title: Photoinduced partial unfolding of tubulin bound to meso-tetrakis(sulfonatophenyl) porphyrin leads to inhibition of microtubule formation in vitro.
abstract: The irradiation of the complex formed by meso-tetrakis (sulfonatophenyl) porphyrin (TSPP) and tubulin was investigated as well as its effects on the structure and function of the protein. We have used tubulin as a model target to investigate whether photoactive ligands docked to the protein can affect the structure and function of the protein upon exposure to visible light. We observed that laser irradiation prompts bleaching of the porphyrin which is accompanied by a sharp decrease (∼2 ns) in the average fluorescence lifetime of the protein and a change in the dichroic spectrum consistent with a decrease of helical structure. The result indicated the photoinduced partial unfolding of tubulin. We also observed that such partial conformational change inhibits the formation of microtubules in vitro. We investigated whether photosensitization of reactive oxygen species was responsible for these effects. Even upon removal of O2 the protein still undergoes conformational changes indicating that irradiation of the bound porphyrin does not require the presence of O2 to prompt conformational and functional effects opening the possibility that other mechanisms (e.g., charge transfer) are responsible for the photoinduced mechanism.
authors.affiliation: The University of Texas at San Antonio, Department of Physics and Astronomy, One UTSA Circle, San Antonio, Texas, 78249 USA; Optical Radiation Bioeffects Branch, Bioeffects Division, Air Force Research Laboratory, Fort Sam Houston, Texas 78234, USA.
authors.forename: Brady
authors.initials: B
authors.lastname: McMicken
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Thomas
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Brancaleon
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism; D002942:Circular Dichroism; D008024:Ligands; D018625:Microscopy, Atomic Force; D008870:Microtubules / Q000378:metabolism*; D010100:Oxygen / Q000737:chemistry; D010777:Photochemistry / Q000379:methods; D011166:Porphyrins / Q000737:chemistry*; D011487:Protein Conformation; D011489:Protein Denaturation; D017510:Protein Folding; D017382:Reactive Oxygen Species; D013050:Spectrometry, Fluorescence / Q000379:methods; D013059:Spectrum Analysis, Raman; D013552:Swine; D014404:Tubulin / Q000737:chemistry*
chemical_list: D008024:Ligands; D011166:Porphyrins; D017382:Reactive Oxygen Species; D014404:Tubulin; C016136:tetraphenylporphine sulfonate; D010100:Oxygen
keywords: atomic force microscopy; circular dichroism; porphyrin; protein unfolding; tubulin