title: The binding mode of side chain- and C3-modified epothilones to tubulin.
abstract: The tubulin-binding mode of C3- and C15-modified analogues of epothilone A (Epo A) was determined by NMR spectroscopy and computational methods and compared with the existing structural models of tubulin-bound natural Epo A. Only minor differences were observed in the conformation of the macrocycle between Epo A and the C3-modified analogues investigated. In particular, 3-deoxy- (compound 2) and 3-deoxy-2,3-didehydro-Epo A (3) were found to adopt similar conformations in the tubulin-binding cleft as Epo A, thus indicating that the 3-OH group is not essential for epothilones to assume their bioactive conformation. None of the available models of the tubulin-epothilone complex is able to fully recapitulate the differences in tubulin-polymerizing activity and microtubule-binding affinity between C20-modified epothilones 6 (C20-propyl), 7 (C20-butyl), and 8 (C20-hydroxypropyl). Based on the results of transferred NOE experiments in the presence of tubulin, the isomeric C15 quinoline-based Epo B analogues 4 and 5 show very similar orientations of the side chain, irrespective of the position of the nitrogen atom in the quinoline ring. The quinoline side chain stacks on the imidazole moiety of beta-His227 with equal efficiency in both cases, thus suggesting that the aromatic side chain moiety in epothilones contributes to tubulin binding through strong van der Waals interactions with the protein rather than hydrogen bonding involving the heteroaromatic nitrogen atom. These conclusions are in line with existing tubulin polymerization and microtubule-binding data for 4, 5, and Epo B.
authors.affiliation: NMR-Based Structural Biology, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany.
authors.forename: Máté
authors.initials: M
authors.lastname: Erdélyi
authors.forename: Armando
authors.initials: A
authors.lastname: Navarro-Vázquez
authors.forename: Bernhard
authors.initials: B
authors.lastname: Pfeiffer
authors.forename: Christian N
authors.initials: CN
authors.lastname: Kuzniewski
authors.forename: Andrea
authors.initials: A
authors.lastname: Felser
authors.forename: Toni
authors.initials: T
authors.lastname: Widmer
authors.forename: Jürg
authors.initials: J
authors.lastname: Gertsch
authors.forename: Benet
authors.initials: B
authors.lastname: Pera
authors.forename: José Fernando
authors.initials: JF
authors.lastname: Díaz
authors.forename: Karl-Heinz
authors.initials: KH
authors.lastname: Altmann
authors.forename: Teresa
authors.initials: T
authors.lastname: Carlomagno
mesh_terms: D000818:Animals; D001665:Binding Sites; D002417:Cattle; D045744:Cell Line, Tumor; D003198:Computer Simulation; D034261:Epothilones / Q000737:chemistry* / Q000494:pharmacology; D006801:Humans; D009682:Magnetic Resonance Spectroscopy; D017434:Protein Structure, Tertiary; D013329:Structure-Activity Relationship; D014404:Tubulin / Q000737:chemistry* / Q000378:metabolism; D050257:Tubulin Modulators / Q000737:chemistry* / Q000494:pharmacology
chemical_list: D034261:Epothilones; D014404:Tubulin; D050257:Tubulin Modulators