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Porphyrins affect the self-assembly of tubulin in solution.

ABSTRACT: Self-assembly of tubulin heterodimers in solution has been studied in the past to predict the effects that ligands and/or conformational changes have on the formation of tubulin filaments. Self-assembly of tubulin in solution has produced formations similar to cellular microtubules (MTs). The present study reports on the effects that two porphyrins (protoporphyrin IX, PPIX and tetrakis(4-sulfonatophenyl)porphyrin, TPPS) produce on the self-assembly of tubulin alpha,beta-heterodimers in buffer solution. The study shows that, when incubated simultaneously with MT-stabilizing ligands (i.e., paclitaxel and guanosine triphosphate, GTP), porphyrins do not affect the ability of tubulin to form MT. However, if paclitaxel and GTP are added after tubulin has been allowed to self-assemble in the presence of either porphyrin, the ability to form MT-like structures is reduced or suppressed. We suggest that this effect is due to the formation of porphyrin-mediated aggregates that cannot be broken or elongated by the addition of GTP or paclitaxel.

SUBMITTER: Valdez R

PROVIDER: S-EPMC2783650 | biostudies-literature | 2009 Dec

REPOSITORIES: biostudies-literature

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Porphyrins affect the self-assembly of tubulin in solution.

Valdez Rolando R Johnson Eric M EM Belcher John A JA Fuini John F JF Brancaleon Lorenzo L

Biophysical chemistry 20090929 2-3

Self-assembly of tubulin heterodimers in solution has been studied in the past to predict the effects that ligands and/or conformational changes have on the formation of tubulin filaments. Self-assembly of tubulin in solution has produced formations similar to cellular microtubules (MTs). The present study reports on the effects that two porphyrins (protoporphyrin IX, PPIX and tetrakis(4-sulfonatophenyl)porphyrin, TPPS) produce on the self-assembly of tubulin alpha,beta-heterodimers in buffer so ...[more]

PMID: 19819610

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Project description:The study of excited-state energy diffusion has had an important impact in the development and optimization of organic electronics. For instance, optimizing excited-state energy migration in the photoactive layer in an organic solar cell device has been shown to yield efficient solar energy conversion. Despite the crucial role that energy migration plays in molecular electronic device physics, there is still a great deal to be explored to establish how molecular orientation impacts energy diffusion mechanisms. In this work, we have synthesized a new library of solution-processable, Zn (alkoxycarbonyl)phenylporphyrins containing butyl (ZnTCB4PP), hexyl (ZnTCH4PP), 2-ethylhexyl (ZnTCEH4PP), and octyl (ZnTCO4PP) alkoxycarbonyl groups. We establish that, by varying the length of the peripheral alkyl chains on the metalloporphyrin macrocycle, preferential orientation and molecular self-assembly is observed in solution-processed thin films. The resultant arrangement of molecules consequently affects the electronic and photophysical characteristics of the metalloporphyrin thin films. The various molecular arrangements in the porphyrin thin films and their resultant impact were determined using UV-Vis absorption spectroscopy, steady-state and time-resolved fluorescence emission lifetimes, and X-ray diffraction in thin films. The films were doped with C60 quencher molecules and the change in fluorescence was measured to derive a relative quenching efficiency. Using emission decay, relative quenching efficiency, and dopant volume fraction as input, insights on exciton diffusion coefficient and exciton diffusion lengths were obtained from a Monte Carlo simulation. The octyl derivative (ZnTCO4PP) showed the strongest relative fluorescence quenching and, therefore, the highest exciton diffusion coefficient (5.29 × 10-3 cm2 s-1) and longest exciton diffusion length (~81 nm). The octyl derivative also showed the strongest out-of-plane stacking among the metalloporphyrins studied. This work demonstrates how molecular self-assembly can be used to modulate and direct exciton diffusion in solution-processable metalloporphyrin thin films engineered for optoelectronic and photonic applications.

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Porphyrins affect the self-assembly of tubulin in solution.

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Porphyrins affect the self-assembly of tubulin in solution.

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