Biochemical Assay Development for Histone Methyltransferases Using a Transcreener-Based Assay for S-Adenosylhomocysteine.

Abstract

Epigenetic regulation has been implicated in diverse diseases including cancer, diabetes, and inflammation, and high-throughput screening for histone methyltransferase (HMT) inhibitors is an area of intense drug discovery effort. HMTs catalyze the transfer of methyl group from S-adenosylmethionine (SAM) to lysine or arginine on histone tails forming the methylated products and S-adenosylhomocysteine (SAH). HMTs are challenging to incorporate into biochemical assays for a number of reasons. They have slow turnovers and low Km values for SAM, which leads to low levels of product formation, and thus requires very sensitive detection methods and/or high levels of enzyme. They also have diverse acceptor substrate requirements, ranging from peptides to intact nucleosomes. Additionally, some HMTs function as complexes of three or more proteins. Developing assays for individual HMTs, including sourcing and acquiring high quality enzymes and acceptor substrates, therefore can be laborious and expensive. We recently developed the Transcreener(®) EPIGEN Methyltransferase assay, a sensitive SAH detection method with a fluorescence polarization readout, to enable universal HMT detection independent of acceptor substrate. To facilitate screening and profiling of HMTs, we describe the development of turnkey assay systems for thirteen HMTs including identification of optimal acceptor substrates and their concentrations, optimization of detection reagents, determination of initial velocity enzyme concentrations, and measurement of inhibitor potencies.