Interaction of toxic and non-toxic HypF-N oligomers with lipid bilayers investigated at high resolution with atomic force microscopy

Abstract

Protein misfolded oligomers are considered the most toxic species amongst those formed in the process of amyloid formation and the molecular basis of their toxicity, although not completely understood, is thought to originate from the interaction with the cellular membrane. Here, we sought to highlight the molecular determinants of oligomer-membrane interaction by atomic force microscopy. We monitored the interaction between multiphase supported lipid bilayers and two types of HypF-N oligomers displaying different structural features and cytotoxicities. By our approach we imaged with unprecedented resolution the ordered and disordered lipid phases of the bilayer and different oligomer structures interacting with either phase. We identified the oligomers and lipids responsible for toxicity and, more generally, we established the importance of the membrane lipid component in mediating oligomer toxicity. Our findings support the importance of GM1 ganglioside in mediating the oligomer-bilayer interaction and support a mechanism of oligomer cytotoxicity involving bilayer destabilization by globular oligomers within GM1-rich ordered raft regions rather than by annular oligomers in the surrounding disordered membrane domains.

Soluble Oligomers Require a Ganglioside to Trigger Neuronal Calcium Overload

“…Our results agree with these considerations; in fact, we showed that A␤ 42 oligomers display an increased tendency to interact with SUVs as far as GM1 abundance is raised, supporting the idea that aggregate binding is not only driven by the presence of membrane protein targets [64]. The increase in GM1 content appears to affect clustering and enlargement of existing raft platforms, or to induce the formation of new ones [2].…”

“…The affinity of protein aggregates for membrane GM1 was suggested to involve the negative charge of the sialic acid [63,64]. Our results agree with these considerations; in fact, we showed that A␤ 42 oligomers display an increased tendency to interact with SUVs as far as GM1 abundance is raised, supporting the idea that aggregate binding is not only driven by the presence of membrane protein targets [64].…”

Oleuropein aglycone: A polyphenol with different targets against amyloid toxicity

“…The calculated difference in thickness between L β and L α domains (∆Z) was 2.2±0.2 nm; this value, very reproducible for both untreated SLBs and OleA-treated SLBs (Fig. 4E,G), agrees with previous data [37] and was monitored to evaluate structural perturbations induced by the interaction of D76N b2m with the bilayer. We found that 144 h-aged aggregates grown in the absence of OleA were accumulating on the GM1-enriched L β domains (Fig.…”

Toxic HypF-N Oligomers Selectively Bind the Plasma Membrane to Impair Cell Adhesion Capability

“…The two oligomeric forms, named type A oligomer (OA) and type B oligomer (OB) and grown under different solution conditions from the N-terminal domain of the Escherichia coli protein HypF (HypF-N), have provided a remarkable contribution to our understanding of the oligomer structure-cytotoxicity relationship (13)(14)(15)(16)(17)(18)(19)(20). In particular, this system has allowed us to gain significant insight into the structural and biophysical determinants underlying the interaction of protein-misfolded oligomers with the cell membrane, in most cases the earliest event in oligomermediated cytotoxicity (13)(14)(15)(16)(17)(18)(19)(20). Both OAs and OBs bind weakly, but significantly, to thioflavin T and display a roughly spherical shape with a height of 2-6 nm as determined by atomic force microscopy (AFM) (13).…”