  In this study, we employed a Raman spectroscopic analysis of the amide I band
of polymerized samples of tubulin exposed to pulsed low-intensity NIR radiation
(810 nm, 10 Hz, 22.5 J/cm$^{2}$ dose). Peaks in the Raman fingerprint region
(300$\unicode{x2013}$1900 cm$^{-1}$), in particular, in the amide I band
(1600$\unicode{x2013}$1700 cm$^{-1}$), can be used to quantify the percentage
of protein secondary structures. Under this band, hidden signals of
$\mathrm{C}$=$\mathrm{O}$ stretching, belonging to different structures, are
superimposed$\unicode{x2014}$producing a complex signal as a result. An
accurate decomposition of the amide I band is therefore required for the
reliable analysis of the conformation of proteins, which we achieved through a
straightforward method employing a Voigt profile. This approach was validated
through secondary structure analyses of unexposed control samples, for which
comparisons with other values available in the literature could be conducted.
Subsequently, using this validated method, we present novel findings of
statistically significant alterations in the secondary structures of
NIR-exposed tubulin, characterized by a notable decrease in alpha-helix content
and a concurrent increase in beta-sheets compared to the control samples. The
alpha-helix to beta-sheet transition suggests that PBM reduces microtubule
stability and introduces dynamism to allow for the remodeling and,
consequently, refreshing of microtubule structures. This newly discovered
mechanism could have implications for reducing the risks associated with brain
aging, including neurodegenerative diseases like Alzheimer's disease.
