Direct Evidence of Intrinsic Blue Fluorescence from Oligomeric Interfaces of Human Serum Albumin

Abstract

The molecular origin behind the concentration-dependent intrinsic blue fluorescence of human serum albumin (HSA) is not known yet. This unusual blue fluorescence is believed to be a characteristic feature of amyloid-like fibrils of protein/peptide and originates due to the delocalization of peptide bond electrons through the extended hydrogen bond networks of cross-β-sheet structure. Herein, by combining the results of spectroscopy, size exclusion chromatography, native gel electrophoresis, and confocal microscopy, we have shown that the intrinsic blue fluorescence of HSA exclusively originates from oligomeric interfaces devoid of any amyloid-like fibrillar structure. Our study suggests that this low energy fluorescence band is not due to any particular residue/sequence, but rather it is a common feature of self-assembled peptide bonds. The present findings of intrinsic blue fluorescence from oligomeric interfaces pave the way for future applications of this unique visual phenomenon for early stage detection of various protein aggregation related human diseases.

The acute myeloid leukemia‐associated Nucleophosmin 1 gene mutations dictate amyloidogenicity of the C‐terminal domain

“…Furthermore the same sequences showed an intrinsic fluorescence that is often associated to amyloid‐like fibrillar structure of proteins and peptides , moreover the emission spectra resulted dependent on the excitation wavelength, as shown in Fig. .…”

“…Similarly, b-aggregates of mutC short gave a constant signal in the time interval 16-100 h, while the reduction and the blue-shift of k max for mutF short in the interval 24-40 h suggests the onset of insoluble fibrils. Furthermore the same sequences showed an intrinsic fluorescence that is often associated to amyloid-like fibrillar structure of proteins and peptides [32], moreover the emission spectra resulted dependent on the excitation wavelength, as shown in Fig. 5.…”

Enhanced Luminescent Properties of Photo‐Stable Copper Nanoclusters through Formation of “Protein‐Corona”‐Like Assemblies

“…However, from the graph (Figure a), it is clearly evident that the effective increment in luminescence intensity at higher concentration of HSA is marginally low. This can be attributed the possible existence of some free HSA molecules which have a minimal blue luminescence when excited at 340 nm …”

Spectroscopic Analysis of Protein‐Crowded Environments Using the Charge‐Transfer Fluorescence Probe 8‐Anilino‐1‐Naphthalenesulfonic Acid

“…Of note is that the fluorescence spectra in the blue edge region (420 nm) are slightly starting to increase at 10 mg/ml (Figure (b)). This subtle change can be assigned to the oligomerization of BSA as described in Suppurating information 2 (Figure S2) . In this manner, although the apparent ANS fluorescence intensity changes as the BSA concentration increases, the ANS spectral shape and position do not change, which could indicate that the crowded environment does not hardly affect the microenvironment in hydrophobic pockets of BSA.…”

“…Therefore, the fluorescence intensity may decrease apparently with the increase of concentration. Another reason could be that the newly originated absorption band around 350 nm due to the formation of oligomer in the highly concentrated region could absorb the excitation light, [51] thus, the excitation intensity for ANS molecules relatively decreases, as is discussed in Supporting information 2. Figure 7(c) shows the normalized fluorescences of ANS in BSA solutions at 0.01, 0.1, 1, 10, 100 and 300 mg/ml and in BSA/ trehalose glass.…”