Crystals of the Arp2/3 complex in two new space groups with structural information about actin-related protein 2 and potential WASP binding sites

Co‐crystals of the bovine Arp2/3 complex with the CA motif from N‐WASP in two new space groups were analyzed by X‐ray diffraction. The crystals in the orthorhombic space group P212121 contained one complex per asymmetric unit, with unit‐cell parameters a = 105.48, b = 156.71, c = 177.84 Å, and diffracted to 3.9 Å resolution. The crystals in the tetragonal space group P41 contained two complexes per asymmetric unit, with unit‐cell parameters a = b = 149.93, c = 265.91 Å, and diffracted to 5.0 Å resolution. The electron‐density maps of both new crystal forms had densities for small segments of subdomains 1 and 2 of Arp2. Both maps had density at the binding site on Arp3 for the C‐terminal EWE tripeptide from N‐WASP and a binding site proposed for the C motif of N‐WASP in the barbed‐end groove of Arp2. The map from the tetragonal crystal form had density near the barbed end of Arp3 that may correspond to the C helix of N‐WASP. The noise levels and the low resolution of the maps made the assignment of specific molecular structures for any of these CA peptides impossible.