Latrunculin A is used extensively as an agent to sequester monomeric actin in living cells. We hypothesize that additional activities of latrunculin A may be important for its biological activity. Our data are consistent with the formation of a 1:1 stoichiometric complex with an equilibrium dissociation constant of 0.2 to 0.4 μm and provide no evidence that the actin-latrunculin A complex participates in the elongation of actin filaments. Profilin and latrunculin A bind independently to actin, whereas binding of thymosin β4 to actin is inhibited by latrunculin A. Potential implications of this differential effect on actin-binding proteins are discussed. From a structural perspective, if latrunculin A binds to actin at a site that sterically influences binding by thymosin β4, then the observation that latrunculin A inhibits nucleotide exchange on actin implies an allosteric effect on the nucleotide binding cleft. Alternatively, if, as previously postulated, latrunculin A binds in the nucleotide cleft of actin, then its ability to inhibit binding by thymosin β4 is a surprising result that suggests that significant allosteric changes affect the thymosin β4 binding site. We show that latrunculin A and actin form a crystalline structure with orthorhombic space group P212121and diffraction to 3.10 Å. A high resolution structure with optimized crystallization conditions should provide insight regarding these remarkable allosteric properties.
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Published, JBC Papers in Press, June 19, 2000, DOI 10.1074/jbc.M004253200
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