Changes of structure and intramolecular mobility in the course of actin denaturation.
Rabbit skeletal muscle G-actin on heating is transformed into the G1-state in which the intrinsic fluorescence spectrum is shifted to a longer wavelength compared with that of native actin, but of much shorter wavelength than that of actin in 8 M urea. A structure with fluorescence characteristics identical to those of the G1-form appears upon the removal of Ca2+, upon partial denaturation in 3-5 M urea and renaturation from the completely unfolded form in 8 M urea as well as spontaneously during storage of actin solutions. All this allows us to regard the G1-form of the actin macromolecule as an "intermediate" state. However, in contrast to other proteins in the intermediate state, a band of the CD spectrum has been observed for G1-actin, with an amplitude comparable to that of native proteins in the region where aromatic groups absorb. This points to a relatively low level of intramolecular mobility of the side chains in this structural state of actin. Moreover, according to polarized fluorescence measurements, the G-G1 transition is accompanied not by an increase - as would have been expected, but by a decrease in mobility of the tryptophan residues. The data obtained confirm the previously observed regularity of the intramolecular mobility of tryptophan residues in a hydrophobic environment being often greater than that of tryptophan residues whose microenvironment is formed by polar protein groups.
Kuznetsova
I M
IM
Institute of Cytology, Academy of Sciences of the U.S.S.R., Leningrad.
Khaitlina SYu
Konditerov
S N
SN
Surin
A M
AM
Turoverov
K K
KK
D000199:Actins / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002942:Circular Dichroism; D009132:Muscles / Q000378:metabolism; D011487:Protein Conformation; D011489:Protein Denaturation; D011817:Rabbits; D013050:Spectrometry, Fluorescence; D014364:Tryptophan
D000199:Actins; D014364:Tryptophan; D002118:Calcium