Probing the Influence of Citrate-Capped Gold Nanoparticles on an Amyloidogenic Protein

Abstract

Nanoparticles (NPs) are known to exhibit distinct physical and chemical properties compared with the same materials in bulk form. NPs have been repeatedly reported to interact with proteins, and this interaction can be exploited to affect processes undergone by proteins, such as fibrillogenesis. Fibrillation is common to many proteins, and in living organisms, it causes tissue-specific or systemic amyloid diseases. The nature of NPs and their surface chemistry is crucial in assessing their affinity for proteins and their effects on them. Here we present the first detailed structural characterization and molecular mechanics model of the interaction between a fibrillogenic protein, β2-microglobulin, and a NP, 5 nm hydrophilic citrate-capped gold nanoparticles. NMR measurements and simulations at multiple levels (enhanced sampling molecular dynamics, Brownian dynamics, and Poisson-Boltzmann electrostatics) explain the origin of the observed protein perturbations mostly localized at the amino-terminal region. Experiments show that the protein-NP interaction is weak in the physiological-like, conditions and do not induce protein fibrillation. Simulations reproduce these findings and reveal instead the role of the citrate in destabilizing the lower pH protonated form of β2-microglobulin. The results offer possible strategies for controlling the desired effect of NPs on the conformational changes of the proteins, which have significant roles in the fibrillation process.

Short-Chain Alkanethiol Coating for Small-Size Gold Nanoparticles Supporting Protein Stability

“…The fluorescence of W60G variant is, indeed, approximately 20% lower than the value of wild-type protein. This result is consistent with a strong localization of the electrostatic interaction, probably being due to the compactness of the NP electron plasma [14,15]. The character of the interaction surface, as described in Figure 6, can be appreciated when compared to the β2m regions that are involved in the contacts with the heavy chain of type I major histocompatibility complex (MHC-I) [19].…”

“…In patients that are affected by chronic renal failure, it accumulates in the blood and precipitates into amyloid deposits in correspondence of the joints. In literature, the interaction between β2m and citrate-stabilized AuNPs (Cit-AuNPs) was reported for both the wild-type and D76N variants [14,15]. In both of the cases, a labile interaction was observed that does not affect the overall folding and is mainly located at the N-terminal apical part of the protein structure.…”

“…This adjustment leads to 9-12 tetramers per NP that means 36-48 monomers. If the ratio between the NP surface area and the cylindroid base is considered, then the number of protein monomers per NP is reduced to [14][15][16][17][18][19][20][21][22]. From all of these considerations, beyond any critical evaluation, the number of β2m molecules that can be adsorbed on a MPA-AuNP goes from 14 to 50, approximately.…”

Modeling and simulation of protein–surface interactions: achievements and challenges

“…Examples include simulations for structural refinement of docked complexes (Aliaga et al 2011;Alvarez-Paggi et al 2013;Brancolini et al 2012Brancolini et al , 2015Imamura et al 2007), and for the investigation of the binding orientations of proteins on surfaces (Alvarez-Paggi et al 2010;Boughton et al 2010;Coppage et al 2013); the kinetic mechanisms of adsorption (Raffaini & Ganazzoli, 2010); the ET pathways and properties of adsorbed proteins (Bizzarri, 2006;Siwko & Corni, 2013;Utesch et al 2012;Zanetti-Polzi et al 2014;Zhou et al 2004); the effects of pH (Emami et al 2014b;Imamura et al 2003;Tosaka et al 2010;Utesch et al 2013) and ionic strength (Bizzarri, 2006) on adsorption; the role of ions in mediating adsorption ; and structural and energetic aspects of adsorption of proteins on surfaces (Apicella et al 2013;Jose & Sengupta, 2013;Hoefling et al 2011;Hung et al 2011;Kubiak-Ossowska & Mulheran, 2010a, b;O'Mahony et al 2013;Vila Verde et al 2009Wang et al 2010a, b;Yu et al 2012a;Steckbeck et al 2014;Sun et al 2014a;Sun et al 2014b). Further, conventional MD can be used to simulate physical perturbations, such as mechanical or electrical forces exerted on molecules in experiments.…”

“…Brancolini and coworkers employed BD simulations for docking of ubiquitin ) and of human β2-microglobulin (Brancolini et al , 2015Brancolini et al 2015) on bare, citrate covered and thiol-protected gold nanoparticles using the ProMetCS model (Kokh et al 2010). The most abundant orientations of ubiquitin on the gold obtained from BD simulations were used as starting orientations for fully flexible MD simulations.…”