NMR solution structures of ctNsa2 domains. (A) NMR structure of recombinant ctNsa2-C (168–261 aa) adopts an Rps8 (eS8)-like six-stranded β-barrel fold. A structural similarity search of the protein databank performed with the DALI server identified the 40S ribosomal protein Rps8 (PDB accession no. 3U5C, chain I) from S. cerevisiae (S288c; sequence identity of 22%, Z score = 5.3, RMSD 3.7 Å) as structurally similar to ctNsa2 168–261 aa. The right panel shows the structure of an archaeal Rps8 taken from the PDB (accession no. 3J43). The six-stranded β-barrel fold is shown in green; variable insertions are shown in yellow, orange, and purple. (B) Multiple sequence alignment including Nsa2, archaeal Rps8 (aRps8), and eukaryotic Rps8 (eRps8). Secondary structure elements are indicated for ctNsa2 on top (derived by NMR) and S. cerevisiae Rps8 (PDB accession no. 3U5C) below. (C) Representative NMR structures of ctNsa2-N, determined by CS-Rosetta, show a common fold composed of one short N-terminal α-helix followed by two longer α-helices (H1 and H2). Multiple structures that differ in the packing and orientation of helix 2 reflect the disorder in the linker connecting the helices and the dynamic nature of Nsa2-N in solution.