Float and compress: honeycomb-like array of a highly stable protein scaffold

Protein Assembly by Design

Proteins are nature's primary building blocks for the construction of sophisticated molecular machines and dynamic materials, ranging from protein complexes such as photosystem II and nitrogenase that drive biogeochemical cycles to cytoskeletal assemblies and muscle fibers for motion. Such natural systems have inspired extensive efforts in the rational design of artificial protein assemblies in the last two decades. As molecular building blocks, proteins are highly complex, in terms of both their three-dimensional structures and chemical compositions. To enable control over the self-assembly of such complex molecules, scientists have devised many creative strategies by combining tools and principles of experimental and computational biophysics, supramolecular chemistry, inorganic chemistry, materials science, and polymer chemistry, among others. Owing to these innovative strategies, what started as a purely structure-building exercise two decades ago has, in short order, led to artificial protein assemblies with unprecedented structures and functions and protein-based materials with unusual properties. Our goal in this review is to give an overview of this exciting and highly interdisciplinary area of research, first outlining the design strategies and tools that have been devised for controlling protein self-assembly, then describing the diverse structures of artificial protein assemblies, and finally highlighting the emergent properties and functions of these assemblies.

Clues for biomimetics from natural composite materials

Bio-inspired material systems are derived from different living organisms such as plants, arthropods, mammals and marine organisms. These biomaterial systems from nature are always present in the form of composites, with molecular-scale interactions optimized to direct functional features. With interest in replacing synthetic materials with natural materials due to biocompatibility, sustainability and green chemistry issues, it is important to understand the molecular structure and chemistry of the raw component materials to also learn from their natural engineering, interfaces and interactions leading to durable and highly functional material architectures. This review will focus on applications of biomaterials in single material forms, as well as biomimetic composites inspired by natural organizational features. Examples of different natural composite systems will be described, followed by implementation of the principles underlying their composite organization into artificial bio-inspired systems for materials with new functional features for future medicine.

Properties of β-sitostanol/DPPC monolayers studied with Grazing Incidence X-ray Diffraction (GIXD) and Brewster Angle Microscopy

Although the influence of structurally modified sterols on artificial membranes has been intensively investigated, studies on the properties of stanols, which are saturated analogs of sterols, are very rare. Therefore, we have performed Grazing Incidence X-ray Diffraction (GIXD) experiments aimed at studying in-plane organization of a plant stanol-β-sitostanol monolayer and its mixtures with 1,2-dipalmitoyl-sn-glycero-3-phosphocholine - DPPC at the air/water interface. The collected GIXD data, resulting in-plane parameters and BAM images provide information on molecular organization and in-plane ordering of the investigated films. It was found that the lateral organization of β-sitostanol/DPPC monolayers depends on their composition. The oblique structure of the in-plane lattice of tilted hydrophobic region of molecules, found for DPPC film, is maintained at 10 mol% of stanol in the system. However, at 30 and 90 mol% of stanol in the mixture, the arrangement of molecules is hexagonal and they are oriented perpendicularly to the interface. With the addition of stanol the extend of the in-plane order of the monolayers decreases. Moreover, in mixtures the ordered domains consist of both monolayer's components. Additionally, β-sitostanol film is of similar in-plane organization as the corresponding sterol monolayer (β-sitosterol) and stanol induces condensing effect on DPPC.

Amyloid-beta fibrillogenesis seeded by interface-induced peptide misfolding and self-assembly

The amphipathicity of the natively unstructured amyloid-beta (Abeta40) peptide may play an important role in its aggregation into beta-sheet rich fibrils, which is linked to the pathogenesis of Alzheimer's disease. Using the air/subphase interface as a model interface, we characterized Abeta's surface activity and its conformation, assembly, and morphology at the interface. Abeta readily adsorbed to the air/subphase interface to form a 20 A thick film and showed a critical micelle concentration of approximately 120 nM. Abeta adsorbed at the air/subphase exhibited in-plane ordering that gave rise to Bragg peaks in grazing-incidence x-ray diffraction measurements. Analysis of the peaks showed that the air/subphase interface induced Abeta to fold into a beta-sheet conformation and to self-assemble into approximately 100 A-sized ordered clusters. The formation of these clusters at the air/subphase interface was not affected by pH, salts, or the presence of sucrose or urea, which are known to stabilize or denature native proteins, suggesting that interface-driven Abeta misfolding and assembly are strongly favored. Furthermore, Abeta at the interface seeded the growth of fibrils in the bulk with a distinct morphology compared to those formed by homogeneous nucleation. Our results indicate that interface-induced Abeta misfolding may serve as a heterogeneous, nucleation-controlled aggregation mechanism for Abeta fibrillogenesis in vivo.

Logic implementations using a single nanoparticle-protein hybrid

A Set-Reset machine is the simplest logic circuit with a built-in memory. Its output is a (nonlinear) function of the input and of the state stored in the machine's memory. Here, we report a nanoscale Set-Reset machine operating at room temperature that is based on a 5-nm silicon nanoparticle attached to the inner pore of a stable circular protein. The nanoparticle-protein hybrid can also function as a balanced ternary multiplier. Conductive atomic force microscopy is used to implement the logic input and output operations, and the processing of the logic Set and Reset operations relies on the finite capacitance of the nanoparticle provided by the good electrical isolation given by the protein, thus enabling stability of the logic device states. We show that the machine can be cycled, such that in every successive cycle, the previous state in the memory is retained as the present state. The energy cost of one cycle of computation is minimized to the cost of charging this state.