Lisa M. Carrick

Self-assembling β-Sheet Tape Forming Peptides

Biological proteins have intrinsically the ability to self-assemble, and this has been implicated in pathological situations called amyloid diseases. Conversely understanding protein self-assembly and how to control it can open up the route to new nanodevices and nanostructured materials for a wide range of applications in medicine, chemical industry and nanotechnology. Biological peptides and proteins have complex chemical structure and conformation. This makes it difficult to decipher the fundamental principles that drive their self-assembling behaviours. Here we review our work on the self-assembly of simple de novo peptides in solution. These peptides are designed so that: (i) the chemical complexity of the primary structure and (ii) the conformational complexity are both kept to a minimum. Each peptide adopts an extended β-strand conformation in solution and these β-strands self-assemble in one dimension to form elongated tapes as well as higher order aggregates with pure antiparallel β-sheet structure, without the presence of any other conformations such as turns, loops, α-helices or random coils. Experimental data of the self-assembling properties are fitted with an appropriate theoretical model to build a quantitative relationship between peptide primary structure and self-assembly. These simple systems provide us with the opportunity to reveal the generic properties of the pure β-sheet structures and expose the underlying physicochemical principles that drive the self-assembling behaviour of this biological motif.

De novo designed positively charged tape-forming peptides: self-assembly and gelation in physiological solutions and their evaluation as 3D matrices for cell growth

Learning to control self-assembling nanostructures is currently one of the biggest challenges and promises in nanoscale science and nanotechnology. Nanostructured 3D matrices in particular are considered essential components in tissue engineering and regenerative medicine, e.g. as multifunctional scaffolds for cell encapsulation, growth and differentiation. Self-assembling peptide gels are a promising novel class of matrices for tissue engineering. Recently a new versatile family of negatively or positively charged tape-forming peptides have been de novo designed. These peptides were all found to self-assemble into nanostructured networks and gel cell transport medium in a simple, consistent and reproducible manner. Here we focus on the positively charged peptides of this family. We systematically changed the peptide to be amphiphilic or completely polar, or to be based on different polar uncharged amino acids (glutamine, serine, asparagine or threonine). The peptides were sterilised by γ-irradiation and were all found to be biocompatible using the contact cytotoxicity test. L929 murine fibroblast cells were encapsulated in 3D cell cultures inside 2% w/v gels and their proliferation was measured after 14 days using the ATP Lite assay. In this way a structure–function activity was established. Trifluoroacetic acid present in the peptide from the purification step was found to have a negative effect on cell proliferation. Peptide self-assembly in physiological conditions was studied extensively using spectroscopic and microscopic techniques, allowing rationalization of the observed biological structure–function activity. This detailed and systematic study enables us to develop refined criteria for the design of positively charged tape forming peptides and gels for biological and medical applications.

Peptide strand length controls the energetics of self-assembly and morphology of β-sheet fibrils

Self‐assembling peptides can be used as versatile, natural, and multifunctional building blocks to produce a variety of well‐defined nanostructures, materials and devices for applications in medicine and nanotechnology. Here, we concentrate on the 1D self‐assembly of de novo designed Px‐2 peptide β‐strands into anti‐parallel β‐sheet tapes and higher order aggregates. We study six members of the Px‐2 family, ranging from 3 amino acids (aa) to 13 aa in length, using a range of complementary experimental techniques, computer simulation and theoretical statistical mechanics. The critical concentration for self‐assembly (c*) is found to increase systematically with decreasing peptide length. The shortest peptide found to self‐assemble into soluble β‐tapes in water is a 5 amino acid residue peptide. These investigations help decipher the role of the peptide length in controlling self‐assembly, aggregate morphology, and material properties. By extracting free energies from these data using a statistical mechanical analysis and combining the results with computer simulations at the atomistic level, we can extract the entropy of association for individual β‐strands.