PHYSICAL-CHEMICAL PROPERTIES OF ACTIN IN DIFFERENT STRUCTURAL STATES. NEW IDEAS ABOUT
ITS FOLDING-UNFOLDING PATHWAYS
O. I. Povarova, I. M. Kuznetsova, K. K. Turoverov
Institute of Cytology, RAS, St. Petersburg, Russia;
e-mail: kkt@mail.cytspb.rssi.ru
Results of actin folding-unfolding pathways examination and characterization of intermediate and misfolded states
are summarized. Properties of microenvironments and peculiarities of location of tryptophan residues in protein are analysed in
detail. This allowed to conclude that the main contribution to the bulk fluorescence of native protein is made by internal
tryptophan residues Trp 340 and Trp 356, localized in hydrophobic regions, while tryptophan residues Trp 79 and Trp 86 are
quenched. It has been shown that inactivated actin, previously regarded as an intermediate state between native and completely
unfolded state of protein is in reality a misfolded aggregated state. The properties of actin in this state were characterized in
detail. In particular, it is shown that inactivated actin is a monodisperse associate consisting of 15 monomer unit. Two earlier
unknown intermediate states, which precede completely unfolding of protein macromolecule and formation of inactivated actin, were
visualized. A new scheme of folding-unfolding processes was proposed. It is shown that the reason of anomalous effects, which are
recorded for actin in solutions with small concentrations of GdnHCl, is a specific interaction of actin with a denaturant.
Key words: actin, protein, folding, intermediate states, kinetics of denaturation, intrinsic fluorescence of
proteins, inactivated actin
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