Selective Recognition of Phosphatidylinositol Phosphate Receptors by C-Terminal Tail of Mitotic Kinesin-like Protein 2 (MKlp2)

Single-particle adsorption of ultra-small gold nanoparticles at the biomembrane phase boundary

Nanomaterials are revolutionizing biomedical research by enabling the development of novel therapies, with applications ranging from drug delivery and diagnostics to the modulation of specific biological processes. Current research focuses on tasks such as enhancing cellular uptake of materials while preserving their functionality. However, the mechanisms governing interactions between nanomaterials and biological systems-particularly cellular membranes-remain challenging to elucidate due to the complex, dynamic nature of the lipid bilayer environment. This complexity arises from factors such as coexisting lipid domains (conserved regions of lipids) or lipid rafts, as well as cellular behaviors that induce state changes. The heterogeneous membrane landscape may offer unique adsorption properties and other functional effects, making it crucial to understand these interactions for greater biological control in nanotherapeutics. In this work, we systematically expose a phase-separated phospholipid-supported lipid bilayer (SLB)-specifically, a fluid-gel DOPC:DPPC bilayer-to low concentrations of citrate-capped 5 nm gold nanoparticles (AuNPs) to observe the adsorption process of individual AuNPs at the molecular scale. Using atomic force microscopy (AFM), we experimentally detect the adsorption of some AuNPs at the phase boundary. Complementary molecular dynamics (MD) simulations further elucidate the mechanism of single AuNP adsorption at lipid phase boundaries. Our findings indicate that the AuNP preferentially incorporates into the fluid-phase DOPC lipids while maintaining partial association with the gel-phase DPPC lipids due to diffusion effects. During adsorption, the AuNP disrupts lipid organization by increasing lateral lipid mixing across the phase boundary. This disruption to lipid molecular ordering is further evident upon AuNP incorporation into the bilayer. The ability to modulate the spatial organization and structure of lipid molecules has significant implications for therapeutics that leverage lipid diffusion pathways for alternative drug delivery mechanisms or to induce specific lipid behaviors.

Molecular and cellular level characterization of cytoskeletal mechanics using a quartz crystal microbalance

A quartz crystal microbalance (QCM) is an instrument that has the ability to measure nanogram-level changes in mass on a quartz sensor and is traditionally used to probe surface interactions and assembly kinetics of synthetic systems. The addition of dissipation monitoring (QCM-D) facilitates the study of viscoelastic systems, such as those relevant to molecular and cellular mechanics. Due to real-time recording of frequency and dissipation changes and single protein-level precision, the QCM-D is effective in interrogating the viscoelastic properties of cell surfaces and in vitro cellular components. However, few studies focus on the application of this instrument to cytoskeletal systems, whose dynamic parts create interesting emergent mechanics as ensembles that drive essential tasks, such as division and motility. Here, we review the ability of the QCM-D to characterize key kinetic and mechanical features of the cytoskeleton through in vitro reconstitution and cellular assays and outline how QCM-D studies can yield insightful mechanical data alone and in tandem with other biophysical characterization techniques.

Behavior of Citrate-Capped Ultrasmall Gold Nanoparticles on a Supported Lipid Bilayer Interface at Atomic Resolution

Nanomaterials have the potential to transform biological and biomedical research, with applications ranging from drug delivery and diagnostics to targeted interference of specific biological processes. Most existing research is aimed at developing nanomaterials for specific tasks such as enhanced biocellular internalization. However, fundamental aspects of the interactions between nanomaterials and biological systems, in particular, membranes, remain poorly understood. In this study, we provide detailed insights into the molecular mechanisms governing the interaction and evolution of one of the most common synthetic nanomaterials in contact with model phospholipid membranes. Using a combination of atomic force microscopy (AFM) and molecular dynamics (MD) simulations, we elucidate the precise mechanisms by which citrate-capped 5 nm gold nanoparticles (AuNPs) interact with supported lipid bilayers (SLBs) of pure fluid (DOPC) and pure gel-phase (DPPC) phospholipids. On fluid-phase DOPC membranes, the AuNPs adsorb and are progressively internalized as the citrate capping of the NPs is displaced by the surrounding lipids. AuNPs also interact with gel-phase DPPC membranes where they partially embed into the outer leaflet, locally disturbing the lipid organization. In both systems, the AuNPs cause holistic perturbations throughout the bilayers. AFM shows that the lateral diffusion of the particles is several orders of magnitude smaller than that of the lipid molecules, which creates some temporary scarring of the membrane surface. Our results reveal how functionalized AuNPs interact with differing biological membranes with mechanisms that could also have implications for cooperative membrane effects with other molecules.