Figure 3: Pulling forces increase the elongation rate of filaments from mDia1(FH1FH2).
From: Formin mDia1 senses and generates mechanical forces on actin filaments
(a) Traces for two different filaments, elongating from 1 μM ATP-actin and 4 μM profilin. One filament is exposed to a flow velocity of 101 μm s−1 (blue diamonds) while the other is exposed to a flow velocity of 54 μm s−1 (red open circles) with a temporary increase to 215 μm s−1 (red bullets). Each actin subunit contributes to 2.7 nm of the filament length. (b) Resulting elongation rate versus force for each filament. (c) Average data from traces of 8–14 filaments for each profilin–actin concentration: 0.5 μM (blue diamonds, n=9 filaments), 1 μM (triangles, n=8), 2 μM (squares, n=14) and 3 μM (bullets, n=11), each with a 3-μM excess of profilin. Error bars are s.d. All data were obtained with mDia1(FH1FH2) anchored by the FH2 domain, except grey data points where the anchor was on the FH1 domain. Open symbols correspond to control experiments with unanchored formins at the barbed end of filaments grown from anchored spectrin-actin seeds. Lines are fits of the data by equation (2), performed with p0 and the plateau velocity kon(C−Cc) as free parameters for each set of data. Inset: plot of the resulting plateau values (black symbols) at high force, as a function of profilin–actin concentration, compared with elongation rates in the absence of force (open symbols). Lines are linear fits.
