A differential scanning calorimetric study of the thermal unfolding of apo- and holo-cytochrome b562.
Cytochrome b562 is a four-helix-bundle protein containing a non-covalently bound b-type heme prosthetic group. In the absence of heme, cytochrome b562 remains highly structured under native conditions. Here we report thermodynamic data for the thermal denaturation of the holo- and apoproteins as determined by differential scanning calorimetry. Thermal denaturation of holocytochrome b562 is a highly reversible process, and unexpectedly does not involve dissociation of the heme prosthetic group. Thermal denaturation of the corresponding apoprotein, with the heme group chemically removed, remains a cooperative, reversible process. Apocytochrome b562 is substantially destabilized relative to the holoprotein: the t1/2 is more than ten degrees lower, and enthalpy and heat capacity changes are about one-half of the holoprotein values. However, the energetic parameters of apocytochrome b562 denaturation are within the range of observed values for small proteins.
Robinson
C R
CR
Department of Biochemistry, University of Illinois, Champaign 618001, USA.
Liu
Y
Y
O'Brien
R
R
Sligar
S G
SG
Sturtevant
J M
JM
D001059:Apoproteins / Q000737:chemistry; D002152:Calorimetry, Differential Scanning; D003067:Coenzymes / Q000737:chemistry; D003573:Cytochrome b Group / Q000737:chemistry*; D004926:Escherichia coli / Q000737:chemistry*; D029968:Escherichia coli Proteins; D008958:Models, Molecular; D011489:Protein Denaturation; D017510:Protein Folding; D013696:Temperature; D013816:Thermodynamics
D001059:Apoproteins; D003067:Coenzymes; D003573:Cytochrome b Group; D029968:Escherichia coli Proteins; C017850:cytochrome b562, E coli