Partial Unfolding of Tubulin Heterodimers Induced by Two-Photon Excitation of Bound meso-Tetrakis(sulfonatophenyl)porphyrin

Abstract

The water-soluble porphyrin meso-tetrakis(p-sulfonatophenyl)porphyrin (TSPP) can be noncovalently bound to tubulin and used as a photosensitizer, which upon irradiation triggers photochemical reactions that lead to conformational changes of the protein. These conformational changes in turn inhibit tubulin's primary function of polymerizing into microtubules. We explored the possibility of using two-photon excitation of the bound porphyrin to induce photosensitized protein unfolding. Although TSPP has a relatively low cross section (∼30 GM) our results did find that two-photon excitation of the ligand causes partial unfolding of the tubulin host and the inhibition of the in vitro formation of microtubules. Conversely, irradiating tubulin alone caused no such effects despite the large irradiance per pulse (97-190 GW/cm(2)). The conformational changes were characterized using spectroscopic studies and provide a promising protocol for the future application of non-native photosensitization of proteins.

Effects of Visible‐Light Irradiation of Protoporphyrin IX on the Self‐Assembly of Tubulin Heterodimers

“…The combination of experimental and computational results suggest that this site is a likely docking site for PPIX. In addition, this location is not distant from the one we recently established for a water soluble porphyrin [31] and does confirm that PPIX is unlikely to disrupt the formation of MTs.…”

Unveiling the Potential of Unfused Bichromophoric Naphthalimide To Induce Cytotoxicity by Binding to Tubulin: Breaks Monotony of Naphthalimides as Conventional Intercalators

“…So, the compounds that can suppress spindle MT dynamics and intervene with cell division process or metaphase to anaphase transition point may serve as potentially fruitful avenue for future antimitotic drug development. Several structurally diverse compounds − that may bind to any one of the three well-known characterized tubulin binding sites (colchicine site and vinblastine sites as well as taxol site) either destabilize or stabilize MTs by perturbing the mitotic spindle functions and inhibiting cell division at the interphase or metaphase to anaphase transition of mitosis. The first of these groups which destabilize the MTs include vinca alkaloids, cryptophycins, colchicine, and vinblastine that have distinct binding sites on tubulin, − whereas the second group of compounds which stabilize the MTs include epothilones, taxol, and discodermolide that share overlapping binding sites in tubulin. , The clinical success of vinca alkaloids, estamustine, and taxanes has prompted the search for new anticancer agents that target MTs, and several MT poisons are currently undergoing clinical trials for cancer chemotherapy. ,, …”