High Aspect Ratio-Nanostructured Surfaces as Biological Metamaterials

Materials patterned with high-aspect-ratio nanostructures have features on similar lengthscales to cellular components. These surfaces are an extreme topography on the cellular level and have become useful tools for perturbing and sensing the cellular environment. Motivation comes from the ability of high-aspect-ratio nanostructures to deliver cargoes into cells and tissues, access the intracellular environment, and control cell behavior. These structures directly perturb cells’ ability to sense and respond to external forces, influencing cell fate and enabling new mechanistic studies. Through careful design of their nanoscale structure, these systems act as biological metamaterials, eliciting unusual biological responses. While predominantly used to interface eukaryotic cells, there is growing interest in non-animal and prokaryotic cell interfacing. Both experimental and theoretical studies have attempted to develop a mechanistic understanding for the observed behaviors, predominantly focusing on the cell – nanostructure interface. Here, we consider how high-aspect-ratio nanostructured surfaces are used to both stimulate and sense biological systems and discuss remaining research questions

Characterizing & modelling the bio-nano interface

The rise of nanotechnology has to led numerous developments in the fields of biotech- nology and medicine. The promise of nanoparticles delivering drugs in vivo and nano- materials peering into cells are highly sought after and currently investigated in research groups around the world. However, despite the potential of such technologies, much is still unknown about the interface between these materials and the biological world. This thesis aims to further our understanding of this interface in order to aid the design of future generations of materials with new and improved functionality. Coarse-grained molecular dynamics simulations were employed to study how nanoporous surfaces can affect model cell membranes in close contact. This modelling showed that curvature can be induced in membranes by fine-tuning nanoporous surfaces leading to preferential local changes in membrane properties and preferential localization of pro- teins. This model was expanded to study in further detail the membrane binding and cur- vature sensing of a key curvature-active protein domain, the Epsin N-Terminal Homology (ENTH) domain. This protein was shown to be able to sense membrane curvature with- out its terminal H0 amphipathic helix both with and without the presence of its key lipid binding partner, phosphatidylinositol 4,5-bisphosphate (PIP2). In addition, another PIP2- binding, curvature-active protein, the AP180 N-Terminal Homology (ANTH) domain, was investigated with this modelling system in order to evaluate the curvature-sensitivity of the domain with three different terminal helix compositions. This domain was shown to have innate curvature sensitivity on neutral membranes. In the presence of PIP2 however, only the fully rigid helix structure allowed for curvature sensing of this protein. In addition to modelling approaches to understand the bio-nano interface, x-ray photo- electron spectroscopy (XPS) was employed to characterize the surfaces of nanostrutured silicon surfaces in order to understand their surface chemistry for biological applications. Gold nanoclusters (AuNCs) were also studied in order to explore the nature of catalytic reactions occurring on their surface.Open Acces

Coarse-Grained Simulations Suggest the Epsin N-Terminal Homology Domain Can Sense Membrane Curvature without Its Terminal Amphipathic Helix

© 2020 American Chemical Society. Nanoscale membrane curvature is a common feature in cell biology required for functions such as endocytosis, exocytosis and cell migration. These processes require the cytoskeleton to exert forces on the membrane to deform it. Cytosolic proteins contain specific motifs which bind to the membrane, connecting it to the internal cytoskeletal machinery. These motifs often bind charged phosphatidylinositol phosphate lipids present in the cell membrane which play significant roles in signaling. These lipids are important for membrane deforming processes, such as endocytosis, but much remains unknown about their role in the sensing of membrane nanocurvature by protein domains. Using coarse-grained molecular dynamics simulations, we investigated the interaction of a model curvature active protein domain, the epsin N-terminal homology domain (ENTH), with curved lipid membranes. The combination of anionic lipids (phosphatidylinositol 4,5-bisphosphate and phosphatidylserine) within the membrane, protein backbone flexibility, and structural changes within the domain were found to affect the domain's ability to sense, bind, and localize with nanoscale precision at curved membrane regions. The findings suggest that the ENTH domain can sense membrane curvature without the presence of its terminal amphipathic α helix via another structural region we have denoted as H3, re-emphasizing the critical relationship between nanoscale membrane curvature and protein function