[Conformational states of the water-soluble fragment of cytochrome b5. I. pH-induced denaturation].
Cytochrome b5 is a membrane protein that comprises two fragments: one is water-soluble and heme-containing, and the other is hydrophobic and membrane-embedded. The function of electron transfer is performed by the former whose crystal structure is known; however, its conformational states when in the membrane field and interacting with other proteins are still to be studied. Previously, we proposed water-alcohol mixtures for modeling the effect of membrane surface on proteins, and used this approach to study the conformational behavior of positively charged cytochrome c as well as relatively neutral retinol-binding protein also functioning in the field of negatively charged membrane. The current study describes the conformational behavior of the negatively charged water-soluble fragment of cytochrome b5 as dependent on pH. Decreasing pH was shown to transform the fragment state from native to intermediate, similar to the molten globule reported earlier for other proteins in aqueous solutions: at pH 3.0, the fragment preserved a pronounced secondary structure and compactness but lost its rigid tertiary structure. A possible role of this intermediate state in cytochrome b5 functioning is discussed.
Basova
L V
LV
Institute of Protein Research, Russian Academy of Sciences, Pushchino, Moscow Region, 142290 Russia.
Il'ina
N B
NB
Vasilenko
K S
KS
Tiktopulo
E I
EI
Bychkova
V E
VE
D002152:Calorimetry, Differential Scanning; D002942:Circular Dichroism; D015786:Cytochromes b5 / Q000737:chemistry* / Q000378:metabolism; D019791:Guanidine / Q000737:chemistry; D006418:Heme / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D010446:Peptide Fragments / Q000737:chemistry; D011487:Protein Conformation; D011489:Protein Denaturation; D012995:Solubility; D013050:Spectrometry, Fluorescence; D014364:Tryptophan / Q000737:chemistry; D014867:Water
D010446:Peptide Fragments; D014867:Water; D006418:Heme; D014364:Tryptophan; D015786:Cytochromes b5; D019791:Guanidine