Effects of environmental factors on MSP21–25 aggregation indicate the roles of hydrophobic and electrostatic interactions in the aggregation process

Abstract

Merozoite surface protein 2 (MSP2), one of the most abundant proteins on the merozoite surface of Plasmodium falciparum, is recognized to be important for the parasite's invasion into the host cell and is thus a promising malaria vaccine candidate. However, mediated mainly by its conserved N-terminal 25 residues (MSP21-25), MSP2 readily forms amyloid fibril-like aggregates under physiological conditions in vitro, which impairs its potential as a vaccine component. In addition, there is evidence that MSP2 exists in aggregated forms on the merozoite surface in vivo. To elucidate the aggregation mechanism of MSP21-25 and thereby understand the behavior of MSP2 in vivo and find ways to avoid the aggregation of relevant vaccine in vitro, we investigated the effects of agitation, pH, salts, 1-anilinonaphthalene-8-sulfonic acid (ANS), trimethylamine N-oxide dihydrate (TMAO), urea, and sub-micellar sodium dodecyl sulfate (SDS) on the aggregation kinetics of MSP21-25 using thioflavin T (ThT) fluorescence. The results showed that MSP21-25 aggregation was accelerated by agitation, while repressed by acidic pHs. The salts promoted the aggregation in an anion nature-dependent pattern. Hydrophobic surface-binding agent ANS and detergent urea repressed MSP21-25 aggregation, in contrast to hydrophobic interaction strengthener TMAO, which enhanced the aggregation. Notably, sub-micellar SDS, contrary to its micellar form, promoted MSP21-25 aggregation significantly. Our data indicated that hydrophobic interactions are the predominant driving force of the nucleation of MSP21-25 aggregation, while the elongation is controlled mainly by electrostatic interactions. A kinetic model of MSP21-25 aggregation and its implication were also discussed.

Identification of fibrillogenic regions in human triosephosphate isomerase

“…Higher concentrations of urea did not increase β -aggregation ( Fig. S2 ), as expected, since urea can solvate the main-chain and compete for hydrogen bonds during β -aggregation ( Cai et al, 2014 ; Hamada & Dobson, 2002 ; Zhang et al, 2014 ). In addition to ThT fluorescence, HsTPI urea aggregates were analyzed by ATR-FTIR demonstrating formation of new β -structure with a characteristic lower-frequency band position around 1,624 cm −1 indicative of cross- β formation ( Moran & Zanni, 2014 ; Zandomeneghi et al, 2004 ).…”

Peer Review #1 of "Identification of fibrillogenic regions in human triosephosphate isomerase (v0.1)"

“…On the other hand, the slightly destabilization of HsTPI structure with 3.2 M urea (Mainfroid et al, 1996a) showed an increase in β-aggregation according to ThT fluorescence intensities ( Figure 1A) suggesting that native state is protected by a high energy barrier that impedes the exploration of intermediate states susceptible to β-aggregation. Higher concentrations of urea did not increase β-aggregation (Supplemental Figure S2), as expected, since urea can solvate the main-chain and compete for hydrogen bonds during β-aggregation (Cai et al, 2014;Hamada & Dobson, 2002;Zhang et al, 2014). In addition to ThT fluorescence, HsTPI urea aggregates were analyzed by ATR-FTIR demonstrating formation of new β-structure with a characteristic lowerfrequency band position around 1624 cm -1 indicative of cross-β formation (Moran & Zanni, 2014;Zandomeneghi et al, 2004).…”