A Structural Basis for Regulation of Actin Polymerization by Pectenotoxins

Abstract

(PTXs) are polyether macrolides found in certain dinoflagellates, sponges and shellfish, and have been associated with diarrhetic shellfish poisoning. In addition to their in vivo toxicity, some PTXs are potently cytotoxic in human cancer cell lines. Recent studies have demonstrated that disruption of the actin cytoskeleton may be a key function of these compounds, although no clarification of their mechanism of action at a molecular level was available. We have obtained an X-ray crystal structure of PTX-2 bound to actin, which, in combination with analyses of the effect of PTX-2 on purified actin filament dynamics, provides a molecular explanation for its effects on actin. PTX-2 formed a 1:1 complex with actin and engaged a novel site between subdomains 1 and 3. Based on models of the actin filament, PTX binding would disrupt key lateral contacts between the PTX-bound actin monomer and the lower lateral actin monomer within the filament, thereby capping the barbed-end. The location of this binding position within the interior of the filament indicates that it may not be accessible once polymerization has occurred, a hypothesis supported by our observation that PTX-2 caused filament capping without inducing filament severing. This mode of action is unique, as other actin filament destabilizing toxins appear to exclusively disrupt longitudinal monomer contacts, allowing many of them to sever filaments in addition to capping them. Examination of the PTX-binding site on actin provides a rationalization for the structure-activity relationships observed in vivo and in vitro, and may provide a basis for predicting toxicity of PTX analogues.

Truncated Latrunculins as Actin Inhibitors Targeting Plasmodium falciparum Motility and Host Cell Invasion

“…As can be seen from Table 2, the latrunculin core analogues follow the same trend in activity with the T. gondii as they did with the P. falciparum. The ester analogues with alkyl chain (10) and cyclopentane ring (11) were inactive while the benzoate ester analogues with ortho substitutions (15)(16)(17) were active. The fact that the activity in the P. falciparum is mimicked by the T. gondii parasites supports the notion that these truncated latrunculin analogues likely target the apicomplexan actin as their binding site.…”

Synthetic Studies towards Pectenotoxin‐2: Synthesis of the Nonanomeric 10‐epi‐ABCDE Ring Segment by Kinetic Spiroketalization

“…[20] Entry Acid Solvent The stereochemistry at C10, however, could not be fully confirmed by NOE experiments. We therefore decided to convert the [6,5]-spiroketal system of the product into the corresponding [6,6]-spiroketal system. This was readily achieved by deprotection of the silyl protecting groups with tetrabutylammonium fluoride (TBAF), followed by treatment with p-toluenesulfonic acid (pTsOH) to afford the desired [6,6]-spiroketal 31a (Scheme 7).…”

“…[6] Synthetic access to the pectenotoxins bearing the full natural configura-tion, including the nonanomeric R configuration at the C7 spiro carbon, is therefore an important, but challenging, objective in marine natural product synthesis. [7,8] Herein, we outline our progress towards the synthesis of the nonanomeric ABCDE ring segment of PTX2.…”

Pectenotoxin-2 induces G1 arrest of the cell cycle in synovial fibroblasts of patients with rheumatoid arthritis

“…(8). Previous in vitro and in vivo studies have shown that PTX-2, through its binding site with actin, can modify the actin cytoskeleton by promoting actin depolymerization (9,10). In addition, this compound also displays selective and potent cytotoxicity against human cancer cells (11,12), as well as inducing Bim/Bax-mediated apoptosis in p53-deficient tumors (13).…”