.