Enthalpically driven peptide stabilization by protective osmolytes

Politi, Regina; Harries, Daniel

doi:10.1039/c0cc01763a

Cited by 107 publications

(163 citation statements)

References 25 publications

(18 reference statements)

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“…The second difficulty is that observed effects of osmolytes and crowders on protein binding and folding often have significant enthalpic contributions (23,(37)(38)(39). Excluded volume effects are entropic, whether treated by the mean-field AO, scaled particle, or HS mixture models.…”

Section: Discussionmentioning

confidence: 99%

Analysis of the size dependence of macromolecular crowding shows that smaller is better

Sharp

2015

Proc. Natl. Acad. Sci. U.S.A.

139

129

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The aqueous milieu inside cells contains as much as 30-40% dissolved protein and RNA by volume. This large concentration of macromolecules is expected to cause significant deviations from solution ideality. In vivo biochemical reaction rates and equilibria might differ significantly from those measured in the majority of in vitro experiments that are performed at much lower macromolecule concentrations. Consequently crowding, a nonspecific phenomenon believed to arise from the large excluded volume of these macromolecules, has been studied extensively by experimental and theoretical methods. However, the relevant theory has not been applied consistently. When the steric effects of macromolecular crowders and small molecules like water and ions are treated on an equal footing, the effect of the macromolecules is opposite to that commonly believed. Large molecules are less effective at crowding than water and ions. There is also a surprisingly weak dependence on crowder size. Molecules of medium size, ∼5 Å radius, have the same effect as much larger macromolecules like proteins and RNA. These results require a reassessment of observed high-concentration effects and of strategies to mimic in vivo conditions with in vitro experiments. T he milieu inside cells contains a large amount of solutes that include small ions, metabolites, and macromolecules. Typical protein/RNA concentrations range from 300 mg/mL to 400 mg/mL or about 30-40% by weight. These are 10-fold or more higher than the macromolecular concentrations usually encountered in in vitro measurements and could lead to significant nonideality in solution behavior. The possibility that in vivo biochemical reaction rates and equilibria might be quite different from measured values due to this nonideality has stimulated considerable research. Macromolecular crowding in particular has stimulated a large number of studies, which have been extensively reviewed (1-5). Crowding has been variously described as physical occupation of volume by the macromolecules, which is then unavailable to other molecules, as an excluded volume effect, as a nonspecific effect due to steric repulsion, and as eliminating positions at which the protein can be placed (2, 5, 6). The other contribution to nonideality is from interactions between various solution components, either attractive or repulsive-repulsive interactions distinct from the van der Waals core repulsion or steric factor underlying crowding. We know very little about the contribution of intersolute interactions to nonideality in vivo. Crowding has been more extensively studied because the steric or excluded volume of a macromolecule is a welldefined property, it is always present, and its qualitative effect on biochemical reactions seems obvious (2). However, as I demonstrate in this paper, the effect of crowding macromolecules on a biochemical reaction is not obvious, the relevant theory has not been consistently applied, and indeed the effect is opposite to that commonly believed.Analyses of the effect of crowding mac...

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Section: Discussionmentioning

confidence: 99%

Analysis of the size dependence of macromolecular crowding shows that smaller is better

Sharp

2015

Proc. Natl. Acad. Sci. U.S.A.

139

129

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“…Using a β-hairpin peptide as a test molecule, the Harries group (Politi and Harries 2010;Sukenik et al 2012) observed stabilizing effects for small polyol osmolytes and the synthetic polymers, polyethylene glycol and dextran. The enthalpic components differed for the two classes of cosolute.…”

Section: Enthalpy and Entropymentioning

confidence: 99%

Soft interactions and crowding

2013

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The intracellular milieu is complex, heterogeneous and crowded-an environment vastly different from dilute solutions in which most biophysical studies are performed. The crowded cytoplasm excludes about a third of the volume available to macromolecules in dilute solution. This excluded volume is the sum of two parts: steric repulsions and chemical interactions, also called soft interactions. Until recently, most efforts to understand crowding have focused on steric repulsions. Here, we summarize the results and conclusions from recent studies on macromolecular crowding, emphasizing the contribution of soft interactions to the equilibrium thermodynamics of protein stability. Despite their non-specific and weak nature, the large number of soft interactions present under many crowded conditions can sometimes overcome the stabilizing steric, excluded volume effect.

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“…This effect is achieved because of the preferential exclusion of osmolytes from the protein interface that stabilizes protein states with smaller accessible surface area. 11,[13][14][15][16][17][18][19] Taken together, this wide range of cellular cosolutes presents a highly elaborate environment for the processes that lead to amyloid formation.…”

Section: Different Cosolutes Distinctively Affect Aggregation Kineticsmentioning

confidence: 99%

“…14,20,28 The cosolutes included polyols and PEGs of different molecular weights. The aggregation process was followed using several experimental techniques, including circular dichroism, electron microscopy and ThT fluorescence.…”

Section: Different Cosolutes Distinctively Affect Aggregation Kineticsmentioning

confidence: 99%

Insights into the disparate action of osmolytes and macromolecular crowders on amyloid formation

Sukenik

Harries

2012

Prion

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It is widely recognized that amyloid formation sensitively responds to conditions set by myriad cellular solutes. These cosolutes include two important classes: macromolecular crowders and compatible osmolytes. We have recently found that addition of macromolecular PEG only slightly affects fibril formation of a model peptide in vitro. Polyol osmolytes, in contrast, lengthen the lag time for aggregation, and lead to larger fibril mass at equilibrium. To further hypothesize on the molecular underpinnings of the disparate effect of the two cosolute classes, we have further analyzed the experiments using an available kinetic mechanism describing fibril aggregation. Model calculations suggest that all cosolutes similarly lengthen the time required for nucleation, possibly due to their excluded volume effect. However, PEGs may in addition promote fibril fragmentation, leading to lag times that are overall almost unvaried. Moreover, polyols effectively slow the monomer-fibril detachment rates, thereby favoring additional fibril formation. Our analysis provides first hints that cosolutes act not only by changing association or dissociation rates, but potentially also by directing the formation of fibrils of varied morphologies with different mechanical properties. Although additional experiments are needed to unambiguously resolve the action of excluded cosolutes on amyloid formation, it is becoming clear that these compounds are important to consider in the search for ways to modulate fibril formation.

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Enthalpically driven peptide stabilization by protective osmolytes

Cited by 107 publications

References 25 publications

Analysis of the size dependence of macromolecular crowding shows that smaller is better

Analysis of the size dependence of macromolecular crowding shows that smaller is better

Soft interactions and crowding

Insights into the disparate action of osmolytes and macromolecular crowders on amyloid formation

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