Refolding of beta-lactoglobulin studied by stopped-flow circular dichroism at subzero temperatures.
Refolding of bovine beta-lactoglobulin was studied by stopped-flow circular dichroism at subzero temperatures. In ethylene glycol 45%-buffer 55% at -15 degrees C, the isomerization rate from the kinetic intermediate rich in alpha-helix to the native state is approximately 300-fold slower than that at 4 degrees C in the absence of ethylene glycol, whereas the initial folding is completed within the dead time of the stopped-flow apparatus (10 ms). At -28 degrees C, we observed at least three phases; the fastest process, accompanied by an increase of alpha-helix content, is completed within the dead time of the stopped-flow apparatus (10 ms), the second phase, accompanied by an increase of alpha-helix content with the rate of 2 s(-1), and the third phase, accompanied by a decrease of alpha-helix content. This last phase, corresponding to the isomerization process at -15 degrees C described above, was so slow that we could not monitor any changes within 4 h. Based on the findings above, we propose that rapid alpha-helix formation and their concurrent collapse are common even in proteins rich in beta-structure in their native forms.
Qin
Z
Z
Department of Physics, Kansai Medical University, Hirakata, Japan.
Hu
D
D
Shimada
L
L
Nakagawa
T
T
Arai
M
M
Zhou
J M
JM
Kihara
H
H
D002942:Circular Dichroism; D019855:Ethylene Glycol / Q000737:chemistry; D007782:Lactoglobulins / Q000737:chemistry*; D011487:Protein Conformation; D017510:Protein Folding; D013696:Temperature
D007782:Lactoglobulins; D019855:Ethylene Glycol