Formin Leaky Cap Allows Elongation in the Presence of Tight Capping Proteins
Abstract
Formins, characterized by formin homology domains FH1 and FH2, are required to assemble certain F-actin structures including actin cables, stress fibers, and the contractile ring. FH1FH2 in a recombinant fragment from a yeast formin (Bni1p) nucleates actin filaments in vitro [1, 2]. It also binds to the filament barbed end where it appears to act as a "leaky" capper, slowing both polymerization and depolymerization by ∼50% [3]. We now find that FH1FH2 competes with tight capping proteins (including gelsolin and heterodimeric capping protein) for the barbed end. We also find that FH1FH2 forms a tetramer. The observation that this formin protects an end from capping but still allows elongation confirms that it is a leaky capper. This is significant because a nucleator that protects a new barbed end from tight cappers will increase the duration of elongation and thus the total amount of F-actin. The ability of FH1FH2 to dimerize probably allows the formin to walk processively with the barbed end as the filament elongates.
- Publication:
-
Current Biology
- Pub Date:
- October 2003
- DOI:
- 10.1016/j.cub.2003.09.057
- Bibcode:
- 2003CBio...13.1820Z