## 3 Amyloid-like Assemblies Exhibiting Intrinsic Visible Fluorescence
### Peptides
#### 3.2.1 Linear Peptides  
The ability of self-assembled peptides to generate visible fluorescence was reported nearly 20 years ago when [PERSON] et al. [37] described this peculiar spectroscopic property for the peptide with sequence NDSIRSCRLIPQHT, which does not present any aromatic fluorescent residue in its sequence. The ability to emit fluorescence in the visible region by self-assembled systems made of peptide chains composed of non-aromatic residues was confirmed by the characterization of fibrils formed by poly(VGGLG) [71]. Structural and spectroscopic investigations on self-assembled peptides have been significantly stimulated via the discovery that the dissection of aggregating proteins could generate peptide fragments forming different supramolecular assemblies, including amyloids. As reported \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Protein System**} & \multirow{2}{*}{**UniProt ID**} & \multicolumn{2}{c}{**Excitation, Emission Wavelength/Range (hexx, Lem)**} & \multirow{2}{*}{**Methodology Used for the Experiment**} & \multirow{2}{*}{**Physical State of the Sample**} & \multirow{2}{*}{**Ref.**} \\ \cline{3-4} \cline{6-7}  & & **UV-Blue** & & & & \\ \hline \multirow{9}{*}{\begin{tabular}{c} Human \\ transthyretin (TTR) \\ \end{tabular} } & \multirow{3}{*}{P02766} & 360 nm, & Fluorescence & Protein & [64] \\  & & 417/438/480 nm & & spectroscopy & solution & [65] \\ \cline{1-1} \cline{3-4}  & & 360 nm, & & Fluorescence & Protein & [65] \\ \cline{1-1} \cline{3-4}  & & 400/420 nm, & & Fluorescence & [66] \\ \cline{1-1} \cline{3-4}  & & 360 nm, & & spectroscopy & solution & [66] \\ \cline{1-1} \cline{3-4}  & & 417/438 nm & & & & \\ \hline Double Plant & \multirow{3}{*}{Q92784} & \multirow{3}{*}{350 nm, 460 * nm (DPF3a)} & \multirow{3}{*}{\
\begin{tabular}{c} Fluorescence \\ spectroscopy \\ \end{tabular} } & \multirow{3}{*}{
\begin{tabular}{c} Amyloid fiber \\ suspension \\ \end{tabular} } & \multirow{3}{*}{[66]} \\  & & & & Fluorescence & Amyloid fiber \\ \cline{1-1} \cline{3-4}  & & & & spectroscopy & suspension & [66] \\ \cline{1-1} \cline{3-4}  & & & & & \\ \hline DPF3a (residues 200-357) and & \multirow{3}{*}{Q92784} & \multirow{3}{*}{400 nm, 460 nm} & Fluorescence & Amyloid fiber & [67] \\ \cline{1-1} \cline{3-4}  & & & & Fluorescence & [68] \\ \cline{1-1} \cline{3-4}  & & & & spectroscopy & suspension & [68] \\ \cline{1-1} \cline{3-4}  & & & & & \\ \hline Class I & \multirow{3}{*}{Q8 WZI2} & \multirow{3}{*}{345 nm, 450 nm} & Fluorescence & Protein & [69] \\ \cline{1-1} \cline{3-4}  & & & & spectroscopy & solution & [69] \\ \cline{1-1} \cline{3-4}  & & & & & \\ \cline{1-1} \cline{3-4}  & & & & & \\ \cline{1-1} \cline{3-4}  & & & & & \\ \hline TasA & \multirow{3}{*}{P54507} & \multirow{3}{*}{350 nm, 435 nm} & Fluorescence & Amyloid fiber & [48] \\ \cline{1-1} \cline{3-4}  & & & & spectroscopy & [48] \\ \cline{1-1} \cline{3-4}  & & & & spectroscopy & [48] \\ \cline{1-1} \cline{3-4}  & & & & & \\ \hline GRASP ancestors & \multirow{3}{*}{N.R.**} & \multirow{3}{*}{365 nm, 450 * nm (for ANC4)} & 365 nm, 510 * (for ANC4) & Fluorescence & Protein & [70] \\ \cline{1-1} \cline{3-4}  & & & & & \\ \cline{1-1} \cline{3-4}  & & & & & \\ \cline{1-1} \cline{3-4}  & & & & & \\ \cline{1-1} \cline{3-4}  & & & & & \\ \hline \hline \end{tabular}  
* Data inferred from the figures of the related reference. ** Not reported (N.R.).  
\end{table} 
Table 1: \(Cont.\)in Table 2, fluorescent peptide aggregates were derived from several proteins, including \(\gamma\)-crystallin, human serum albumin, nucleophosmin, \(\beta\)-lactoglobulin, transthyretin, elastin, and the homeobox protein PKNOX1 (also denoted as PREP1). Similarly, self-assembling fluorescent peptides were also obtained via the fragmentation of polypeptides such as A\(\beta\)(1-42) or islet amyloid polypeptide human amylin (hIAPP). These peptides present a large spectrum of variability in terms of size, amino acid composition, and polarity. Interestingly, fluorescent amyloids are also formed by linear dipeptides.