Structure of Pyrococcus furiosus Hjm. (A) The Form 2 apo structure is shown as a ribbon representation with a color spectrum from blue (N-terminus) to red (C-terminus). (B) and (C) Omit |F
c| maps (2.5 σ) for ADP in Form 1 (B) and AMPPCP in Form 2 (C) are shown with the final models. (D) Comparison of the nucleotide binding sites between Hjm and Hel308. Hjm is represented in blue, and the key residues interacting with the ATP analog are highlighted. Segments of A. fulgidus Hel308 (pink) should undergo structural changes to bind the nucleotide, while S. solfataricus Hel308 (green) could bind the nucleotide with slight rearrangements in the pocket. A. fulgidus Hel308 residues, which should sterically clash with the nucleotide, are indicated by magenta arrows.