Structure and sequence comparison of the EcGspS crystal structure (pdb: 2ioa; A) and the modeled LmTryS structure (B).
Both structures contain ADP, the Gsp analogue (shown as sticks with carbons in yellow) and two Mg2+ ions (green balls). The yellow circle highlights an additional pocket in the TryS model which results from sequence differences (C). The green surfaces (I and II) indicate flexible loop regions that were not visible in the LmTryS crystal structure (pdb:2vps): In the EcGspS structure (A) region I (Gly 242 to Pro 249) does not offer any additional binding site near the spermidine moiety of the Gsp analogue, while in the LmTryS model (B) the corresponding loop (Gly250 to 262; marked red in C) builds part of the additional binding pocket. II shows the borders of the ATP Grasp fold loop (Pro534 to Gln563 in EcGspS and Val551to Asn579 in LmTryS, respectively). The loop was removed in both structures to demonstrate the positions of ADP and Mg2+.