CONSERVED SEQUENCE MOTIFS AMONG BACTERIAL, EUKARYOTIC, AND ARCHAEAL PHOSPHATASES THAT DEFINE A NEW PHOSPHOHYDROLASE SUPERFAMILY

Members of a new molecular family of bacterial nonspecific acid phosph atases (NSAPs), indicated as class C, were found to share significant sequence similarities to bacterial class B NSAPs and to some plant aci d phosphatases, representing the first example of a family of bacteria l NSAPs that has a relatively close eukaryotic counterpart. Despite th e lack of an overall similarity, conserved sequence motifs were also i dentified among the above enzyme families (class B and class C bacteri al NSAPs, and related plant phosphatases) and several other families o f phosphohydrolases, including bacterial phosphoglycolate phosphatases , histidinol-phosphatase domains of the bacterial bifunctional enzymes imidazole-glycerolphosphate dehydratases, and bacterial, eukaryotic, and archaeal phosphoserine phosphatases and threalose-6-phosphatases. These conserved motifs are clustered within two domains, separated by a variable spacer region, according to the pattern [FILMAVT]-D-[ILFRMV Y]-D-[GSNDE]-[TV]-[ILVAM]- [ATSVILMC]-X-{YFWHKR}-X-{YFWHNQ}-X(102, 191 )- {KRHNQ}-G-D-{FYWHILVMC}-{QNH}-{FWYGP}-D- {PSNQYW}. The dephosphoryl ating activity common to all these proteins supports the definition of this phosphatase motif and the inclusion of these enzymes into a supe rfamily of phosphohydrolases that we propose to indicate as ''DDDD'' a fter the presence of the four invariant aspartate residues. Database s earches retrieved various hypothetical proteins of unknown function co ntaining this or similar motifs, far which a phosphohydrolase activity could be hypothesized.