Electrostatic Effects in Filamentous Protein Aggregation

Abstract

Electrostatic forces play a key role in mediating interactions between proteins. However, gaining quantitative insights into the complex effects of electrostatics on protein behavior has proved challenging, due to the wide palette of scenarios through which both cations and anions can interact with polypeptide molecules in a specific manner or can result in screening in solution. In this article, we have used a variety of biophysical methods to probe the steady-state kinetics of fibrillar protein self-assembly in a highly quantitative manner to detect how it is modulated by changes in solution ionic strength. Due to the exponential modulation of the reaction rate by electrostatic forces, this reaction represents an exquisitely sensitive probe of these effects in protein-protein interactions. Our approach, which involves a combination of experimental kinetic measurements and theoretical analysis, reveals a hierarchy of electrostatic effects that control protein aggregation. Furthermore, our results provide a highly sensitive method for the estimation of the magnitude of binding of a variety of ions to protein molecules.

Protective hinge in insulin opens to enable its receptor engagement

“…That hinge opening enhances susceptibility to fibrillation is in accordance with the stereospecific effects of L-and D-Ala substitutions at B24: although these diastereomers exhibit similar thermodynamic stabilities, the lag time of the (active) D-Ala B24 analog (with unstructured B20-B30 segment) is threefold shorter than that of the (inactive) LAla B24 analog, whose hinge is partially closed (6). It would be of future interest to dissect which individual kinetic steps in the mechanism of insulin fibrillation (54,55) are influenced by substitutions at position B24 in relation to the dynamics of hinge opening. Such analogs provide a model of segmental disorder, a general feature of mutant proteins associated with diverse diseases of toxic protein misfolding and amyloid deposition (29).…”

Solution conditions define morphological homogeneity of α-synuclein fibrils

“…In general, higher salt concentrations lead to faster self-assembly [45,[51][52][53][54]. This enhanced aggregation rate is attributed to sufficient charge screening at higher salt concentrations thus reducing the repulsive forces among the monomers and facilitating intra and intermolecular interactions governed by hydrophobicity [34,55].…”

Protein charge ladders reveal that the net charge of ALS‐linked superoxide dismutase can be different in sign and magnitude from predicted values

“…2,6 For example, less than 10% of ALS-SOD1 mutations increase formal net negative charge 3,4 and those that do (such as V7E or N139D) also reduce the thermostability of holo-SOD1 and/or apo-SOD1. 8 More general support for the electrostatic repulsion hypothesis can be found throughout protein science, [9][10][11] from the century-old observation that proteins precipitate rapidly at their isoelectric point, 12,13 to the measured rates of amyloid formation among non-isoelectric variants, 11,14 to the engineering of "supercharged" proteins that are impervious to self-assembly. 15 Because intermolecular electrostatic interactions persist through physiological buffer across long distances (the Debye radius, j 21 5 10 Å at e 5 80,…”

“…, it is not immediately clear whether "cryptic" mutations would accelerate selfassembly by minimizing long-range electrostatic repulsions-that depend upon the protein's net charge, as reported for other proteins [9][10][11]16 -or by minimizing specific, shorter-range repulsions that depend upon local patterns of charge (e.g., in-register or out-of-register patterns, per structure of the fibril 17,18 ). Regardless of which (or whether) one scenario predominates, quantifying how ALS mutations affect the electrostatic surface potential of SOD1 in its native state will answer several important questions.…”