Sequence and structure of Mistic homologues. (a) Sequence alignment of the four 84-residue Mistic homologues is shown, as well as the leading 26 amino acids found only in B. subtilis Mistic. Residues are colored by their degree of conservation, as indicated. Below the alignment, secondary structural elements are depicted as well as residue accessibility. Pairs of compensating mutations related to conservation of acidic residues are indicated by purple brackets. (b) Unconserved residues (numbered 1–9) and weakly conserved residues (a-e) are mapped to the NMR structure of Mistic (colored as above) revealing their restriction to flexible, loop regions of the protein. The core of the structure (grey oval) is virtually devoid of significant alterations. This pattern suggests that the overall structural fold of the protein, less the N-terminal helix (α1, grey), is conserved between the four homologues. Positions of compensating mutational pairs for anionic residues are indicated by purple arrows revealing their close proximity in the folded protein.