Construction of a Chassis for a Tripartite Protein-Based Molecular Motor

Coiled Coil Peptide Tiles (CCPTs): Expanding the Peptide Building Block Design with Multivalent Peptide Macrocycles

Owing to their synthetic accessibility and protein-mimetic features, peptides represent an attractive biomolecular building block for the fabrication of artificial biomimetic materials with emergent properties and functions. Here, we expand the peptide building block design space through unveiling the design, synthesis, and characterization of novel, multivalent peptide macrocycles (96mers), termed coiled coil peptide tiles (CCPTs). CCPTs comprise multiple orthogonal coiled coil peptide domains that are separated by flexible linkers. The constraints, imposed by cyclization, confer CCPTs with the ability to direct programmable, multidirectional interactions between coiled coil-forming "edge" domains of CCPTs and their free peptide binding partners. These fully synthetic constructs are assembled using a convergent synthetic strategy via a combination of native chemical ligation and Sortase A-mediated cyclization. Circular dichroism (CD) studies reveal the increased helical stability associated with cyclization and subsequent coiled coil formation along the CCPT edges. Size-exclusion chromatography (SEC), analytical high-performance liquid chromatography (HPLC), and fluorescence quenching assays provide a comprehensive biophysical characterization of various assembled CCPT complexes and confirm the orthogonal colocalization between coiled coil domains within CCPTs and their designed on-target free peptide partners. Lastly, we employ molecular dynamics (MD) simulations, which provide molecular-level insights into experimental results, as a supporting method for understanding the structural dynamics of CCPTs and their complexes. MD analysis of the simulated CCPT architectures reveals the rigidification and expansion of CCPTs upon complexation, i.e., coiled coil formation with their designed binding partners, and provides insights for guiding the designs of future generations of CCPTs. The addition of CCPTs into the repertoire of coiled coil-based building blocks has the potential for expanding the coiled coil assembly landscape by unlocking new topologies having designable intermolecular interfaces.

Understanding a protein fold: the physics, chemistry, and biology of α-helical coiled coils

Protein science is being transformed by powerful computational methods for structure prediction and design: AlphaFold2 can predict many natural protein structures from sequence, and other AI methods are enabling the de novo design of new structures. This raises a question: how much do we understand the underlying sequence-to-structure/function relationships being captured by these methods? This perspective presents our current understanding of one class of protein assembly, the α-helical coiled coils. At first sight, these are straightforward: sequence repeats of hydrophobic (h) and polar (p) residues, (hpphppp)_n, direct the folding and assembly of amphipathic α helices into bundles. However, many different bundles are possible: they can have two or more helices (different oligomers); the helices can have parallel, antiparallel or mixed arrangements (different topologies); and the helical sequences can be the same (homomers) or different (heteromers). Thus, sequence-to-structure relationships must be present within the hpphppp repeats to distinguish these states. I discuss the current understanding of this problem at three levels: First, physics gives a parametric framework to generate the many possible coiled-coil backbone structures. Second, chemistry provides a means to explore and deliver sequence-to-structure relationships. Third, biology shows how coiled coils are adapted and functionalized in nature, inspiring applications of coiled coils in synthetic biology. I argue that the chemistry is largely understood; the physics is partly solved, though the considerable challenge of predicting even relative stabilities of different coiled-coil states remains; but there is much more to explore in the biology and synthetic biology of coiled coils.

Through the Eyes of Creators: Observing Artificial Molecular Motors

Inspired by molecular motors in biology, there has been significant progress in building artificial molecular motors, using a number of quite distinct approaches. As the constructs become more sophisticated, there is also an increasing need to directly observe the motion of artificial motors at the nanoscale and to characterize their performance. Here, we review the most used methods that tackle those tasks. We aim to help experimentalists with an overview of the available tools used for different types of synthetic motors and to choose the method most suited for the size of a motor and the desired measurements, such as the generated force or distances in the moving system. Furthermore, for many envisioned applications of synthetic motors, it will be a requirement to guide and control directed motions. We therefore also provide a perspective on how motors can be observed on structures that allow for directional guidance, such as nanowires and microchannels. Thus, this Review facilitates the future research on synthetic molecular motors, where observations at a single-motor level and a detailed characterization of motion will promote applications.

Self-assembly and regulation of protein cages from pre-organised coiled-coil modules

Coiled-coil protein origami (CCPO) is a modular strategy for the de novo design of polypeptide nanostructures. CCPO folds are defined by the sequential order of concatenated orthogonal coiled-coil (CC) dimer-forming peptides, where a single-chain protein is programmed to fold into a polyhedral cage. Self-assembly of CC-based nanostructures from several chains, similarly as in DNA nanotechnology, could facilitate the design of more complex assemblies and the introduction of functionalities. Here, we show the design of a de novo triangular bipyramid fold comprising 18 CC-forming segments and define the strategy for the two-chain self-assembly of the bipyramidal cage from asymmetric and pseudo-symmetric pre-organised structural modules. In addition, by introducing a protease cleavage site and masking the interfacial CC-forming segments in the two-chain bipyramidal cage, we devise a proteolysis-mediated conformational switch. This strategy could be extended to other modular protein folds, facilitating the construction of dynamic multi-chain CC-based complexes.

Coiled-coil protein origami is a strategy for the de novo design of polypeptide nanostructures based on coiled-coil dimer forming peptides, where a single chain protein folds into a polyhedral cage. Here, the authors design a single-chain triangular bipyramid and also demonstrate that the bipyramid can be self-assembled as a heterodimeric complex, comprising pre-defined subunits.

Design of novel protein building modules and modular architectures

Nature uses only a limited number of protein topologies and while several folds have evolved independently over time, there are clearly many possible topologies that have not been explored by evolution. With recent advances of protein design concepts, computational modeling tools, high resolution and high-throughput experimental methods it is now possible to design new protein architectures. The collection of building blocks and design principles widened both in size and complexity, offering an expanded toolset for building new modular folds and functional protein structures. Here we review and discuss recent achievements of protein design, focusing in particular on the use and prospects of modular approaches for assembling new protein folds.

Artificial coiled coil biomineralisation protein for the synthesis of magnetic nanoparticles

Green synthesis of precise inorganic nanomaterials is a major challenge. Magnetotactic bacteria biomineralise magnetite nanoparticles (MNPs) within membrane vesicles (magnetosomes), which are embedded with dedicated proteins that control nanocrystal formation. Some such proteins are used in vitro to control MNP formation in green synthesis; however, these membrane proteins self-aggregate, making their production and use in vitro challenging and difficult to scale. Here, we provide an alternative solution by displaying active loops from biomineralisation proteins Mms13 and MmsF on stem-loop coiled-coil scaffold proteins (Mms13cc/MmsFcc). These artificial biomineralisation proteins form soluble, stable alpha-helical hairpin monomers, and MmsFcc successfully controls the formation of MNP when added to magnetite synthesis, regulating synthesis comparably to native MmsF. This study demonstrates how displaying active loops from membrane proteins on coiled-coil scaffolds removes membrane protein solubility issues, while retains activity, enabling a generic approach to readily-expressible, versatile, artificial membrane proteins for more accessible study and exploitation.

Proteins have been used in the synthesis of magnetic nanoparticles but issues with aggregation limit this application. Here, the authors report on the synthesis of coiled proteins that display the active loop of the natural proteins to avoid aggregation and investigate the application in nanoparticle synthesis.

SwitCCh: Metal-Site Design for Controlling the Assembly of a Coiled-Coil Homodimer

Conformational change of proteins in response to chemical or physical signals is the underlying principle of many regulatory and transport mechanisms in biological systems. The ability to design proteins the conformational state of which can be precisely and reversibly controlled would facilitate the development of molecular machines tailored for specific applications. Here we explore metal-binding site design to engineer a peptide-based conformational switch called SwitCCh that assembles into a homodimeric coiled-coil in response to the addition of Zn^II ions or low pH. Addition of Zn^II promoted formation of a parallel homodimer with an increase in thermal stability by more than 30 °C. The peptide could be reversibly cycled between the coiled-coil and random conformation. Furthermore, the SwitCCh peptide was orthogonal to the previously developed coiled-coil dimer set, indicating it could be used for regulated self-assembly of coiled-coil based nanostructures and materials.

Assembly of Multicomponent Protein Filaments Using Engineered Subunit Interfaces

Exploiting the ability of proteins to self-assemble into architectural templates may provide novel routes for the positioning of functional molecules in nanotechnology. Here we report the engineering of multicomponent protein templates composed of distinct monomers that assemble in repeating orders into a dynamic functional structure. This was achieved by redesigning the protein-protein interfaces of a molecular chaperone with helical sequences to create unique subunits that assemble through orthogonal coiled-coils into filaments up to several hundred nanometers in length. Subsequently, it was demonstrated that functional proteins could be fused to the subunits to achieve ordered alignment along filaments. Importantly, the multicomponent filaments had molecular chaperone activity and could prevent other proteins from thermal-induced aggregation, a potentially useful property for the scaffolding of enzymes. The design in this work is presented as proof-of-concept for the creation of modular templates that could potentially be used to position functional molecules, stabilize other proteins such as enzymes, and enable controlled assembly of nanostructures with unique topologies.

Coiled coil protein origami: from modular design principles towards biotechnological applications

This review illustrates the current state in designing coiled-coil-based proteins with an emphasis on coiled coil protein origami structures and their potential.