title: 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.
authors.affiliation: Department of Physics and Astronomy, University of Texas at San Antonio, One UTSA Circle, San Antonio, TX, 78249, USA.
authors.forename: Rolando
authors.initials: R
authors.lastname: Valdez
authors.forename: Eric M
authors.initials: EM
authors.lastname: Johnson
authors.forename: John A
authors.initials: JA
authors.lastname: Belcher
authors.forename: John F
authors.initials: JF
authors.lastname: Fuini
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Brancaleon
mesh_terms: D000818:Animals; D002417:Cattle; D008854:Microscopy, Electron; D009391:Nephelometry and Turbidimetry; D011166:Porphyrins / Q000494:pharmacology*; D055503:Protein Multimerization / Q000187:drug effects*; D020836:Protein Structure, Quaternary / Q000187:drug effects; D012996:Solutions; D013050:Spectrometry, Fluorescence; D014404:Tubulin / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D011166:Porphyrins; D012996:Solutions; D014404:Tubulin