Fig. 1.

(A) Structural alignment of β-(P-loop)-α motifs of different P-loop NTPase (the canonical Walker-A residues: G₁, G₂, and G₃ are in pink, K₄ in black, and [T/S]₅in white; G1-XX-G2-X-G3-K4-(S/T)5). (B) Sequence logo representing the inferred ancestral β-(P-loop)-α profile. (C) Sequence alignment of the most probable ancestral β-(P-loop)-α sequence and of the N-terminal segments of the PLoop designs. (D) Schematic representation of the secondary structure and topology of the PLoop designs. Helices are represented by rectangles or circles, strands by arrows or triangles, and the P-loops by pink segments. The flanking strand of the β-(P-loop)-α segment is in blue and the helix in red.