Protein Scaffold Engineering Towards Tunable Surface Attachment

Solid-Binding Proteins: Bridging Synthesis, Assembly, and Function in Hybrid and Hierarchical Materials Fabrication

There is considerable interest in the development of hybrid organic-inorganic materials because of the potential for harvesting the unique capabilities that each system has to offer. Proteins are an especially attractive organic component owing to the high amount of chemical information encoded in their amino acid sequence, their amenability to molecular and computational (re)design, and the many structures and functions they specify. Genetic installation of solid-binding peptides (SBPs) within protein frameworks affords control over the position and orientation of adhesive and morphogenetic segments, and a path toward predictive synthesis and assembly of functional materials and devices, all while harnessing the built-in properties of the host scaffold. Here, we review the current understanding of the mechanisms through which SBPs bind to technologically relevant interfaces, with an emphasis on the variables that influence the process, and highlight the last decade of progress in the use of solid-binding proteins for hybrid and hierarchical materials synthesis.

In vivo and in vitro protein mediated synthesis of palladium nanoparticles for hydrogenation reactions

We report the biosynthesis of size confined palladium nanoparticles (Pd-NPs). The 2-3 nm size Pd-NPs were grown in 12-mer protein stable protein 1 (SP1), which serves as a template for the NP formation. We further show that by controlling the protein expression levels in the cells we can alter the cells' catalytic activity. The in vivo grown Pd-NPs were utilized in a hydrogenation reaction, converting acetylene feedstock into ethylene and ethane. The presented concept can be further used for a wide range of applications by exploiting the synergetic effect of the biotic elements with the abiotic ones.

Highly ordered protein cage assemblies: A toolkit for new materials

Protein capsids are specialized and versatile natural macromolecules with exceptional properties. Their homogenous, spherical, rod-like or toroidal geometry, and spatially directed functionalities make them intriguing building blocks for self-assembled nanostructures. High degrees of functionality and modifiability allow for their assembly via non-covalent interactions, such as electrostatic and coordination bonding, enabling controlled self-assembly into higher-order structures. These assembly processes are sensitive to the molecules used and the surrounding conditions, making it possible to tune the chemical and physical properties of the resultant material and generate multifunctional and environmentally sensitive systems. These materials have numerous potential applications, including catalysis and drug delivery. This article is categorized under: Biology-Inspired Nanomaterials > Protein and Virus-Based Structures.

Enzyme-Triggered Defined Protein Nanoarrays: Efficient Light-Harvesting Systems to Mimic Chloroplasts

The elegance and efficiency by which chloroplasts harvest solar energy and conduct energy transfer have been a source of inspiration for chemists to mimic such process. However, precise manipulation to obtain orderly arranged antenna chromophores in constructing artificial chloroplast mimics was a great challenge, especially from the structural similarity and bioaffinity standpoints. Here we reported a design strategy that combined covalent and noncovalent interactions to prepare a protein-based light-harvesting system to mimic chloroplasts. Cricoid stable protein one (SP1) was utilized as a building block model. Under enzyme-triggered covalent protein assembly, mutant SP1 with tyrosine (Tyr) residues at the designated sites can couple together to form nanostructures. Through controlling the Tyr sites on the protein surface, we can manipulate the assembly orientation to respectively generate 1D nanotubes and 2D nanosheets. The excellent stability endowed the self-assembled protein architectures with promising applications. We further integrated quantum dots (QDs) possessing optical and electronic properties with the 2D nanosheets to fabricate chloroplast mimics. By attaching different sized QDs as donor and acceptor chromophores to the negatively charged surface of SP1-based protein nanosheets via electrostatic interactions, we successfully developed an artificial light-harvesting system. The assembled protein nanosheets structurally resembled the natural thylakoids, and the QDs can achieve pronounced FRET phenomenon just like the chlorophylls. Therefore, the coassembled system was meaningful to explore the photosynthetic process in vitro, as it was designed to mimic the natural chloroplast.

Monitoring the HIV-1 integrase enzymatic activity using atomic force microscopy in a 2LTR system

Integration of the HIV cDNA into the host chromosome is a key event in the viral replication cycle. It is mediated by the viral integrase (IN) enzyme, which is an attractive anti-HIV drug target. Here we present the first AFM imaging of IN-mediated DNA integration products in a two-LTR system.

Protein nanotubes, channels and cages

Proteins are the work-horses of life and excute the essential processes involved in the growth and repair of cells. These roles include all aspects of cell signalling, metabolism and repair that allow living things to exist. They are not only chemical catalysts and machine components, they are also structural components of the cell or organism, capable of self-organisation into strong supramolecular cages, fibres and meshes. How proteins are encoded genetically and how they are sythesised in vivo is now well understood, and for an increasing number of proteins, the relationship between structure and function is known in exquisite detail. The next challenge in bionanoscience is to adapt useful protein systems to build new functional structures. Well-defined natural structures with potential useful shapes are a good starting point. With this in mind, in this chapter we discuss the properties of natural and artificial protein channels, nanotubes and cages with regard to recent progress and potential future applications. Chemistries for attaching together different proteins to form superstructures are considered as well as the difficulties associated with designing complex protein structures ab initio.

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.

Wiring of redox enzymes on three dimensional self-assembled molecular scaffold

The integration of biological molecules and nanoscale components provides a fertile basis for the construction of hybrid materials of synergic properties and functions. Stable protein 1 (SP1), a highly stable ring shaped protein, was recently used to display different functional domains, to bind nanoparticles (NPs), and to spontaneously form two and three-dimensional structures. Here we show an approach to wire redox enzymes on this self-assembled protein-nanoparticle hybrid. Those hybrids are genetically engineered SP1s, displaying glucose oxidase (GOx) enzymes tethered to the protein inner pore. Moreover, the Au-NP-protein hybrids self-assembled to multiple enzymatic layers on the surface. By wiring the redox enzymes to the electrode, we present an active structure for the bioelectrocatalytic oxidation of glucose. This system demonstrates for the first time a three-dimensional assembly of multiple catalytic modules on a protein scaffold with an efficient electrical wiring of the enzyme units on an electrode surface, thus implementing a hybrid electrically active unit for nanobioelectronic applications.

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.