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. 2015 Jun 29;290(37):22494–22506. doi: 10.1074/jbc.M115.670166

FIGURE 7.

FIGURE 7.

Models of steady state actin turnover in the presence of INF2 and profilin. Actin subunits are colored dark red for ATP- or ADP-Pi state, and light red for ADP state. INF2-FFC in blue, yellow, and black (for FH1, FH2, and C terminus, respectively). Profilin is shown in green (wild type) or gray (Y6D mutant). A, actin alone. 1) ATP-bound actin adds to the barbed end (10 μm−1 s−1). 2) The incorporated actin hydrolyzes its ATP and releases the phosphate product in a random manner (0.002 s−1). 3) Net dissociation of ADP-actin at the pointed end (0.06 s−1). 4) Nucleotide exchange: the dissociated ADP-actin monomer releases ADP slowly (0.009 s−1) and then binds ATP, enabling another round of barbed end addition. B, actin with INF2-FFC (2:1 ratio). 1) ATP-bound actin adds to the INF2-bound barbed end (3.6 μm−1 s−1). 2) INF2 side binding to filament (calculated rate 0.0014 μm−1 s−1). 3) ATP hydrolysis and phosphate release (unknown in presence of bound INF2). 4) INF2-mediated filament severing (rate unknown). 5) Release of ADP-actins from WH2 of INF2 after severing (rate unknown). 6) nucleotide exchange (0.003 s−1). C, actin with INF2-FFC and profilin (2:1:4 ratio). 1) Profilin-bound ATP-actin adds to the INF2-bound barbed end (6.9 μm−1 s−1). 2) INF2 side binding to filament (calculated rate, 0.0014 μm−1 s−1). 3) ATP hydrolysis and phosphate release (unknown in presence of bound INF2). 4) INF2-mediated filament severing (rate unknown). 5) release of ADP-actins from WH2 of INF2 after severing (rate unknown). 6) Profilin-enhanced nucleotide exchange (1.4 s−1). D, actin with INF2-FFC and profilin-Y6D (2:1:4 ratio). 1) Profilin-bound ATP-actin adds to the INF2-bound barbed end but is not facilitated by the profilin-FH1 interaction (3.6 μm−1 s−1). 2) INF2 side binding to filament (calculated rate 0.0014 μm−1 s−1). 3) ATP hydrolysis and phosphate release (unknown in presence of bound INF2). 4) INF2-mediated filament severing (rate unknown). 5) release of ADP-actins from WH2 of INF2 after severing (rate unknown). 6) Profilin-enhanced nucleotide exchange (1.4 s−1).