Characterization of the major phosphofructokinase-dephosphorylating protein phosphatases from Ascaris suum muscle

CLONING AND NUCLEOTIDE SEQUENCE OF A FULL-LENGTH cDNA ENCODING ASCARIS SUUM PHOSPHOFRUCTOKINASE

The nucleotide sequence of a full-length cDNA encoding phosphofructokinase (PFK) enzyme from the parasitic nematode Ascaris suum was determined. The entire sequence of 2,653 bases comprises a single open reading frame of 2,452 bases and a noncoding region of 201 bases after the stop codon. The mature protein contains 812 amino acids and has a molecular mass of 90,900 Da. The amino acid sequences of several peptides derived from the purified protein show excellent correspondence with the translated nucleotide sequence. Comparison of the amino acid sequence of the protein with those of 3 other worms as well as those of human, rabbit, and bacterial enzymes reveals highly conserved regions interrupted with stretches of lesser sequence similarity. Analyses of the subunit primary structure reveal, as in other eukaryotic PFKs, that the amino-terminal half is homologous to the carboxy-terminal half, supporting the hypothesis that the PFK gene evolved by duplication of the prokaryotic gene and that the allosteric sites arose by mutations at the catalytic site. The location of the phosphorylation site is unique and different compared with other PFKs and plays a key role in regulation of the enzyme activity. Structural motifs such as the putative substrate and effector binding domains and also the key amino acids involved therein are clearly identified by alignment of all the PFK protein sequences.

Activation by phosphorylation of phosphofructokinase from the annelid Lumbricus terrestris and comparison of phosphorylated sites in invertebrate phosphofructokinases

Purified phosphofructokinase from the earthworm Lumbricus terrestris was phosphorylated in vitro by the catalytic subunit of cAMP-dependent protein kinase from the same organism to an extent of approx. 0.5 mol/mol of subunit. Activation of the enzyme occurred in parallel to the incorporation of covalently bound phosphate and was reversed by the action of the catalytic subunit of protein phosphatase 2A. Phosphorylation decreased the co-operativity of fructose 6-phosphate saturation in the presence of inhibitory concentrations of ATP, and increased the apparent Vmax obtained with saturating concentrations of the activators 5'-AMP and fructose 2,6-bisphosphate. The phosphorylated sites of phosphofructokinase from L. terrestris and from two molluscs (Helix pomatia and Mytilus edulis) were sequenced and shown to exhibit distinct similarity to sequences located near to the N-terminus of nematode phosphofructokinases [Klein, Olson, Favreau, Wintertowed, Hatzenbuhler, Shea, Nulf and Geary (1991) Mol. Biochem. Parasitol. 48, 17-26.

Conservation, evolution, and specificity in cellular control by protein phosphorylation

The glycolytic control enzyme phosphofructokinase from the parasitic nematode Ascaris lumbricoides is regulated by reversible phosphorylation. The enzyme is phosphorylated by an atypical cyclic adenosine monophosphate (cAMP)-dependent protein kinase whose substrate specificity deviates from that of the mammalian protein kinase. This variation is explained by structural peculiarities on the surface part of the catalytic groove of the protein kinase. Also, the protein phosphatases responsible for the reversal of phosphorylation appear to act specifically in glycolysis and are different from those participating in regulation of glycogenolysis.

The Saccharomyces cerevisiae gene PPH3 encodes a protein phosphatase with properties different from PPX, PP1 and PP2A

A clone encoding the catalytic subunit of a protein phosphatase from Saccharomyces cerevisiae was isolated. Except for replacement of IIe-245 by Met the structure of the phosphatase was identical to that encoded by PPH3 (Ronne, H., Carlberg, M., Hu, G. Z. and Nehlin, J. O. (1991). Mol. Cell. Biochem. 11, 4876-4884) and exhibited 63% sequence identity to PPX cloned from a rabbit liver cDNA library (Brewis, N.D., Street, A.J., Prescott, A.R. and Cohen, P.T.W. (1993). EMBO J. 12, 987-996). Expression of active enzyme was achieved in Escherichia coli mutants which were generated by a genetic selection based on functional complementation of bacterial phosphoserine phosphatase. Though some of the properties of PPH3 resembled those of protein phosphatase 2A and PPX, others were different. PPH3 exhibited lower sensitivity against inhibition by okadaic acid, showed different substrate specificity and required a divalent cation (Mn2+ was preferred before Mg2+ and Ca2+) for activity when assayed with phospho-histone as a substrate. However, 25% of maximum activity was observed in the absence of divalent cations when the peptide LRRAS(P)LG was used as substrate. The PPH3-protein was also identified by chromatography of extracts from S. cerevisiae on DEAE-cellulose. Protein immunoreactive with an antiserum raised against the non-conserved N-terminal 53 amino acids of PPH3 was coeluted with a single peak of LRRAS(P)LG dephosphorylating activity.

Phosphoprotein patterns in Onchocerca volvulus developmental stages

Living females and microfilariae of Onchocerca volvulus incubated in culture medium containing [32P]orthophosphate were observed to phosphorylate their proteins rapidly. Patterns of phosphoproteins in extracts from these labelled parasites were compared after two dimensional electrophoresis and autoradiography. Protein extracts from eggs, microfilariae and adult females of O. volvulus were phosphorylated in the presence of [gamma-32P]ATP, magnesium acetate, and added cyclic AMP-dependent protein kinase or the endogenous protein kinase present in the extracts. Patterns of phosphoproteins were compared after separation by single and two-dimensional gel electrophoresis followed by autoradiography. Common phosphopeptide bands were observed when phosphorylated extracts from adult females, microfilariae and eggs were compared. However, extracts from eggs displayed unique phosphorylated polypeptides of M(r) 30,000 and 34,000 that were absent from the extracts from microfilariae. Furthermore, two phosphorylated polypeptides of M(r) 47,000 and 76,000 were detected in extracts from microfilariae but not from eggs. These results indicate that O. volvulus parasites may phosphorylate different proteins at different stages of their development.