Fig. 7: Mechanistic model of PARP1-dependent PARylation derived by time-resolved ATR-FTIR spectroscopy.

Directly after NAD⁺ addition binding of NAD⁺ to the catalytic centre induces distinct structural changes of PARP1. This is followed by the release of PARP1 from DNA, which is reflected by a decrease of PARP1 signal intensity (amide I (1645 cm⁻¹) and amide II (1548 cm⁻¹) bands), and the simultaneous formation of PAR, which is reflected by an increase of PAR signal intensities [anti-symmetric (1236 cm⁻¹) and symmetric (1074 cm⁻¹) phosphate vibrations]. The observed formation of PAR is mainly due to trans-PARylation of streptavidin, which is mediated by the close proximity of streptavidin to the DNA strand break.