Figure 1.
Schematic representation of a circular permutation in two proteins.
The first protein (outer circle) has the sequence a-b-c. After the permutation the second protein (inner circle) has the sequence c-a-b. The letters N and C indicate the location of the amino- and carboxy-termini of the protein sequences and how their positions change relative to each other.
Figure 2.
Two proteins that are related by a circular permutation.
Concanavalin A (left), from the Protein Data Bank (PDB), 3cna and peanut lectin (right), from PDB 2pel, which is homologous to favin. The termini of the proteins are highlighted by blue and green spheres, and the sequence of residues is indicated by the gradient from blue (N-terminus) to green (C-terminus). The 3D fold of the two proteins is highly similar; however, the N- and C- termini are located on different positions of the protein [1].
Figure 3.
The permutation by duplication mechanism for producing a circular permutation.
First, a gene is duplicated in place. Next, start and stop codons are introduced, resulting in a circularly permuted gene.
Figure 4.
Suggested relationship between saposin and swaposin.
They could have evolved from a similar gene [15]. Both consist of four alpha helices with the order of helices being permuted relative to each other.
Figure 5.
The fission and fusion mechanism of circular permutation.
Two separate genes arise (potentially from the fission of a single gene). If the genes fuse together in different orders in two orthologues, a circular permutation occurs.
Figure 6.
Transhydrogenases in various organisms can be found in three different domain arrangements.
In cattle, the three domains are arranged sequentially. In the bacteria E. coli, Rb. capsulatus, and R. rubrum, the transhydrogenase consists of two or three subunits. Finally, transhydrogenase from the protist E. tenella consists of a single subunit that is circularly permuted relative to cattle transhydrogenase [20].
Table 1.
Algorithms for comparing pairs of circularly permuted proteins.