7 Å and 5.5 Å (Figure 3A); this close apposition is similar to that found in homomeric dimer assemblies for the GluR6, GluR6Δ1, and GluR7 ATDs, for which the corresponding Cα positions are separated by 5.5, 5.8 and 5.6 Å, while for the KA2 homodimer assembly these residues are separated by 10.7 Å. In addition to this movement, analysis of the extent of domain closure indicates that the KA2 clam shell in the heterodimer is closed by 4.5°–7.5° compared to KA2 subunits in homodimer crystal structures, while the GluR6 subunit is closed

BMN 673 supplier by 4.2°–6.5° when compared to GluR6 homodimer structures. Solvent accessible surface analysis of

the GluR6/KA2 heterodimer interface reveals a total buried area of 2953 Å2 with the KA2 protomer contributing 1496 Å2, a gain of 536 Å2 compared to the KA2 homodimer assembly (Figure 2D). For the GluR6 subunit, although there is little change in buried surface area in the homodimer and heterodimer assemblies, local rearrangements produce key changes in intersubunit contacts. The R1 interface in both the GluR6/KA2 heterodimer and in the GluR6 homodimer is formed primarily by a close apposition of α helices B and C from each protomer. For both subunits, loop 3, which has been proposed to be a major determinant of subtype-specific assembly mediated by

iGluR ATDs (Jin et al., 2009), selleck chemicals projects into the heterodimer interface and is anchored by intramolecular disulfide bonds between Cys65 or Cys64 on α-helix B, and Cys316 or Cys315, for GluR6 and KA2, respectively (Figures only 3, S4A, and S4B). Of note, we observe novel intersubunit interactions in the heterodimer assembly, which are absent in GluR6 and KA2 homodimer structures, and which involve loop 3. Due to formation of a hydrogen bond between the KA2 Tyr57 OH group and the GluR6 main chain nitrogen of Asn317, the tip of loop 3 in the GluR6 subunit undergoes a conformational change in the heterodimer assembly (Figure 3A). This results in a 5Å movement of the Asn317 side chain, which dips down into the heterodimer interface and becomes trapped between the Asp61 and Tyr57 side chains near the base of α-helix B in the KA2 subunit. Due to replacement of Tyr57 by Phe58, in the GluR6 homodimer this hydrogen bond is absent. Additional interactions made by the KA2 protomer at the R1 interface, which are unique to the heterodimer structure, result from movement of α helices B and C toward the central axis of dimer formation, generating a series of contacts with the GluR6 protomer that are absent in KA2 homodimers.