Cyanobacterial PPP family protein phosphatases possess multifunctional capabilities and are resistant to microcystin-LR.
The structural gene for a putative PPP family protein-serine/threonine phosphatase from the microcystin-producing cyanobacterium Microcystis aeruginosa PCC 7820, pp1-cyano1, was cloned. The sequence of the predicted gene product, PP1-cyano1, was 98% identical to that of the predicted product of an open reading frame, pp1-cyano2, from a cyanobacterium that does not produce microcystins, M. aeruginosa UTEX 2063. By contrast, PP1-cyano1 displayed less than 20% identity with other PPP family protein phosphatases from eukaryotic, archaeal, or other bacterial organisms. PP1-cyano1 and PP1-cyano2 were expressed in Escherichia coli and purified to homogeneity. Both enzymes exhibited divalent metal dependent phosphohydrolase activity in vitro toward phosphoserine- and phosphotyrosine-containing proteins and 3-phosphohistidine- and phospholysine-containing amino acid homopolymers. This multifunctional potential also was apparent in samples of PP1-cyano1 and PP1-cyano2 isolated from M. aeruginosa. Catalytic activity was insensitive to okadaic acid or the cyanobacterially produced cyclic heptapeptide, microcystin-LR, both potent inhibitors of mammalian PP1 and PP2A. PP1-cyano1 and PP1-cyano2 displayed diadenosine tetraphosphatase activity in vitro. Diadenosine tetraphosphatases share conserved sequence features with PPP family protein phosphatases. The diadenosine tetraphosphatase activity of PP1-cyano1 and PP1-cyano2 confirms that these enzymes share a common catalytic mechanism.
Shi
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Department of Biochemistry, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, USA.
Carmichael
W W
WW
Kennelly
P J
PJ
D000227:Adenine Nucleotides / Q000378:metabolism; D000595:Amino Acid Sequence; D002384:Catalysis; D003001:Cloning, Molecular; D000458:Cyanobacteria / Q000235:genetics*; D004926:Escherichia coli; D005798:Genes, Bacterial; D006863:Hydrogen-Ion Concentration; D008387:Marine Toxins; D052998:Microcystins; D008969:Molecular Sequence Data; D010456:Peptides, Cyclic / Q000494:pharmacology*; D010749:Phosphoprotein Phosphatases / Q000737:chemistry / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism*
D000227:Adenine Nucleotides; D008387:Marine Toxins; D052998:Microcystins; D010456:Peptides, Cyclic; D010749:Phosphoprotein Phosphatases; C057862:cyanoginosin LR