Chun-Long Chen, Pacific Northwest National Laboratory
Nico Sommerdijk, Eindhoven University of Technology
Tiffany Walsh, Deakin University
Shuguang Zhang, Massachusetts Institute of Technology
Pacific Northwest National Laboratory
BM09.01: Biomimetic Materials Based on Peptide Self-Assembly
Monday AM, November 26, 2018
Sheraton, 2nd Floor, Back Bay A
8:00 AM - BM09.01.01
Self-Organization of Peptides in Bioinspired Vesicles—Role of Relative Concentration and Helical Separation
Akash Banerjee1,Meenakshi Dutt1
Rutgers University1Show Abstract
Biological cells can inspire the creation of nanoparticles equipped to store and release hydrophobic drug molecules upon demand. Lipid vesicles impregnated with alpha-helical peptides have demonstrated the clustering of the peptides under equilibrium. The formation of thick, amphiphilic, transmembrane channels via the self-organization of the peptides could be potentially used for the on-demand release of small drug molecules from the hydrophobic core of a vesicle bilayer. We are interested in understanding the driving forces responsible for cluster formations and evaluating their effects using the Molecular Dynamics simulation technique. Coarse grained representations of the molecules are used to resolve the extended spatiotemporal scales relevant to the problem at hand. The bonded and non-bonded interactions between the particles is captured by the Martini force field. We investigate the role of peptide concentration and helical separation on the cluster formation. We find the cluster size to be dependent more on helical separation as compared to peptide concentration. Additionally, we test the role of hydrophobic mismatch to understand the effect of electrostatic interactions between the peptides and lipid molecules. Our results demonstrate negative mismatch to result in larger cluster sizes as compared to a zero hydrophobic mismatch condition due to larger perturbations in the vesicle monolayers.
8:15 AM - BM09.01.02
Self-Assembly of Membrane-Active Peptides into Macromolecular-Size Pores
Kalina Hristova1,Sijia Li1,Sarah Kim1,Anna Pittman2,Gavin King2,William Wimley3
Johns Hopkins University1,University of Missouri2,Tulane University3Show Abstract
Peptides that self-assemble into pore-like structures in lipid bilayers could have utility in a variety of biotechnological and clinical applications due to their ability to breach the barrier imposed by lipid bilayers. To empower such discoveries, we use rationally designed peptide libraries and high-throughput screens to select peptides based on a particular property, in this case macromolecular-size bilayer poration. Towards this goal, we designed a library based on the bee venom peptide melittin, and we developed a high throughput screen that reports on the passage of macromolecules across lipid bilayers. We identified two peptide families that efficiently assemble into large pore-like structures. One of the families is highly active at pH 7. The other peptide family is pH sensitive, as its self-assembly is triggered by low pH. The pH-triggered peptides could be used for endosomal release of uptaken polar molecules into the cell cytosol, upon endosomal acidification. They also could be used in cancer therapies to selectively permeabilize the plasma membranes of cancer cells, since the vicinity of solid tumors is often acidic. Additional generations can be screened to further fine-tune the properties of these peptides.
8:30 AM - BM09.01.03
Exploring the Tubability of the Aggregation and Gelation Process of the Tripeptide Glycyl-Alanyl-Glycine (GAG)
David DiGuiseppi1,Lavenia Thursch1,Nicolas Alvarez1,Reinhard Schweitzer-Stenner1
Drexel University1Show Abstract
Self-assembly of biomolecules is a prominent issue explored in biomedical, biophysical, and bio-material research. Understanding how and why certain peptides/proteins prefer to self-assemble into larger networks can reveal the mechanism of amyloid formation and assist in bottom-up designs of supramolecular structures like gels and nanotubes. Some low molecular weight di- or tripeptides with aromatic residues and terminal groups have been shown to form gels. Contrary to expectations, we recently discovered that cationic glycylalanylglycine (GAG), a tripeptide of low hydrophobicity, forms a gel in 55 mol% ethanol/45 mol% water at room temperature if the concentration exceeds 200 mM. The underlying structure is comprised of unusually long crystalline fibrils (in the 10-5m range), which do not exhibit the canonical β-sheet structure. Rheological data and vibrational circular dichroism spectra suggest the existence of two different gel phases, one formed between 15° and 35°C with left handed twisted fibrils and G’ values at ca. 2*104 Pa and another one formed below 15°C with right handed twisted fibrils and G’ values close to 105 Pa. Results from DFT calculations indicate that the two phases might be underlied by rather differently structured fibrils. The fluorescence kinetics probing the incorporation of thioflavin T into the hydrophobic interior of fibrils indicate a retarded diffusion of the fluorophore into fibrils that formed rather quickly after incubation above 15°C, while fluorescence increase, and gelation proceed on a similar time scale for the gel phase formed below this temperature. Upon increasing the temperature, it can preserve this capability until the melting temperature is reached, which suggests that this gel phase has all what it takes to function as a drug delivery system. The potential reformation process of the fibrils probed by UVCD, rheology, and microscopy show that after sitting for 16h above the melting temperature, the fibrils do not have the ability to grow back. Instead, microscopic images suggest the formation of a crystal-type structure that forms in its place. Our results therefore suggest that the gel phases are meta-stable states of the system that form more quickly at or below room temperature. We care currently working on optimizing the gelation/melting conditions for specific biotechnological applications of the gel as well as characterizing the observed crystal-type structure.
8:45 AM - BM09.01.04
Neutral Self-Assembling Multidomain Peptides—Steric Impediment Regulates Nanofiber Formation and Materials Properties
Tania Lopez Silva1,David Leach1,I-Che Li1,Xinran Wang1,Jeffrey Hartgerink1
Rice University1Show Abstract
Peptide-based materials have drawn high interest for their use in biomedical applications such as drug delivery, cell encapsulation, and tissue regeneration. Particularly, self-assembling peptide hydrogels have shown promising properties as biomaterials since their properties and functionality are tunable by their peptide sequence. For example, they are inherently biocompatible and biodegradable, their nanofibrous structure resembles the extracellular matrix, and they form materials with high-water content. Generally, these peptides utilize ionic amino acids to control self-assembly by changing the pH or ionic strength. Included in these group are the self-assembling Multidomain Peptide nanofibers (MDP), composed of an amphiphilic β-sheet forming core and flanking charged domains, which increase peptide solubility and make the peptide material responsive to pH changes and the presence of ions.
It is known that the biological response and cell behavior is highly dependent on the chemistry of the materials. Positive polymers promote cell adhesion and proliferation while showing concentration-dependent cytotoxicity, whereas neutral polymers, such as PEG, are frequently inert, biocompatible and non-immunogenic. Previously, all MDPs were either positively or negatively charged; therefore, expanding the scope of MDPs to neutral, non-ionic peptides will make distinct biological properties available that are not present in highly charged peptides.
Strategies to control the self-assembly of non-ionic peptides is limited because these peptides tend to have low solubility, aggregate or precipitate in aqueous solutions, making the formation of finite supramolecular structures and self-assembled hydrogels challenging. In this project, we present an alternative mechanism to control the self-assembly of neutral, uncharged multidomain peptides by utilizing steric impediment. Through the study of a series of neutral peptides, we analyzed the effect of the steric interactions on the peptide solubility, aggregation, nanostructure, and hydrogelation. From the series, a novel neutral multidomain peptide hydrogel was developed, which is inert to pH variation and ionic strength. This novel material showed promising properties for biomedical, cell preservation and tissue regeneration applications.
9:00 AM - BM09.01.05
Self-Assembly of 2D Peptide-Based Crystalline Nanomaterials
Emory University1Show Abstract
Structurally defined materials on the nanometer length-scale have been historically the most challenging to rationally construct and the most difficult to structurally analyze. Sequence-specific biomolecules, i.e., proteins and nucleic acids, have advantages as design elements for construction of these types of nano-scale materials in that correlations can be drawn between sequence and higher order structure, potentially affording ordered assemblies in which functional properties can be controlled through the progression of structural hierarchy encoded at the molecular level. The predictable design of self-assembled structures requires precise structural control of the interfaces between peptide subunits (protomers). However, control of quaternary structure has proven to be challenging to reliably predict, as conservative changes in sequence can result in significant changes in higher order, i.e., supramolecular, structure. We have employed simple self-assembling peptides as building blocks for the construction of two-dimensional nano-scale assemblies. In contrast to filamentous assemblies (e.g., fibrils, ribbons, and tubes), protein-based two-dimensional assemblies occur relatively infrequently in native biological systems. We have demonstrated that extended and structurally defined two-dimensional assemblies can be constructed through lateral association of chiral rod-like subunits such as the collagen triple helix. The resultant assemblies can exhibit sequence-dependent control of structure, including growth in the lateral and/or axial dimensions. Moreover, the sheet-like assemblies can be integrated with other self-assembled biological structural motifs, such as DNA origami nano-tiles, to afford self-organized hybrid assemblies. Despite the potential for these two-dimensional assemblies as structurally defined nano-scale scaffolds, it remains challenging to reliably predict and control the structure of the assemblies based on sequence-structure correlations at present.
10:00 AM - BM09.01.06
Bio-Inspired Materials Linking Covalent and Supramolecular Polymers
Northwestern University1Show Abstract
Supramolecular soft matter is a rapidly emerging field that encompasses the rational use of organic molecules to design function in materials. The most promising systems are “supramolecular polymers” since one-dimensional catenation of structural units is a critical feature to create mechanically robust macroscopic systems and directed transport of charge in aligned morphologies. Supramolecular polymers, in contrast to macromolecules in which structural units are linked through covalent bonds, supramolecular systems are designed using additive noncovalent bonds that are tunable over a very broad range of binding energies encoded in the molecular structure of the “mers”. Furthermore, a major gap in the design of synthetic soft matter is the rational integration of covalent and supramolecular polymers, a concept that is used to craft function in the structures of living organisms. This lecture will describe first entirely supramolecular systems based on peptides and nucleic acids in which dynamics of non-covalently bonded monomers can reversibly form superstructures linked to mechanical and biological functions. Within the domain of hybrid systems in which covalent macromolecules are integrated with supramolecular structures, the lecture will describe materials inspired by muscles that are capable of transducing thermal to mechanical energy, light to mechanical energy, and light to chemical energy in photocatalytic materials.
10:30 AM - BM09.01.07
Self-Assembly of Hierarchical Cellular Materials from Amphiphic Triblock Peptides
Erik Spoerke1,Brad Jones1,Jill Wheeler1,Jeffrey Vervacke1,Christina Ting1,Mark Stevens1
Sandia National Laboratories1Show Abstract
Macromolecular self-assembly in biological systems takes many forms and enables countless functions across multiple length scales. Often, the structure and function of these assembled structures are dictated by subtle changes in the composition of the molecular building blocks that make up these materials. For example, simple amino acid substitutions can impart significant changes in the structure and function of protein assemblies. Inspired by this theme, we explore here the self-assembly of an ABC triblock peptide-oligoethylene oxide amphiphile with hydrophilic A and C blocks and a hydrophobic B peptide block. By varying the amino acid side chain size and hydrophobicity within the B-block, we observe aqueous self-assembly into polymorphic cellular particles with hierarchical structure and porosity ranging from giant vesicles with foam-like membranes to porous tubular architectures. These structures are characterized microscopically and spectroscopically to determine the relationships between the varied peptide compositions, tunable intermolecular interactions, and the observed morphologies. Additional evaluation of these materials as vehicles for molecular encapsulation and as templates for secondary mineral templating reveal potential new strategies to control hierarchical materials synthesis and assembly through bio-inspired molecular building block design.
Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.
10:45 AM - BM09.01.08
Modular Peptide-Polymer Conjugates—A Platform Technology for Mucin Analogues
Daniel French1,Luis Navarro1,Stefan Zauscher1
Duke Univ1Show Abstract
Mucins – the glycoprotein building-blocks of mucus – play diverse and crucial roles in the body. These functions range from lubrication of articular joints and the eye, to the protection of stomach endothelium from the harsh environment of the lumen, to modulation of microflora populations in the digestive and respiratory systems. Despite this diversity, these functions are all attributed to slight modifications in a general structure shared by all mucins: a telechelic triblock polypeptide comprised of terminal association moieties and a heavily glycosylated core which forms a hydrated bottle brush center. In vivo, these versatile functions are achieved by altering glycosylation patterns, crosslinking density, and targeting affinity in a modular fashion.
Inspired by this adaptability, we have emulated this general architecture in a modular conjugate analogue mucin platform which engenders general structural features preserved among mucins which we, and others, have identified as key to their function. To recapitulate the mucin backbone, we genetically tether and co-express terminal binding modules with a lysine-rich, elastin-like polypeptide (ELP) central scaffold. Binding modules may include sequences designed to target surfaces of interest, to facilitate intramolecular associations, or to direct surface conformation of our construct. The regularly-spaced lysines in the ELP scaffold can be harnessed for grafting synthetic polymer bristles. Bristle chemistry may be chosen for a desired property (including non-fouling character and lubricity) independent of the binding and scaffold modules. Our platform is, to our knowledge, the first to adapt the modularity of the mucin architecture into a bio-synthetic platform technology.
To demonstrate the application of our platform to clinically-relevant problems, we have tailored our mCAMP to osteoarthritis and kidney stone disease, two conditions infamous for profound morbidity and high prevalence. In tailoring our analogue mucin to cartilage, we hope to rival the performance of lubricin, a natural mucin which provides lubrication and wear protection to articular joints. Moreover, we seek to harness the properties of natural mucins and apply them to systems not naturally protected by mucinous coatings. In doing so, we have ad