Cooperative Unfolding of Compact Conformations of the Intrinsically Disordered Protein Osteopontin

Abstract

Intrinsically disordered proteins (IDPs) constitute a class of biologically active proteins that lack defined tertiary and often secondary structure. The IDP Osteopontin (OPN), a cytokine involved in metastasis of several types of cancer, is shown to simultaneously sample extended, random coil-like conformations and stable, cooperatively folded conformations. By a combination of two magnetic resonance methods, electron paramagnetic resonance and nuclear magnetic resonance spectroscopy, we demonstrate that the OPN ensemble exhibits not only characteristics of an extended and flexible polypeptide, as expected for an IDP, but also simultaneously those of globular proteins, in particular sigmoidal structural denaturation profiles. Both types of states, extended and cooperatively folded, are populated simultaneously by OPN in its apo state. The heterogeneity of the structural properties of IDPs is thus shown to even involve cooperative folding and unfolding events.

Compensatory Adaptations of Structural Dynamics in an Intrinsically Disordered Protein Complex

“…While detailed characterization and analysis of the DEER time traces of the OPN apo state have already been reported, [11] here the DEER data were recorded in the absence and the presence of heparin. All DEER data are shown in the Supporting Information.…”

“…[11] D eff denotes the total signal decay at the experimental DEER evolution time (see the Supporting Information) and is an approximate measure of the average interspin distance for broad P(R) distributions. [11] For increasing interspin mean distance R between two labeling sites D eff typically decreases.…”

Protein Folding, Misfolding, Aggregation And Amyloid Formation: Mechanisms of Aβ Oligomer Mediated Toxicities

“…Such partially unfolded/misfolded intermediates are populated under denaturing conditions. Contrary to this belief, recent studies have shown that denaturation of IDP Osteopontin (OPN), lead to formation of extended, random coil-like conformation and stable, cooperatively many folded conformation [14] . Further, these IDPs are associated with human diseases, including cancer, cardiovascular disease, amyloidoses, neurodegenerative diseases, and diabetes.…”

Dynamic footprint of sequestration in the molecular fluctuations of osteopontin

“…Some IDPs gain structure upon binding and undergo a disorder-to-order transition [32][33][34], while other observations support the existence of 'fuzzy complexes' where such transitions do not occur [35]. The latter was the case for a fuzzy complex with an OPN fragment, where an increase in disorder was observed when bound to heparin [36]. OPN has been called a molecule for all seasons [37].…”

“…Fisher et al [10] determined, using 1-D 1 H NMR and transverse relaxation times, that the solution structure of native OPN was consistent with that of an IDP. Kurzbach [36] combined electron paramagnetic resonance (EPR) and NMR techniques to show that different OPN compact and extended conformations can interconvert through cooperative phase transitions. Yamaguchi et al [43] have shown that recombinant mouse OPN exhibits a transient long-range intramolecular interaction between its N-and Cterminal regions that can shield the central part of the chain from integrin interactions.…”