Misakinolide A is a marine macrolide that caps but does not sever filamentous actin.
We have investigated the biochemical properties of the marine natural product, misakinolide A, a 40-membered dimeric lactone macrolide that differs from swinholide A only in the size of the macrolide ring. Analytical ultracentrifugation and steady-state fluorescence experiments show that misakinolide A binds simultaneously to two actin subunits with virtually the same affinity as swinholide A, suggesting that the modification in the ring size does not change the actin-binding site. Sedimentation equilibrium experiments suggest that binding is independent at each binding site, with a Kd of approximately 50 nM. Remarkably, misakinolide A does not sever actin filaments like swinholide A; rather, it caps the barbed end of F-actin. When capped by misakinolide A, the elongation rate constant at the barbed end is reduced to zero; pointed end growth was affected only to the extent that the compound sequesters unpolymerized actin. Misakinolide A has essentially no effect on the off-rate of actin subunits leaving the barbed end. Energy-minimized models of misakinolide A and swinholide A are consistent with conservation of identical binding sites in both molecules, but a difference in orientation of one binding site relative to the other may explain why swinholide A has severing activity whereas misakinolide A only has capping activity.
Terry
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Department of Medicine, Health Science Center, University of Florida College of Medicine, Gainesville, Florida 32610, USA.
Spector
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Higa
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Bubb
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D000199:Actins / Q000737:chemistry*; D001704:Biopolymers; D018942:Macrolides / Q000737:chemistry*; D015394:Molecular Structure; D013050:Spectrometry, Fluorescence
D000199:Actins; D001704:Biopolymers; D018942:Macrolides; C104924:bistheonellide A