Fig. 2: X-ray and cryo-EM structures of P1.

a Ribbon representation, with three 90° apart views, of the complete extracellular region of P1. The large N-terminal domain is organized around a seven-blade β-propeller (light orange) from where the crown (green) emerges. The C-terminal domain (cyan) is immediately followed by a predicted transmembrane helix, which requires the proximity of this domain to the cell membrane. b P1 map densities from cryo-EM (left panels) and X-ray crystallography (right panels). Insets show representative regions from the N-terminal domain (top) and the C-terminal domain (bottom). The quality of the cryo-EM density provides the clear identification of residues in the N-terminal domain (at an estimated resolution of 2.9 Å). On the contrary, the C-terminal domain is poorly defined in the cryo-EM map, indicating high flexibility with respect to the N-terminal domain. The core of the N-terminal domain and, especially, the C-terminal domain are well defined in the X-ray map, while the very top of the N-terminal domain presents high-temperature factors and was difficult to trace. c Topology of the β-propeller in P1. Loops contributing to the crown are colored green. Disordered loops are indicated with black dots and the stretch of serines (the AGT repeats) with a red cross. Strands and loops are not in scale.