Biology subjects

Walrant, A.

Publications and source records attributed to Walrant, A..

4 recordsLinked to original sources

bioRxiv2025

Membrane partition and structural reorganization induced by anti-psychotics with distinct clinical profiles

Antipsychotics (APs) are used in the treatment of severe mental disorders. Their mechanism of action involves interaction with multiple brain targets, notably the dopamine D2 receptors (D2R), where they compete with dopamine. Due to their lipophilic nature, APs also partition and accumulate in lipid membranes, particularly around the D2R and in synaptic vesicles. When intercalated into brain membranes, APs slowly accumulate and act as a reservoir, allowing their rapid release on demand to modulate neurotransmitter signaling. They also modify the physicochemical and mechanical properties of the lipid bilayer. These modifications can subsequently affect the conformational changes of embedded membrane proteins like the D2R. The present study investigated two major APs with different pharmacological and clinical profiles: chlorpromazine, which exerts its clinical activity mainly through a strong antagonistic action at the D2R, and clozapine, the weakest D2R antagonist of all APs. Surprisingly, although D2R antagonism is usually associated with AP potency, clozapine has repeatedly demonstrated clinical superior efficacy to all APs and is therefore recommended for treatment-resistant schizophrenia. The current work aims to extend the classical AP receptor mediated paradigmatic mode of action to their potential and unique membrane remodeling properties by thoroughly comparing their partitioning and impact on the physicochemical properties of the lipid membrane. Lipid model membranes mimicking synaptic vesicles have been investigated using a combination of several biophysical methods. The study aims to determine how the partitioning of the two APs modifies membrane order, phase transition, thickness, elasticity, phase separation, membrane integrity and charge. Differences have been demonstrated between these two compounds, which may further differ both over time as they accumulate as well as depending on their pre- or post-synaptic location.

biophysics↗

bioRxiv2021

A cationic motif in Engrailed-2 homeoprotein controls its internalization via selective cell-surface glycosaminoglycans interactions

Engrailed-2 (En2) is a transcription factor that possesses as most homeoproteins the unique and intriguing property to transfer from cell to cell through unconventional pathways. The internalization mechanism of this cationic protein is far from being fully understood and is proposed to require an initial interaction with cell-surface glycosaminoglycans (GAGs). To decipher the role of GAGs in the recognition of En2 at the cell surface, we have quantified the internalization of the homeodomain region in cell lines that differ in their content in cell-surface GAGs. The binding specificity to GAGs and the influence of this interaction on the structure and dynamics of En2 was also investigated at the amino acid level. Our results show that a high-affinity GAG-binding hexadecapeptide (RKPKKKNPNKEDKRPR) located upstream of the homeodomain controls internalization efficiency of En2 through selective interactions with highly-sulfated GAGs of heparan sulfate type. Our data underline the functional importance of the intrinsically disordered basic region that precedes the prominent internalization domain in En2, and demonstrate the critical role of GAGs as an entry gate for En2, finely tuning its capacity to internalize into cells.

biochemistry↗

bioRxiv2019

Ionpair-π interactions favor cell penetration of arginine/tryptophan-rich cell-penetrating peptides

Cell-penetrating peptides (CPPs) internalization can occur both by endocytosis and direct translocation through the cell membrane. These different entry routes suggest that molecular partners at the plasma membrane, phospholipids or glycosaminoglycans (GAGs), bind CPPs with different affinity or selectivity. The analysis of sequence-dependent interactions of CPPs with lipids and GAGs should lead to a better understanding of the molecular mechanisms underlying their internalization. CPPs are short sequences generally containing a high number of basic arginines and lysines and sometimes aromatic residues, in particular tryptophans. Tryptophans are crucial residues in membrane-active peptides, because they are important for membrane interaction. Membrane-active peptides often present facial amphiphilicity, which also promote the interaction with lipid bilayers. To study the role of Trp and facial amphiphilicity in cell interaction and penetration of CPPs, a nonapeptide series containing only Arg, Trp or D-Trp residues at different positions was designed. Our quantitative study indicates that to maintain/increase the uptake efficiency, Arg can be advantageously replaced by Trp in the nonapeptides. The presence of Trp in oligoarginines increases the uptake in cells expressing GAGs at their surface, when it only compensates for the loss of Arg and maintains similar peptide uptake in GAG-deficient cells. In addition, we show that facial amphiphilicity is not required for efficient uptake of these nonapeptides. Thermodynamic analyses point towards a key role of Trp that highly contributes to the binding enthalpy of complexes formation. Density functional theory (DFT) analysis highlights that salt bridge-{pi} interactions play a crucial role for the GAG-dependent entry mechanisms.

biochemistry↗

bioRxiv2019

Constrained actin dynamics emerges from variable compositions of actin regulatory protein complexes

Assemblies of actin and its regulators underlie the dynamic morphology of all eukaryotic cells. To begin to understand how diverse regulatory proteins work together to generate actin-rich structures we tracked the assembly of actin regulators and their relative proportions in a cell-free system that generates filopodia-like structures (FLS). We found that heterogeneous mixtures of regulators could give rise to morphologically similar structures and that the FLS actin bundles exhibited simple dynamic behaviour of growth and shrinkage. To explain these observations, we combined experiment with theory, and found that stochastic fluctuations between redundant actin regulatory subcomplexes can account for the actin dynamics. Comparing the localizations of a variety of endogenous actin regulators in Drosophila embryos and distributions of filopodia lengths yielded similar conclusions of heterogenous actin regulatory complexes and filopodia lengths governed by a stochastic growth process. Our results explain how weakly-associating assemblies of regulatory proteins can produce robust functional outcomes.

cell biology↗