Abstract
Interrupted Hydrogen/Deuterium Exchange Reveals the Stable Core of the Remarkably Helical Molten Globule of α-β Parallel Protein Flavodoxin
Highlights
Upon descending the folding funnel, proteins encounter folding energy landscapes that are rough [20, 21]
The proteins consist of a single structural domain and adopt the flavodoxin-like or ␣- parallel topology (Fig. 1), which is characterized by a parallel -sheet that is surrounded by ␣-helices and is widely prevalent in nature
Spectroscopic data show that the off-pathway folding species of flavodoxin is molten globule-like; its hydrodynamic radius is closer to the native state than to the unfolded state, its three tryptophans are solvent-exposed, and it has severely broadened NMR resonances due to exchange between different conformers on the micro- to millisecond time scale [18, 29, 30]
Summary
H/D exchange, hydrogen/deuterium exchange; GdnHCl, guanidine HCl; HSQC, heteronuclear single quantum coherence; PUF, partially unfolded form. Spectroscopic data show that the off-pathway folding species of flavodoxin is molten globule-like; its hydrodynamic radius is closer to the native state than to the unfolded state, its three tryptophans are solvent-exposed, and it has severely broadened NMR resonances due to exchange between different conformers on the micro- to millisecond time scale [18, 29, 30]. Use is made of Tyr44flavodoxin, in which Phe is substituted for Tyr44 This substitution leads to severe destabilization of native apoflavodoxin against unfolding and only marginally affects the stability of the molten globule [34]. We use the interrupted H/D exchange methodology [13, 35, 36] to reveal the stable core of the molten globule of Tyr44-flavodoxin and discuss why this species needs to unfold to produce native flavodoxin
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