Poly(ADP-ribose) polymerases, PARPs, transfer ADP-ribose onto target proteins from nicotinamide adenine dinucleotide (NAD + ). Current mass spectrometric analytical methods require proteolysis of target proteins, limiting the study of dynamic ADP-ribosylation on contiguous proteins. Herein, we present a matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) method that facilitates multisite analysis of ADP-ribosylation. We observe divergent ADP-ribosylation dynamics for the catalytic domains of PARPs 14 and 15, with PARP15 modifying more sites on itself (+3–4 ADP-ribose) than the closely related PARP14 protein (+1–2 ADP-ribose)—despite similar numbers of potential modification sites. We identify, for the first time, a minimal peptide fragment (18 amino-acids) that is preferentially modified by PARP14. Finally, we demonstrate through mutagenesis and chemical treatment with hydroxylamine that PARPs 14/15 prefer acidic residues. Our results highlight the utility of MALDI-TOF in the analysis of PARP target modifications and in elucidating the biochemical mechanism governing PARP target selection.

A Schwann cell can form only one internode of myelin around an axon. However, we observed the formation by a single Schwann cell of myelin around two axons of different diameters in the sural nerve of a 45-year-old man with mononeuritis multiplex. Schwann cell processes spiraled in the same direction around each axon, forming mesaxons. The findings in this case appear to be an undescribed type of aberrant myelination.

Poly (ADP‐ribose) polymerases, PARPs, are a family of 17 enzymes (in humans) that catalyze the transfer of ADP‐ribose onto target proteins from nicotinamide adenine dinucleotide (NAD+). ADP‐ribosylation occurs in a highly conserved PARP catalytic domain found in all seventeen PARPs. Significant effort using modern proteomic methods has led to the identification of thousands of potential PARP targets in the cell. Unfortunately, this analysis has not yet uncovered which sites are preferentially targeted in vivo nor the determinants for PARP family‐member specific targeting. Further, current analytical methods require proteolysis of the target protein, limiting the study of dynamic ADP‐ribosylation. Herein, we present a matrix‐assisted laser desorption/ionization time of flight (MALDI‐ TOF) method using thin‐layer chromatography (TLC) that facilitates population‐wide analysis of ADP‐ribosylation. Using this method, we observe divergent ADP‐ribosylation dynamics for PARPs 14 and 15, with PARP15 modifying more sites on itself (+4–5 ADP‐ribose) than the closely related PARP14 protein (+1–2 ADP‐ribose) ‐ despite similar numbers of potential modification sites. Using this method, we also identify, for the first time, a minimal peptide fragment (18 amino‐acids) that is preferentially modified by PARP14. We have identified the specific glutamate (E) residue that is targeted on this peptide, and we demonstrate through mutagenesis and chemical treatment with hydroxylamine that PARP14 prefers acidic residues. The development of this technique will not only be useful in identifying the basic biochemistry governing ADP‐ribosylation but should find utility in the identification of PARP family‐member specific peptide targets and inhibitors.