Intrinsic Fluorescence of Metabolite Amyloids Allows Label‐Free Monitoring of Their Formation and Dynamics in Live Cells

Abstract

The formation of apoptosis‐inducing amyloidal structures by metabolites has significantly extended the “amyloid hypothesis” to include non‐proteinaceous, single metabolite building blocks. However, detection of metabolite assemblies is restricted compared to their larger protein‐based counterparts owing to the hindrance of external labelling and limited immunohistochemical detection tools. Herein, we present the detection of the formation, dynamics, and cellular distribution of metabolite amyloid‐like structures and provide mechanistic insights into the generation of supramolecular chromophores. Moreover, the intrinsic fluorescence properties allow the detection of metabolite assemblies in living cells without the use of external dyes. Altogether, this intrinsic fluorescence of metabolite assemblies further verifies their amyloidal nature, while providing an important tool for further investigation of their pathological role in inborn error of metabolism disorders.

On-off transition and ultrafast decay of amino acid luminescence driven by modulation of supramolecular packing

“…The self-assembly of phenylalanine in aqueous solution was initiated by cooling a supersaturated solution of phenylalanine (40 mg/ml) at 90 °C to 20 °C, similar to previous work. 10 This leads to the formation of elongated fibrillary aggregates, as shown by bright-field microscopy (Figure 4a). The phenylalanine fibrils exhibited relative high fluorescence emission in the visible spectral range, which is absent in the monomeric state of phenylalanine, and characterized by the wavelength-dependent Stokes shift, i.e.…”

“…[7][8][9] It was shown that single amino acids in their aggregated form can also produce a fluorescent signal, which is not evident in the monomeric state. [10][11][12][13] Numerous observations suggest that the optical phenomenon of aggregation induced intrinsic fluorescence is broader than originally speculated, as it also applies to many other metabolites and nucleic acids. [14][15][16][17][18][19] Circumstantial evidence and argumentation suggested that supramolecular packing is important.…”

“…The phenomenon of aggregation-dependent luminescence of proteins is a rapidly evolving field. 1,2,17,[22][23][24][3][4][5][10][11][12][13]16 Protein aggregates were shown to absorb light at wavelengths above 300 nm and to exhibit a structure-specific fluorescence in the visible range, even in the absence of aromatic amino acids. 6 A plausible explanation for this phenomenon is the formation of structure-specific supramolecular fluorophores that are permissive to proton transfer across hydrogen bonds.…”

“…Indeed, we have shown that adenine, phenylalanine, tyrosine and tryptophan exhibit autofluorescence in the visible range upon self-assembly. 10 This allows the detection of metabolite assemblies within living cells, without any use of external dyes that could interfere with the ability to accurately model a given sample. 28 Other derivatives of tyrosine were also shown to exhibit luminescence upon aggregation.…”

Controlling the Self-Assembly of Biomolecules into Functional Nanomaterials through Internal Interactions and External Stimulations: A Review

“…In this review, we focus on the fabrication of biological nanomaterials by controlling the self-assembly of a biomolecule through internal biomolecular interactions and external stimulations. The main used/studied biomolecules, including proteins [ 7 , 41 ], peptides [ 42 , 43 ], amphiphiles [ 44 ], DNA [ 45 ], carbohydrates, metabolites [ 46 , 47 , 48 ], lipids, and cholesterol, for the self-assembly of various nanostructures are introduced and discussed in detail. In Section 2 , some recent studies are analyzed and discussed to illustrate the self-assembly mechanisms of various biomolecules, in which the strategies for creating biological nanomaterials via internal interactions are presented.…”