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Effects of Visible‐Light Irradiation of Protoporphyrin IX on the Self‐Assembly of Tubulin Heterodimers
Author(s) -
VallSagarra Alicia,
McMicken Brady,
ll Santi,
Brancaleon Lorenzo
Publication year - 2016
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.201600629
Subject(s) - protoporphyrin ix , chemistry , tubulin , irradiation , photochemistry , singlet oxygen , microtubule , biophysics , monomer , tryptophan , fluorescence , kinetics , photodynamic therapy , oxygen , biochemistry , organic chemistry , biology , physics , nuclear physics , microbiology and biotechnology , amino acid , quantum mechanics , polymer
The formation and the effects of laser irradiation of the complex formed by protoporphyrin IX (PPIX) and tubulin was investigated. We have used tubulin as a model protein to investigate whether docked photoactive ligands can affect the structure and function of polypeptides upon exposure to visible light. We observed that laser irradiation in the Soret band prompts bleaching of the PPIX, which is accompanied by a sharp decrease in the intensity and average fluorescence lifetime of the protein (dominated by the four tryptophan residues of the tubulin monomer). The kinetics indicate non‐trivial effects and suggest that the photosensitization of the PPIX bound to tubulin prompts structural alterations of the protein. These modifications were also observed through changes in the energy transfer between Trp residues and PPIX. The results suggest that laser irradiation produces localized partial unfolding of tubulin and that the changes prompt modification of the formation of microtubules in vitro. Measurements of singlet oxygen formation were inconclusive in determining whether the changes are prompted by reactive oxygen species or other excited state mechanisms.