Pairwise sequence comparison of the core phosphatase sequences shows
that the sequences cluster into four distinct groups. The sequences
within each group show greater similarity to each other than they do
to other phosphatase sequences. The groupings are: PP1-like
sequences, PP2A-like and PP2B-like. Human PP5 ( A.E. McPartlin, H.M.
Barker and P.T.W. Cohen, in preparation) and S.cerevisiae PPT
[36]
form a fourth
distinct group which shows least similarity to all other phosphatase
sequences in this region. Table 1 lists the range of sequence identity
seen within and between the classes in the phosphatase domain shown in
Figure 1. The three major groups are consistent with known
physico-chemical properties of these phosphatases. In addition
PP2B-like structures all possess long C-terminal extensions that bind
and calmodulin, whilst all PP2A-like and most PP1-like structures
have no long N or C-terminal extensions. The exceptions in the
PP1-like group are S.cerevisiae PPQ [37] PPZ1
and PPZ2 [38]
which have long serine rich N-terminal extensions. PP5 and PPT
possess long N-terminal extensions with a repeat structure. The
clustering performed here is sufficient to provide a guide for
structure prediction. However, more detailed considerations of the
evolutionary relationships between the full-length serine/threonine
phosphatases will be presented elsewhere.
Figure 1 illustrates a multiple alignment of the common core of the eukaryotic phosphatase sequences; the four groupings are delineated by horizontal lines. The boxing and shading reflects conservation of physico chemical properties within each group and across the entire set of sequences (see legend for details).