Associate Professor University of Houston Houston, Texas, United States
Introduction: : α-helices and β-sheets are the 2 primarily occurring protein secondary structures that govern biology. The latter is typically composed of amino acids that associate through supramolecular (non-covalent H-bonds, van der Waal’s, electrostatic) interactions. Β-sheets typically form between (designer) hairpin like regions of peptides/ proteins or regions that form complementary supramolecular bonds. Prior work on SAPs that form parallel and anti-parallel dimers, and laterally self-assembly perpendicular to the axis of dimerization have been extensively described in the literature. Here we present the development of a novel β-sheet secondary structure – a β-brickwork composed of a single self-complimentary peptide.
Materials and
Methods: : We have computationally designed a putative octapeptide based on the sequence requirement: linear organization of pi stacking, amphiphilic interactions, salt-bridges - to potentiate β-brickwork assembly.
These octapeptides exhibit robust self-assembly into linear nanofibers that entangle into hydrogels, with a diverse set of supramolecular bond types within each repeat brick subunit. These 8-peptide building blocks stack in a 2-layer thick peptide brickwork – binding to intrinsic, yet specific, staggered self-binding domains (pi-pi stacking, hydrophilic/hydrophobic amphiphilic interactions, oppositely charged salt bridges) of linearly staggered bricks. Interestingly, this showed a β-sheet structure in circular dichroism and FTIR – representing the first report of a novel β-sheet brickwork assembly – composed of β-bricks.
Peptide design was assisted by Rosetta and VMD.. Peptide purity was measured with HPLC and identity by ESI-MS. Peptide secondary structure was analyzed by FTIR and CD. Peptide mechanics and ultrastructure was studied by oscillatory rheometry, AFM, SEM and TEM. Peptide in vivo biocompatibility was measured by sub-q bolus compatibility evaluation and FACS quantification of cellular infiltrate.
Results, Conclusions, and Discussions:: In both nature and bioinspired designs, this is the first report of a β-sheet forming linear fibers where the plan of β-sheet formation is parallel to the direction of fibrillation, especially for such a short (octa-)peptide. Aside from the scientific novelty, these β-sheets represent a new class of self-assemblies that have not been seen by the immune system or other enzymatic processes. This presents a potential platform, whereby highly self-adhesive fiber forming monomers (optimized through our ML algorithm) can be generated for tailorable applications from surgical glues, to tissue engineering scaffolds for soft and hard tissue engineering, 3D printed gels for in vitro/ in vivo applications, optimization of biomolecules or bioenzymatic catalysis owing to bioactive domains localized in/on a nanofibrous matrix, and a host of other applications. Further, they may have unique in vivo responses – recruitment of various cells types atypical to other β-sheets frameworks – including the disparities seen with current β-amyloid stability vs β-sheet SAP with similar assembly mechanisms that we have engineered degrading in 3-4 weeks. Similar to the first generation SAP hydrogels we and others have extensively characterized, we expect these thixotropic supramolular hydrogels to rapidly infiltrate with cells and degrade (tunably) in vivo. Specifically, we envision unique classes of immune (neutrophil, monocyte (polarization), T cell), endothelial / mesenchymal cells infiltration characteristic of this new assembly type, and amino acid composition of β-bricks. We may perhaps see that adaptive (B cell) driven antibody responses are muted to this heretofore β-brick assembly – alternatively we may see an enhanced IgG (or potentially other immunoglobulin) response characteristic to these assemblies providing opportunities for both immune (stealth) or self-adjuvanting/ immune cell reservoir biomaterials development. From an intellectual property perspective, much of the IP for SAP is 10-20 years old, with products and infrastructure (along with knowledge on the benefits / utility of SAP) coming to the fore only in the last 3-5 years. The time is ripe for a new peptide based biomaterial, especially of a class that is novel and distinct to date.
Acknowledgements and/or References (Optional):: NOTE: we are filing IP and therefore will present data at the conference.
