H8-L-H9 conformation in non-proteobacterial GluRSs: δ/γ-[>>t] conformations
Two proteins, Bbu -GluRS and Mtu -GluRS, displayed the [>>t ] conformation, with K289 (BBU) and D294 (MTU) side-chains positions overlapping with D273 ofEco -GluRS. The Type II’ β-turn sequence of Eco -GluRS (HGDQ) is replaced by 291IADDH in Mtu -GluRS and286YDDKR in Bbu -GluRS. The sequence stretch292ADDH in Mtu -GluRS forms a Type I β-turn (φD293: -78.7, ψD293: -17.2; φD294: -104.3, ψD294: 3.3) where the side-chains of D294 and D273 (Eco -GluRS) overlap. With a 13-residue loop and a Type I β-turn at the center, this is similar to the conformation β-[>>t ] observed for Pae -GluRS. On the other hand, the sequence stretch YDDKR inBbu -GluRS forms an α-turn (YCA-RCA distance: 6.9 Å; φD287: -133.1, ψD287: 11.6; φD288: 62.8, ψD288: 8.4; φK289: -112.2, ψK289: -59.4), with the side-chain of K289 oevrlapping with D273 (Eco -GluRS). With a 13-residue loop and an α-turn at the center, we call this conformation δ-[>>t ] (δ-type towards tRNA).