Search

ADP-ribosylation is a posttranslational modification that modulates the functions of many target proteins. We previously showed that the fungal toxin brefeldin A (BFA) induces the ADP-ribosylation of C-terminal-binding protein-1 short-form/BFA-ADP-ribosylation substrate (CtBP1-S/BARS), a bifunctional protein with roles in the nucleus as a transcription factor and in the cytosol as a regulator of membrane fission during intracellular trafficking and mitotic partitioning of the Golgi complex. Here, we report that ADP-ribosylation of CtBP1-S/BARS by BFA occurs via a nonconventional mechanism that comprises two steps: (i) synthesis of a BFA-ADP-ribose conjugate by the ADP-ribosyl cyclase CD38 and (ii) covalent binding of the BFA-ADP-ribose conjugate into the CtBP1-S/BARS NAD+-binding pocket. This results in the locking of CtBP1-S/BARS in a dimeric conformation, which prevents its binding to interactors known to be involved in membrane fission and, hence, in the inhibition of the fission machinery involved in mitotic Golgi partitioning. As this inhibition may lead to arrest of the cell cycle in G2, these findings provide a strategy for the design of pharmacological blockers of cell cycle in tumor cells that express high levels of CD38. [ABSTRACT FROM AUTHOR]

ADP-ribosyl cyclases are ubiquitous enzymes responsible for synthesis from NAD+ of the intracellular calcium-releasing signal molecules cyclic ADP-ribose (cADPR) and nicotinic acid adenine dinucleotide phosphate (NAADP+). Here, we show that cyclases from lower and higher Metazoa also synthesize three adenylic dinucleotides from cADPR and adenine: diadenosine diphosphate and two isomers thereof. These dinucleotides are present and metabolized in mammalian cells and affect intracellular calcium and cell proliferation. The diadenosine diphosphate isomers are naturally occurring nucleotides containing an N-glycosidic bond different from the usual Cl'-N9. The identification of these members of the family of NAD+-derived, calcium-active nucleotides opens new areas of investigation into their functional cooperation with cADPR and NAADP+ and into their involvement in the physiology and pathology of calcium-controlled cell functions. [ABSTRACT FROM AUTHOR]

During prolonged starvation, fructose 1,6bisphosphatase (EC 3.1.3.11) activity in rabbit liver and kidney shows a transient decrease during the first 36 hr, before rising at 96 hr to levels severalfold higher than those found in the livers of fed animals. Proteolytic activity appears in the 105,000 x g supernatant fraction within several hours of starvation, and continues to increase during the entire 96-hr period. On refeeding, the activities return to nearly the control levels within 24 hr. The catalytic properties of fructose 1,6-bisphosphatase isolated from the livers of fasted rabbits are similar to those of the enzyme from fed animals, but its structure is modified, since it no longer contains the single tryptophan residue located near the NH(2)-terminus in the native enzyme. Thus this tryptophan residue is not required for the neutral pH optimum. The structural changes and the transient decrease in activity may be related to the observed increase in "free" proteolytic activity.