Peloruside A

Preserving the integrity of neuronal microtubules (MTs) has emerged as a promising strategy to inhibit the progression of neurodegenerative disorders such as Alzheimer's disease. Such a goal could be achieved by peptides that mimic the functional role of Tau, an MT-associated protein that stabilizes MTs by dynamically binding to their outer surface. This work examines the binding properties and MT-stabilizing potential of a 27-amino acid Tau oligopeptide from 300 ns Gaussian-accelerated molecular dynamics simulations and Molecular Mechanics/Generalized Born Surface Area (MM/GBSA) calculations on octameric MT models bound to two equivalent and independent Tau peptides. Bound peptides adopted extended conformations that are highly consistent with cryo-electron microscopy reports for full-length Tau bound to MTs. Anchoring points in three consecutive tubulin subunits were identified, with a relevant contribution of the Ser419-Val435 region to α-tubulin. Tau peptides strengthen the longitudinal protein-protein contacts within the MT lattice and exert a cooperative MT-stabilizing effect in MT complexes simultaneously bonded to taxol or peloruside A. Ser phosphorylation results in a larger peptide mobility, altered interaction profiles, and MT destabilization, which are in line with the loss of MT integrity resulting from the post-translational hyperphosphorylation of Tau. Our results shed light on the MT-stabilizing potential of Tau-mimetic peptides to act as novel neuroprotective agents targeting MTs.

Microtubules (MTs) play an essential role in mitosis; hence they are identified as potential targets to design novel anti-mitotic agents. MT's are composed of α/β-tubulin isotypes that are associated with differential drug-resistant effects against MT-targeting agents. Peloruside-A (PLA) is a potent anti-mitotic agent showing excellent activity against taxol-resistant carcinoma. PLA alters MT dynamics by binding to the 'non-taxoid' site of β-tubulin. The abundance of βII and βIII tubulin isotypes in human ovarian carcinoma affects the efficacy of PLA. Nevertheless, the mechanism of PLA resistance due to βII and βIII tubulin isotype is not well understood. Therefore, we investigated the interactions of PLA with αβIIa, αβIIb, and αβIII tubulin isotypes which are predominantly expressed in the human ovarian carcinoma, using a molecular modeling approach. A sequence analysis study shows that the βIII isotype has seven residue variations at the 'non-taxoid' site compared to the βIIa and βIIb isotypes. Molecular docking and molecular dynamics simulation revealed that residue variation at the 'non-taxoid' site of βIII isotype affect PLA binding. Furthermore, binding energy calculations showed that αβIIa has the highest binding towards PLA, whereas αβIIb and αβIII isotypes shows weaker associations with PLA. Our computational study provides valuable structural and energetic information to increase understanding into the origin of PLA resistance in human ovarian carcinoma and could be helpful to develop potential PLA analogs against specific β-tubulin isotypes expressed in cancer cells.Communicated by Ramaswamy H. Sarma.