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4) Symposium Posters | Main^

P7. W0122 Structure of an Anti-parallel Actin Dimer.

2002 Annual American Crystallographic Association Meeting, San Antonio, Texas.
Christian Banchs, Michael Bubb, Lakshmanan Govindasammy, Elena Yarmola, Thayumanasamy Somasundaram, Michael Chapman, Sergey Vorobiev, Steven Almo, Mavis Agbandje-McKnna, and Robert McKenna.
Biochemistry and Molecular Biology, University of Florida College of Medicine, PO Box 100245, Gainesville, FL 32610-0245 USA.

Polylysine is a potent nucleator of actin filament growth in vitro. Here we show that similar to de novo nucleation and gelsolin-induced nucleation, an anti-parallel dimer forms as an intermediate during polylysine stimulated actin polymerization. Latrunculin A, a marine natural product that inhibits actin polymerization, arrests polylysine-induced nucleation at the level of the anti-parallel dimer, resulting in accumulation of dimer. Latrunculin A-polylysine-actin dimers were crystallized, and the structure reported here confirms the anti-parallel orientation of actin subunits. Remarkably, the structure reveals that the mobile DNase I binding loop of a third actin subunit can be stabilized in the interface between the two subunits of the dimer, with a similarsurface of interaction to that in current models of an actin filament. This provides a potential explanation for the paradoxical nucleation of actin filaments with exclusively parallel subunits by a dimer containing anti-parallel subunits.

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