Figure 13
From: Structural and evolutionary bioinformatics of the SPOUT superfamily of methyltransferases
Possible origins of the knot. A) Contemporary knotted SPOUT fold, exemplified by E. coli YbeA (1ns5). B) Putative ancestral structure, 'unknotted' by deletion of an α/β unit. C) Alternative putative ancestral structure, 'unknotted' by circular permutation, i.e. linking 'old' termini and cutting the knot to create new termini. Protein sequence is colored from blue (N-terminus) to red (C-terminus).