title: Effects of Visible-Light Irradiation of Protoporphyrin IX on the Self-Assembly of Tubulin Heterodimers.
abstract: 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.
authors.affiliation: Institut Quimic de Sarria, Universitat Ramon Llull, Via Augusta 390, 08017, Barcelona, Spain.|Department of Physics and Astronomy, University of Texas at San Antonio, San Antonio, TX, USA.
authors.forename: Alicia
authors.initials: A
authors.lastname: Vall-Sagarra
authors.affiliation: Department of Physics and Astronomy, University of Texas at San Antonio, San Antonio, TX, USA.
authors.forename: Brady
authors.initials: B
authors.lastname: McMicken
authors.affiliation: Institut Quimic de Sarria, Universitat Ramon Llull, Via Augusta 390, 08017, Barcelona, Spain.
authors.forename: Santi
authors.initials: S
authors.lastname: Nonell
authors.affiliation: Department of Physics and Astronomy, University of Texas at San Antonio, San Antonio, TX, USA. lorenzo.brancaleon@utsa.edu.
authors.forename: Lorenzo
authors.identifier: http://orcid.org/0000-0003-1039-339X
authors.initials: L
authors.lastname: Brancaleon
mesh_terms: D019281:Dimerization; D005453:Fluorescence; D008027:Light; D011524:Protoporphyrins / Q000737:chemistry*; D014404:Tubulin / Q000138:chemical synthesis / Q000737:chemistry*
chemical_list: D011524:Protoporphyrins; D014404:Tubulin; C028025:protoporphyrin IX
keywords: laser irradiation; microtubules; protein unfolding; protoporphyrin IX; tubulin