Figure 6. The Arp3 C terminus is an allosteric molecular switch that locks the complex in the inactive (splayed) conformation.

(a) Cartoon depicting proposed conformational link between the ATP-binding cleft, the barbed end groove and the C terminus of Arp3. Dotted red lines indicate widths of nucleotide-binding cleft (NBC) and barbed end groove. The tip (T) and base (B) of the Arp3 C terminus are indicated. (b) Time course of crosslinking assays containing 1 μM wild-type ScArp2/3 complex with or without 100 μM Mg²⁺-ATP. (c) Quantification of 5-min short-pitch crosslinking for reactions containing 1 μM wild type or ATP-binding pocket mutation complexes with either 1 μM EDTA or 200 μM Mg²⁺-ATP. (d) Quantification of 1-min short-pitch crosslinking assays of wild type or splayed interface mutations with or without 200 μM Mg²⁺-ATP. Error bars in c and d show s.e. for three reactions.