Melanin production by tyrosinase activity on a tyrosine-rich peptide fragment and pH-dependent self-assembly of its lipidated analogue.

We investigate the self-assembly of a palmitoylated (C16-chain at the N terminus) peptide fragment in comparison to the unlipidated peptide EELNRYY, a fragment of the gut hormone peptide PYY3-36. The lipopeptide C16-EELNRYY shows remarkable pH-dependent self-assembly above measured critical aggregation concentrations, forming fibrils at pH 7, but micelles at pH 10. The parent peptide does not show self-assembly behaviour. The lipopeptide forms hydrogels at sufficiently high concentration at pH 7, the dynamic mechanical properties of which were measured. We also show that the tyrosine functionality at the C terminus of EELNRYY can be used to enzymatically produce the pigment melanin. The enzyme tyrosinase oxidises tyrosine into 3,4-dihydroxyphenylalanine (DOPA), DOPA-quinone and further products, eventually forming eumelanin. This is a mechanism of photo-protection in the skin, for this reason controlling tyrosinase activity is a major target for skin care applications and EELNRYY has potential to be developed for such uses.

Self-Assembly of Lipopeptides Containing Short Peptide Fragments Derived from the Gastrointestinal Hormone PYY3-36: From Micelles to Amyloid Fibrils.

We investigate the impact of lipidation on the self-assembly of two peptide fragments from the gastrointestinal peptide hormone PYY3-36. The lipopeptides C16IKPEAP and C16IKPEAPGE contain the first 6 and 8 amino acid residues, respectively, from the PYY3-36 peptide sequence, with a palmitoyl C16 tail attached at the N-terminus. These lipopeptides form spherical micelles in aqueous solution, above a critical micelle concentration (cmc), which is pH-dependent. Modeling of small-angle X-ray scattering data along with molecular dynamics simulations shows the formation of micelles with a hydrophobic interior and a well-hydrated exterior. The lipopeptides have a disordered conformation over the pH and temperature ranges studied. The cmc is found to be independent of temperature, pointing to athermal micellization. In contrast to the presence of hydrated micelles in solution, ß-sheet amyloid fibrils form in dried samples. Thus, the nanostructure of lipidated PYY3-36 fragment peptides can be tuned by control of pH or concentration, for future applications.

The Effect of Lipidation on the Self-Assembly of the Gut-Derived Peptide Hormone PYY3-36.

Lipidation is a powerful strategy to improve the stability in vivo of peptide drugs. Attachment of a lipid chain to a hydrophilic peptide leads to amphiphilicity and the potential for surfactant-like self-assembly. Here, the self-assembly and conformation of three lipidated derivatives of the gastrointestinal peptide hormone PYY3-36 is examined using a comprehensive range of spectroscopic, scattering, and electron microscopy methods and compared to those of the parent PYY3-36 peptide. The peptides are lipidated at Ser(11), Arg(17), or Arg(23) in the peptide; the former is within the ß-turn domain (based on the published solution NMR structure), and the latter two are both within the α-helical domain. We show that it is possible to access a remarkable diversity of nanostructures ranging from micelles to nanotapes and fibrillar hydrogels by control of assembly conditions (concentration, pH, and temperature). All of the lipopeptides self-assemble above a critical aggregation concentration (cac), determined through pyrene fluorescence probe measurements, and they all have predominantly α-helical secondary structure at their native pH. The pH and temperature dependence of the α-helical conformation were probed via circular dichroism spectroscopy experiments. Lipidation was found to provide enhanced stability against changes in temperature and pH. The self-assembled structures were investigated using small-angle X-ray scattering (SAXS) and cryogenic transmission electron microscopy (cryo-TEM). Distinct differences in nanostructure were observed for lipidated and unlipidated peptides, also depending on the position of lipidation. Remarkably, micelles containing lipopeptides with α-helical peptide conformation were observed. Gelation was observed at higher concentrations in certain pH intervals for the lipidated peptides, but not for unlipidated PYY3-36. Thus, lipidation, in addition to enhancing stability against pH and temperature variation, also provides a route to prepare PYY peptide hydrogels. These findings provide important insights into the control of PYY3-36 conformation and aggregation by lipidation, relevant to the development of future therapeutics based on this peptide hormone, for example, in treatments for obesity.

The design and fabrication of supramolecular semiconductor nanowires formed by benzothienobenzothiophene (BTBT)-conjugated peptides.

π-Conjugated small molecules based on a [1]benzothieno[3,2-b]benzothiophene (BTBT) unit are of great research interest in the development of solution-processable semiconducting materials owing to their excellent charge-transport characteristics. However, the BTBT π-core has yet to be demonstrated in the form of electro-active one-dimensional (1D) nanowires that are self-assembled in aqueous media for potential use in bioelectronics and tissue engineering. Here we report the design, synthesis, and self-assembly of benzothienobenzothiophene (BTBT)-peptide conjugates, the BTBT-peptide (BTBT-C3-COHN-Ahx-VVAGKK-Am) and the C8-BTBT-peptide (C8-BTBT-C3-COHN-Ahx-VVAGKK-Am), as ß-sheet forming amphiphilic molecules, which self-assemble into highly uniform nanofibers in water with diameters of 11-13(±1) nm and micron-size lengths. Spectroscopic characterization studies demonstrate the J-type π-π interactions among the BTBT molecules within the hydrophobic core of the self-assembled nanofibers yielding an electrical conductivity as high as 6.0 × 10-6 S cm-1. The BTBT π-core is demonstrated, for the first time, in the formation of self-assembled peptide 1D nanostructures in aqueous media for potential use in tissue engineering, bioelectronics and (opto)electronics. The conductivity achieved here is one of the highest reported to date in a non-doped state.