Identification of seco-clavilactone B as a small-molecule actin polymerization inhibitor.

Phenotype-based chemical screening is an attractive strategy for the identification of bioactive compounds. We searched for a compound that induces cellular morphological change and identified a novel compound that we named seco-clavilactone B (Seco-CB). Treatment with Seco-CB decreased the ratio of filament actin (F-actin) to globular actin (G-actin). An in vitro actin polymerization assay revealed that Seco-CB inhibited actin polymerization directly. Further analysis demonstrated that the inhibitory effect of Seco-CB on actin polymerization was associated with Seco-CB binding to either Thr5 or Cys285 of actin. These data indicate that Seco-CB is a novel actin polymerization inhibitor.