Expression in E. coli of the catalytic domain of rat poly(ADP-ribose)polymerase

Quantitative site-specific ADP-ribosylation profiling of DNA-dependent PARPs

An important feature of poly(ADP-ribose) polymerases (PARPs) is their ability to readily undergo automodification upon activation. Although a growing number of substrates were found to be poly(ADP-ribosyl)ated, including histones and several DNA damage response factors, PARPs themselves are still considered as the main acceptors of poly(ADP-ribose). By monitoring spectral counts of specific hydroxamic acid signatures generated after the conversion of the ADP-ribose modification onto peptides by hydroxylamine hydrolysis, we undertook a thorough mass spectrometry mapping of the glutamate and aspartate ADP-ribosylation sites onto automodified PARP-1, PARP-2 and PARP-3. Thousands of hydroxamic acid-conjugated peptides were identified with high confidence and ranked based on their spectral count. This semi-quantitative approach allowed us to locate the preferentially targeted residues in DNA-dependent PARPs. In contrast to what has been reported in the literature, automodification of PARP-1 is not predominantly targeted towards its BRCT domain. Our results show that interdomain linker regions that connect the BRCT to the WGR module and the WGR to the PRD domain undergo prominent ADP-ribosylation during PARP-1 automodification. We also found that PARP-1 efficiently automodifies the D-loop structure within its own catalytic fold. Interestingly, additional major ADP-ribosylation sites were identified in functional domains of PARP-1, including all three zinc fingers. Similar to PARP-1, specific residues located within the catalytic sites of PARP-2 and PARP-3 are major targets of automodification following their DNA-dependent activation. Together our results suggest that poly(ADP-ribosyl)ation hot spots make a dominant contribution to the overall automodification process.

Characterization of the necrotic cleavage of poly(ADP-ribose) polymerase (PARP-1): implication of lysosomal proteases

The poly(ADP-ribose) polymerase (PARP-1), a 113 kDa nuclear enzyme, is cleaved in fragments of 89 and 24 kDa during apoptosis. This cleavage has become a useful hallmark of apoptosis and has been shown to be done by DEVD-ase caspases, a family of proteases activated during apoptosis. Interestingly, PARP-1 is also processed during necrosis but a major fragment of 50 kDa is observed. This event is not inhibited by zVAD-fmk, a broad spectrum caspase inhibitor, suggesting that these proteases are not implicated in the necrotic cleavage of PARP-1. Since lysosomes release their content into the cytosol during necrosis, the proteases liberated could produce the cleavage of PARP-1. We therefore isolated lysosomal rich-fractions from Jurkat T cells. Our results reveal that the in vitro lysosomal proteolytic cleavage of affinity purified bovine PARP-1 is composed of fragments corresponding, in apparent molecular weight and function, to those found in Jurkat T cells treated with necrotic inducers like 0.1% H2O2, 10% EtOH or 100 microM HgCl2. Moreover, we used purified lysosomal proteases (cathepsins B, D and G) in an in vitro cleavage assay and found that cathepsins B and G cleaved PARP-1 in fragments also found with the lysosomal rich-fractions. These findings suggest that the necrotic cleavage of PARP-1 is caused in part or in totality by lysosomal proteases released during necrosis.

Molecular and biochemical features of poly (ADP-ribose) metabolism

In the past five years, poly(ADP-ribosyl)ation has developed greatly with the help of molecular biology and the improvement of biochemical techniques. In this article, we describe the physico-chemical properties of the enzymes responsible for the synthesis and degradation of poly(ADP-ribose), respectively poly(ADP-ribose) polymerase and poly(ADP-ribose) glycohydrolase. We then discuss the possible roles of this polymer in DNA repair and replication as well as in cellular differentiation and transformation. Finally, we put forward various hypotheses in order to better define the function of this polymer found only in eucaryotes.

Expression in Escherichia coli of the 36 kDa domain of poly(ADP-ribose) polymerase and investigation of its DNA binding properties

We have expressed in Escherichia coli the 36 kDa domain of the human poly(ADP-ribose) polymerase. This polypeptide comprises the C-terminal part of the DNA binding domain, as well as the automodification region of the enzyme, but lacks the zinc-finger motifs of the N-terminal region and the C-terminal catalytic domain. By probing the crude E. coli protein extracts with radioactive DNA probes (South-Western blots), we have shown that the 36 kDa domain binds a DNA probe of 222 bp but does not bind a shorter probe of 66 bp. This interaction is stronger when the polypeptide is fused to the 55 kDa catalytic domain of the enzyme.

Detection of poly(ADP ribose) polymerase in crude extracts by activity-blot

We have recently devised an activity-blot procedure permitting the detection, on the same nitrocellulose sheet, of the functional poly(ADP ribose) polymerase (PARP) activity as well as the immunostained active peptide(s) after renaturation of the transferred protein(s). Using this technique we have analyzed the PARP activity in higher and lower eukaryotes directly on crude extracts from cell cultures. This procedure has been extended also to in situ screening of bacterial colonies expressing the PARP enzymatic activity.