Figure 1.

Structure-guided sequence alignment of four iNAs and six non-iNAs based on conserved active site residues (violet) reveals two iNA-specific loop insertions: nine amino acids residues 138–147 (red) preceding the conserved aspartic acid D151 and the Ca²⁺ ion binding site between residues 320–350 (grey). The focus is on the catalytic domains of NAs, therefore parts of non-catalytic domains (green) are not shown (residues 1–199 in non-iNA Sp and residues 414–634 in non-iNA Tc).