Critical Balance of Electrostatic and Hydrophobic Interactions Is Required for β₂-Microglobulin Amyloid Fibril Growth and Stability

Abstract

Investigation of factors that modulate amyloid formation of proteins is important to understand and mitigate amyloid-related diseases. To understand the role of electrostatic interactions and the effect of ionic cosolutes, especially anions, on amyloid formation, we have investigated the effect of salts such as NaCl, NaI, NaClO(4), and Na(2)SO(4) on the amyloid fibril growth of beta(2)-microglobulin, the protein involved in dialysis-related amyloidosis. Under acidic conditions, these salts exhibit characteristic optimal concentrations where the fibril growth is favored. The presence of salts leads to an increase in hydrophobicity of the protein as reported by 8-anilinonaphthalene-1-sulfonic acid, indicating that the anion interaction leads to the necessary electrostatic and hydrophobic balance critical for amyloid formation. However, high concentrations of salts tilt the balance to high hydrophobicity, leading to partitioning of the protein to amorphous aggregates. Such amorphous aggregates are not competent for fibril growth. The order of anions based on the lowest concentration at which fibril formation is favored is SO(4)(2)(-) > ClO(4)(-) > I(-) > Cl(-), consistent with the order of their electroselectivity series, suggesting that preferential anion binding, rather than general ionic strength effect, plays an important role in the amyloid fibril growth. Anion binding is also found to stabilize the amyloid fibrils under acidic condition. Interestingly, sulfate promotes amyloid growth of beta(2)-microglobulin at pH between 5 and 6, closer to its isoelectric point. Considering the earlier studies on the role of glycosaminoglycans and proteoglycans (i.e., sulfated polyanions) on amyloid formation, our study suggests that preferential interaction of sulfate ions with amyloidogenic proteins may have biological significance.

Application and use of differential scanning calorimetry in studies of thermal fluctuation associated with amyloid fibril formation

“…0.5 M NaCl), β 2 -m forms spontaneously WL fibrils without the definite nucleation step characterized by a lag period (Fig. 4a-1) (Hong et al 2002;Raman et al 2005;Gosal et al 2005). The C p,app trace of the WL fibrils shows an endothermic peak at about 85°C, which represents fibril depolymerization (line 4 in Fig.…”

“…Amyloid fibril formation of β 2 -m, which is the light chain of the major histocompatibility complex class I molecules (Bjorkman et al 1987), has been studied extensively because of its clinical importance associated with dialysis-related amyloidosis Radford et al 2005;Stoppini et al 2005;Yamamoto and Gejyo 2005;Eichner and Radford 2011b). It is now known that at pH 2.5, β 2 -m is acidunfolded, and two types of fibrils are formed through a lag phase-and a non-lag phase-dependent kinetics, based on a careful choice of salt concentrations (Hong et al 2002;Gosal et al 2005;Raman et al 2005). The lag phasedependent reaction route produces mature amyloid fibrils with a long (approx.…”

Ion‐specific modulation of protein interactions: Anion‐induced, reversible oligomerization of a fusion protein

“…Ions have been observed to impact protein stability, 3 fibril formation, [4][5][6] reversible self-association, [7][8][9] and even protein solution rheology. 10,11 An ion-specific dependence is often discussed in terms of the Hofmeister effect or the electroselectivity series; [3][4][5][12][13][14] however, the exact nature of ion-protein interactions remains unresolved. The classical view holds that such interactions are mediated indirectly through the alteration of bulk water structure, 15 although there is increasing recognition that ions interact directly with proteins.…”

Salts drive controllable multilayered upright assembly of amyloid-like peptides at mica/water interface

“…Salt ions, with their ubiquitous presence in physiological environments, play a critical role in both assembly dynamics and structure (19)(20)(21)(22)(23)(24). In addition to the nonspecific Debye-Hückel screening, specific ionic interactions (i.e., electroselective series) and indirect/direct effects from water structure (i.e., Hofmeister series) have been explored extensively to interpret salt effects (19-24).…”

“…Salt ions, with their ubiquitous presence in physiological environments, play a critical role in both assembly dynamics and structure (19)(20)(21)(22)(23)(24). In addition to the nonspecific Debye-Hückel screening, specific ionic interactions (i.e., electroselective series) and indirect/direct effects from water structure (i.e., Hofmeister series) have been explored extensively to interpret salt effects (19)(20)(21)(22)(23)(24). For example, the α-syn fibrillization follows the Hofmeister series but not the electroselective series (19), whereas the opposite seems to be true for other proteins, such as glucagon (21), β2-microglobulin (20), and mouse prionic protein (24), indicating the complex nature of the salt effect on molecular assembly.…”