Actin-depolymerizing effect of dimeric macrolides, bistheonellide A and swinholide A.
We compared the effects of dimeric marine toxins, bistheonellide A, and swinholide A, on actin polymerization. Bistheonellide A and swinholide A possess two identical side chains with similar structures to those of other marine toxins, mycalolide B, and aplyronine A. By monitoring changes in fluorescent intensity of pyrenyl-actin, bistheonellide A was found to inhibit polymerization of G-actin and to depolymerize F-actin in a concentration-dependent manner. The relationship between the concentration of bistheonellide A and its inhibitory activity on actin polymerization suggested that one molecule of bistheonellide A binds two molecules of G-actin. We demonstrated by SDS-PAGE that the complex of G-actin with bistheonellide A, swinholide A, or mycalolide B could not interact with myosin. No evidence was found that bistheonellide A severs F-actin at the concentrations examined (molar ratio to actin; 0. 025-2.5), while swinholide A showed severing activity, although it was weaker than that of mycalolide B. We also demonstrated that the depolymerizing effect of bistheonellide A or mycalolide B is irreversible. Bistheonellide A increased, while swinholide A decreased, the rate of nucleotide exchange in G-actin, suggesting that binding of these toxins induces different conformational changes in the actin molecule. These results suggest that bistheonellide A intervenes between two actin molecules, forms a tertiary complex with each of its side chains bound to G-actin, and inhibits polymerization by sequestering G-actin from incorporation into F-actin. A difference in structure at the end of the side chain between dimeric macrolides and mycalolide B may account for the weak severing activity of the former.
Saito
S Y
SY
Department of Veterinary Pharmacology, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113.
Watabe
S
S
Ozaki
H
H
Kobayashi
M
M
Suzuki
T
T
Kobayashi
H
H
Fusetani
N
N
Karaki
H
H
D000199:Actins / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001704:Biopolymers; D018942:Macrolides / Q000494:pharmacology*; D008387:Marine Toxins / Q000494:pharmacology*; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism; D011485:Protein Binding; D011817:Rabbits
D000199:Actins; D001704:Biopolymers; D018942:Macrolides; D008387:Marine Toxins; C104924:bistheonellide A; D000255:Adenosine Triphosphate; C086235:swinholide A