Showing how peptide sequence dictates code using alphabet soup. Credit Dr Phil Messersmith, University of BerkeleyResearch undertaken at the City University of New York has demonstrated a new way to produce materials that can mimic the properties of melanin, the natural pigment that provides human skin, hair and eyes with their color. A molecular code for melanin-like materials was developed that could offer control over expressing specific properties of the biopolymer, a breakthrough that could lead to new cosmetic, skin care and biomedical applications.
While some biopolymers have a direct connection between their ordered structures and properties, melanin is disordered, hindering attempts to relate its structure to function, a problem for those looking to synthesise its interesting properties, such as protection from UV radiation and free radicals, as well as electronic conductance, adhesiveness and an ability to store energy.
“Perhaps the most surprising property is that we could control the morphology of the polymeric pigments, ranging from soluble spheres for red–brown pigments, to fibers for brown pigments and extended two-dimensional sheets for the dark-brown versions"Rein Ulijn
As reported in Science [Lampel et al. Science (2017) DOI: 10.1126/science.aal5005], the study used simple versions of proteins, that of tripeptides consisting of just three amino acids, to produce different molecular architectures with precisely controlled levels of order and disorder. The team investigated how the amino acid sequence of the tripeptides gave rise to differently ordered architectures, and then used these structures as templates for catalytic oxidation to produce various peptide pigments with useful properties. Subsequent and in-depth characterization also showed that properties – including UV absorbance and nanoscale morphology of the melanin-like materials – could also be controlled by the amino acid sequence of the tripeptide.
With simple peptides being shown to control nanostructure formation at the molecular level, and reorganizing three amino acids in a tripeptide gives rise to differently organized molecular connectivity within the assemblies that form, this allowed the researchers to control the molecular environment in which an amino acid finds itself. Short peptide building blocks with just a few amino acids are therefore versatile components for functional materials and nanostructures, materials that included two-dimensional, sheet-like polymers that demonstrated substantial charge-storage capacity.
As lead researcher Rein Ulijn said “Perhaps the most surprising property is that we could control the morphology of the polymeric pigments, ranging from soluble spheres for red–brown pigments, to fibers for brown pigments and extended two-dimensional sheets for the dark-brown versions".
The team expects short peptides will receive greater attention as tunable, biodegradable and highly versatile materials, and are investigating further the chemical structures that form to expand the resulting functionalities and properties of the melanin-like materials they produce, as well as sequence space and other functions beyond controlled assembly and oxidation.