Investigating Intrinsic Fluorescence Mechanisms in Amyloid Fibers

Fluorescent tags are minimally invasive fluorophore markers that can be used to identify proteins and monitor protein interactions for imaging and structural analysis. One advantage of fluorescent tagging is that they are largely non-toxic, which means they can be used in live cells. For example, the artificial fluorescent tag Thioflavin T (ThT) is used for identifying amyloid fibers, protein aggregates that are often associated with diseases such as Parkinson’s, Alzheimer’s, and Type II Diabetes. Recently we have found that amyloid fibers have an intrinsic fluorescence that can be used instead of an artificial dye like ThT. Here, we investigate this excitation-dependent fluorescence signal in fibers formed from Hen Egg White Lysozyme (HEWL). Batches of amyloid fibers were grown from HEWL, with each batch varying in external conditions. We find that these lysozyme amyloid fibers have a previously unidenfied absorbance peak at 350 nm separate from the UV signal given off by tryptophan at 280 nm. We also observe the excitation-dependent fluorescence from in the range of 420-500 nm with a Stokes shift of ~90 nm. By changing the growing conditions of the fibers, we have uncovered a potential correlation between fiber morphology and peak wavelength. We correlate these changes in intrinsic fluorescence to adjustments in amyloid structure caused by the change in external growing conditions. By better understanding the correlation between fiber structure and their fluorescence pattern, fluorescence can be used to identify proteins without the addition of dyes.