Effect of Self-Association on the Structural Organization of Partially Folded Proteins: Inactivated Actin

Abstract

The propensity to associate or aggregate is one of the characteristic properties of many nonnative proteins. The aggregation of proteins is responsible for a number of human diseases and is a significant problem in biotechnology. Despite this, little is currently known about the effect of self-association on the structural properties and conformational stability of partially folded protein molecules. G-actin is shown to form equilibrium unfolding intermediate in the vicinity of 1.5 M guanidinium chloride (GdmCl). Refolding from the GdmCl unfolded state is terminated at the stage of formation of the same intermediate state. An analogous form, known as inactivated actin, can be obtained by heat treatment, or at moderate urea concentration, or by the release of Ca(2+). In all cases actin forms specific associates comprising partially folded protein molecules. The structural properties and conformational stability of inactivated actin were studied over a wide range of protein concentrations, and it was established that the process of self-association is rather specific. We have also shown that inactivated actin, being denatured, is characterized by a relatively rigid microenvironment of aromatic residues and exhibits a considerable limitation in the internal mobility of tryptophans. This means that specific self-association can play an important structure-forming role for the partially folded protein molecules.

Metal-triggered Structural Transformations, Aggregation, and Fibrillation of Human α-Synuclein

“…Aggregation or self-association is a characteristic property of partially folded (denatured) proteins (68 -72). It has been shown that in some cases the self-association induces additional structure and stability in the partially folded intermediates (73)(74)(75). Table I shows the far-UV CD parameters of ␣-synuclein determined at different protein concentrations and indicates that the spectrum is not affected by an ϳ170-fold increase in protein concentration, consistent with the lack of self-association up to at least 600 M. Fig.…”

Dissecting the Alternatively Folded State of the Antibody Fab Fragment

“…The structures adopted by antibodies at low pH are set apart from those of many other proteins [35][36][37] in that they are remarkably stable against unfolding and that they are oligomeric. In the original experiments performed with a complete IgG antibody, 13 it was not clear whether all domains of the antibody contribute to this structural state.…”

Development of free-energy-based models for chaperonin containing TCP-1 mediated folding of actin

“…The intermediate I 3 is formed when actin is unfolded in the presence of EDTA or as a result of heat denaturation, moderate denaturant concentration, by dialysis from high concentration of denaturant and spontaneously during storage . At moderate to high protein concentrations, irreversible aggregation of this species occurs (Bertazzon et al 1990;Kuznetsova et al 1999). The I 1 $ATP $$% !$$ I 2 C ATP equilibrium is rapidly established relative to the other steps (Kinosian et al 1993), and based on this assumption our stopped-flow fluorescence study has verified the reaction scheme and calculated the kinetic parameters (Altschuler et al 2005).…”