Spatiotemporal Control of Melanin Synthesis in Liquid Droplets

Abstract

Melanins are natural biopolymers that have remarkable properties including UV-protection, coloration, and antioxidant activity. Their biosynthesis is regulated both spatially and temporally and involves supramolecular templating and compartmentalization of enzymes and reactants within specialized organelles called melanosomes. In contrast, the laboratory-based bulk synthesis of melanin by tyrosine or dopamine oxidation is a poorly controlled process, resulting in materials with undefined properties. Inspired by the pigment’s biosynthesis, we developed a methodology to spatiotemporally regulate melanin formation in liquid droplets. The spatial control is achieved by sequestration of the reaction in dextran-rich droplets of a polyethylene glycol/dextran aqueous two-phase system, where the use of a photocleavable protected tyrosine provides a temporal control over its enzymatic oxidation–polymerization. We show that the liquid droplets allow for confined local reactivity as they serve as reaction centers for melanin synthesis and compartmentalize the melanin product. This methodology opens tremendous opportunities for applications in skincare and biomedicine.

Localized and regulated peptide pigment formation inside liquid droplets through confined enzymatic oxidation

“…In addition, droplets containing oxidized tyrosine showed intrinsic fluorescent emission upon excitation at l = 405 nm. 21 As expected, fluorescence intensity of oxidized DYFR 9 was significantly higher compared to its surroundings (Fig. S2, ESI †).…”

“…Lampel's group demonstrated the use of polyethylene glycol/dextran aqueous two-phase system with a photocleavable protected tyrosine, which gave rise to oxidized tyrosine induced in a LLPS system. 21 In this system, the condensates served as a reaction vessel in which tyrosine can be oxidized. 21 Using short peptides have also been recognized to form short peptides.…”

“…21 In this system, the condensates served as a reaction vessel in which tyrosine can be oxidized. 21 Using short peptides have also been recognized to form short peptides. 22 Here, it was our objective to control the generation of melanin mimics in a LLPS system where the tyrosine residues are themselves a structural part of the condensates.…”

“…Our findings align with previously established literature that has measured tyrosine oxidation products using UV-vis, 6,7,27,28 and tyrosine oxidation within coacervates. 21 Matrix Assisted Laser Desorption/Ionization (MALDI) was used to analyze and confirm tyrosine oxidation. Tyrosinecontaining peptides undergo polymerization in which change in molecular weight is observed after oxidation, which can be visualized through MALDI.…”

Microfluidic Aqueous Two-Phase Focusing of Chemical Species for In Situ Subcellular Stimulation

“…The phase interface is a promising tool to confine chemical species. Among all the interfaces, the interface of aqueous two-phase systems (ATPS) has a unique superiority: phases on both sides of the interface show good biocompatibility, – enabling various cellular applications. – Biomolecules usually have preference over one phase of ATPS, ,, and the partition properties can be extensively adjusted, – bringing wide applications in extraction, separation, and microreactors. ,, Low interfacial tensions is a disadvantage for conventional ATPS droplet applications, ,, but it makes the two phases favor stable laminar flow, facilitating the manipulation by a microfluidic probe. However, even though the chemical species has a preference for one phase, it will still diffuse to the other phase until the partition ratio is reached .…”