Poly(ADP-ribose) polymerase-1 : domain C structure, poly(ADP-ribosyl)ation sites and physiological functions
Poly(ADP-ribose) polymerase-1 (PARP-1) is an abundant nuclear protein that catalyzes the cleavage of NAD⁺ into nicotinamide and ADP-ribose moiety, the latter of which may be covalently attached as a branched polymer of poly(ADP-ribose) to PARP-1 itself (automodification) or to other nuclear acceptor proteins (transmodification). PARP-1 plays pivotal roles in many fundamental biological processes, including DNA repair, gene expression, cell death and cell cycle regulation. The multiple functions of PARP-1 in various cellular events correlate well to its roles in carcinogenesis, inflammatory response, neural function, and aging. PARP-1 has a modular organization comprising six independent domains (domain A-F). Each domain has its own characteristic function in PARP-1 enzymatic catalysis. In this dissertation, the solution structure of domain C was determined by multi-dimensional NMR spectroscopy. To complement the structural results, the requirement of domain C for PARP-1 catalysis was demonstrated using activity assays. This structure-function relationship study will help to unveil the mechanism of the PARP-1 reaction, and should provide valuable information for the design of more potent and selective PARP-1 inhibitors. The determination of poly(ADP-ribosyl)ation sites is critical for understanding the biological roles of this modification. However, the identification of poly(ADPribosyl)ation sites has countered some daunting technical limitations due to the difficulties resulting from the heterogenous nature of this modification. In this dissertation, a methodology based on mass spectrometry is developed and used to identify ADP-ribosylation sites within the automodification domain (domain D) of PARP-1. Using this method, we were able to unambiguously localize three ADPribosylation sites on domain D. This method can be readily applied to study the transmodification of other substrates as well as PARP-1 automodification. As many as seventeen PARP homologues exist in the human proteome. The functional redundancy of the multiple PARP proteins has complicated the analysis of mammalian PARP-1 function in vivo. We have probed the biological roles of PARP-1 using an artificial PARP-1 pathway in yeast, an organism lacking the endogenous PARP-1. Our data suggest the heterologously expressed human PARP-1 in yeast retains some similar functions as it does in mammalian cells. Furthermore, a new function of PARP-1 in ribosome biogenesis was proposed.