Swaposins - circular permutations within genes encoding saposin homologs
Christopher P. Ponting & Robert B. Russell
From Trends In Biochemical Sciences, 20, 179-180, 1995.
The paper reported a clear example of a circularly permutated protein sequence, where
both protein and gene sequences had been permuted in one homologue relative to another.
A protein can be described as a
circular permutation of another if one has to swap the order of N- and C-
terminal sequence fragments to get the correct alignment.
To the best of our knowledge, the example found within the saposin family is the first of its kind.
You can see an alignment (PostScript) of
the sequences for this family of proteins (Saposins), and a
picture of how
permutation could be tolerated within a hypothetical saposin structure simply by the
re-location of the N- and C- termini to a different location.