From sequence comparisons and crystallographic data analysis it has been shown
[1,2,3,4,5,6] that an appreciable proportion of proteins that bind ATP or GTP
share a number of more or less conserved sequence motifs. The best conserved
of these motifs is a glycine-rich region, which typically forms a flexible
loop between a β-strand and an α-helix. This loop interacts with one of
the phosphate groups of the nucleotide. This sequence motif is generally
referred to as the 'A' consensus sequence  or the 'P-loop' .
There are numerous ATP- or GTP-binding proteins in which the P-loop is found.
We list below a number of protein families for which the relevance of the
presence of such motif has been noted:
DNA mismatch repair proteins mutS family (See <PDOC00388>).
Bacterial type II secretion system protein E (see <PDOC00567>).
Not all ATP- or GTP-binding proteins are picked-up by this motif. A number of
proteins escape detection because the structure of their ATP-binding site is
completely different from that of the P-loop. Examples of such proteins are
the E1-E2 ATPases or the glycolytic kinases. In other ATP- or GTP-binding
proteins the flexible loop exists in a slightly different form; this is the
case for tubulins or protein kinases. A special mention must be reserved for
adenylate kinase, in which there is a single deviation from the P-loop
pattern: in the last position Gly is found instead of Ser or Thr.
PROSITE is copyright. It is produced by the SIB Swiss Institute
Bioinformatics. There are no restrictions on its use by non-profit
institutions as long as its content is in no way modified. Usage by and
for commercial entities requires a license agreement. For information
about the licensing scheme send an email to
or see: prosite_license.html.