Open AccessCharacterization of a Novel Mammalian Phosphatase Having Sequence Similarity to Schizosaccharomyces pombe PHO2 and Saccharomyces cerevisiae PHO13
Author(s) -
MacKevin I. Ndubuisil,
Benjamin H. Kwok,
Jonathan Vervoort,
Brian D. Koh,
Mikael Elofsson,
Craig M. Crews
Publication year - 2002
Publication title -
biochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.43
H-Index - 253
eISSN - 1520-4995
pISSN - 0006-2960
DOI - 10.1021/bi0255064
Subject(s) - phosphatase , schizosaccharomyces pombe , biochemistry , saccharomyces cerevisiae , yeast , enzyme , chemistry , divalent , peptide sequence , okadaic acid , escherichia coli , dephosphorylation , alkaline phosphatase , microbiology and biotechnology , biology , gene , organic chemistry
p34, a specific p-nitrophenyl phosphatase (pNPPase) was identified and purified from the murine cell line EL4 in a screen for the intracellular molecular targets of the antiinflammatory natural product parthenolide. A BLAST search analysis revealed that it has a high degree of sequence similarity to two yeast alkaline phosphatases. We have cloned, sequenced, and expressed p34 as a GST-tagged fusion protein in Escherichia coli and an EE-epitope-tagged fusion protein in mammalian cells. Using p-nitrophenyl phosphate (pNPP) as a substrate, p34 is optimally active at pH 7.6 with a K(m) of 1.36 mM and K(cat) of 0.052 min(-1). Addition of 1 mM Mg(2+) to the reaction mixture increases its activity by 14-fold. Other divalent metal ions such as Co(2+) and Mn(2+) also stimulated the activity of the enzyme, while Zn(2+), Fe(2+), and Cu(2+) had no effect. Furthermore, both NaCl and KCl enhanced the activity of the enzyme, having maximal effect at 50 and 75 mM, respectively. The enzyme is inhibited by sodium orthovanadate but not by sodium fluoride or okadaic acid. Mutational analysis data suggest that p34 belongs to the group of phosphatases characterized by the sequence motif DXDX(T/V).