Rapid purification and N-terminal sequencing of a potato tuber cyclic nucleotide binding phosphatase

Cyclic AMP affinity purification and ESI-QTOF MS-MS identification of cytosolic glyceraldehyde 3-phosphate dehydrogenase and two nucleoside diphosphate kinase isoforms from tobacco BY-2 cells

The soluble protein fraction of tobacco bright yellow 2 cells contained adenosine 3',5'-cyclic monophosphate (cAMP)-binding activity, detected with both a conventional binding assay and a surface plasmon resonance biosensor. A cAMP-agarose-based affinity purification procedure yielded three proteins which were identified by mass spectrometry as glyceraldehyde 3-phosphate dehydrogenase (GAPDH) and two nucleoside diphosphate kinases (NDPKs). This is the first report describing an interaction between cAMP and these proteins in higher plants. Our findings are discussed in view of the reported role of the interaction of cAMP with GAPDH and NDPK in animals and yeast. In addition, we provide a rapid method to isolate both proteins from higher plants.

A histidine thiol 100 kDa, tetrameric acid phosphatase from lentil, Lens esculenta, seeds with the characteristics of protein tyrosine phosphatases

A non-specific acid phosphatase (APase) hydrolysing L-tyrosine-O-phosphate and 3'-AMP was purified to electrophoretic homogeneity from mature lentil seeds with apparent native molecular mass of 100 kDa and subunit molecular mass of 24 kDa. These activities appear to reside on the same protein which shows a single band in native and SDS-PAGE. The pH optimum is 5.5, while the K(m) (mM) and V(max) (micromoles/min/mg protein) for p-nitrophenyl phosphate (pNPP) are 0.7 and 9.2 and for L-tyrosine-O-phosphate 1.4 and 10.1, respectively, at 30 degrees C and for 3'-AMP, 2 and 4.4 at 37 degrees C. The protein also hydrolyses other phosphomonoesters to a lesser extent. L-Tyrosine-O-phosphate, 3'-AMP and pNPP hydrolysis is potently inhibited by micromolar orthovanadate and also to nearly the same extent by sodium fluoride, potassium tartrate and metal ions. Histidine and cysteine are likely to be involved in the catalysis. Thermal inactivation studies indicate that the active site conformations for pNPP and 3'-AMP hydrolytic activities are different. The enzyme shows the characteristics of the animal protein tyrosine phosphatase.

Oligosaccharide and polypeptide homology of lupin (Lupinus luteus L.) acid phosphatase subunits

Peptide mapping of lupin acid phosphatase clearly demonstrated the homology between its two subunits. Sequenced tryptic peptides also showed 78% identity (92% similarity) to the red bean acid phosphatase. Peptides exclusive for the 50-kDa subunit are homologous to N-terminally located sequences in red bean acid phosphatase, leading to the assumption that the shorter subunit of lupin acid phosphatase is generated by the deletion of the N-terminal part of the longer subunit. Carbohydrate moiety was found to be identical in both subunits. Oligosaccharide chains released by hydrazinolysis from the both subunits were fluorescently labeled and separated by HPLC. The structure of oligosaccharides was elucidated by exoglycosidase sequencing. Seventeen percent of isolated glycans were found to be of the high-mannose type, while the rest belonged to plant complex-type structures. Most of the complex glycans were fucosylated and xylosylated; some were fucosylated or xylosylated only.

Inhibition of eukaryote protein kinases and of a cyclic nucleotide-binding phosphatase by prenylated xanthones

A series of prenylated xanthones are variously potent inhibitors of the catalytic subunit (cAK) of rat liver cyclic AMP-dependent protein kinase (PKA), rat brain Ca2+ and phospholipid-dependent protein kinase C (PKC), chicken gizzard myosin light chain kinase (MLCK), wheat embryo Ca2+-dependent protein kinase (CDPK) and potato tuber cyclic nucleotide-binding phosphatase (Pase). The prenylated xanthones examined are mostly derivatives of alpha-mangostin in which the 3-hydroxyl and 6-hydroxyl are variously substituted with groups R or R', respectively, or derivatives of 3-isomangostin (mangostanol) in which the 9-hydroxyl is substituted with groups R' or the prenyl side chain is modified. The most potent inhibitors of cAK have non-protonatable and relatively small R' and R groups. Conversely, the most potent inhibitors of PKC and MLCK have bulkier and basic R' groups. Some prenylated xanthones are also potent inhibitors of CDPK. PKC and cAK are competitively inhibited by particular prenylated xanthones whereas the compounds that are the most potent inhibitors of MLCK and CDPK are non-competitive inhibitors. Prenylated xanthones having relatively small and non-protonatable R' and R groups inhibit a high-affinity cyclic nucleotide binding Pase in a non-competitive fashion.

Inhibition of cyclic AMP-dependent protein kinase by curcumin

Curcumin [diferuloylmethane; 1,7-bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione], a major bioactive secondary metabolite found in the rhizomes of turmeric (Curcuma longa), is an inhibitor of Ca(2+)- and phospholipid-dependent protein kinase C (PKC) and of the catalytic subunit (cAK) of cyclic AMP-dependent protein kinase (IC50 values 15 and 4.8 microM, respectively). Curcumin inhibits plant Ca(2+)-dependent protein kinase (CDPK) (IC50 41 microM), but does not inhibit myosin light chain kinase or a high affinity 3',5'-cyclic AMP-binding phosphatase. Curcumin inhibits cAK, PKC and CDPK in a fashion that is competitive with respect to both ATP and the synthetic peptide substrate employed. The IC50 values for inhibition of cAK by curcumin are very similar when measured with kemptide (LRRASLG) (in the presence or absence of ovalbumin) or with casein or histone III-S as substrates. However, the presence of bovine serum albumin (0.8 mg ml-1) largely overcomes inhibition of cAK by curcumin.