Date of Award

Summer 7-28-2012

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

First Advisor

George Yujun Zheng

Abstract

Protein arginine methyltransferase 1 (PRMT1) is a key posttranslational modification enzyme that catalyzes the methylation of specific arginine residues in histone and nonhistone protein substrates, regulating diverse cellular processes such as transcriptional initiation, RNA splicing, DNA repair, and signal transduction. Recently the essential roles of PRMT1 in cancer and cardiovascular complications have intrigued much attention. Developing effective PRMT inhibitors therefore is of significant therapeutic value. The research on PRMT inhibitor development however is greatly hindered by poor understanding of the biochemical basis of protein arginine methylation and lack of effective assays for PRMT1 inhibitor screening.

Herein, we report our effort in the kinetic mechanism study as well as the fluorescent probe and inhibitor development for PRMT1. New fluorescent reporters were designed and applied to perform single-step analysis of substrate binding and methylation of PRMT1. Using these reporters, we performed transient-state fluorescence measurements to dissect the rate constants along the PRMT1 catalytic coordinate. The data give evidence that the chemistry of methyl transfer is the major rate-limiting step, and that binding of the cofactor SAM or SAH affects the association and dissociation of H4 with PRMT1. Importantly, we identified a critical kinetic step suggesting a precatalytic conformational transition induced by substrate binding. On the other hand, we discovered a type of naphthyl-sulfo (NS) compounds that block PRMT1- mediated arginine methylation at micromolar potency through a unique mechanism: they directly target the substrates but not PRMT enzymes for the observed inhibition. We also found that suramin, an anti-parasite and anti-cancer drug bearing similar functional groups, effectively inhibited PRMT1 mediated methylation. These findings about novel PRMT inhibitors and their unique inhibition mechanism provide a new way for chemical regulation of protein arginine methylation. Addionally, to dissect the interplaying relationship between different histone modification marks, we investigated how individual lysine acetylations and their different combinations at the H4 tail affect Arg-3 methylation in cis. Our data reveal that the effect of lysine acetylation on arginine methylation depends on the site of acetylation and the type of methylation. While certain acetylations present a repressive impact on PRMT-1 mediated methylation (type I methylation), lysine acetylation generally is correlated with enhanced methylation by PRMT5 (type II dimethylation). In particular, Lys-5 acetylation decreases activity of PRMT1 but increases that of PRMT5. Furthermore, hyperacetylation increases the content of ordered secondary structures of H4 tail. These findings provide new insights into the regulatory mechanism of Arg-3 methylation by H4 acetylation, and unravel that complex intercommunications exist between different posttranslational marks in cis.

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