Histone substrate

Binding of Histone Substrates by HATs of the GNAT Family... 

Traditionally, HAT activity is measured with a discontinuous radioactive filterbinding assay, which uses pH]acetyl-CoA as a histone acetyltransferase substrate [46]. The transfer of [ H]acetyl-groups to the histone substrate by histone acetyltransferases is detected by liquid scintillation counting of pHjacetylated histones, which are retained on a phosphocellulose disk. Due to its discontinuous character, this assay is technically problematic and not ideal for kinetic analysis. Hence, other assays that work with radiolabeled acetyl-CoA have been described that are suitable for a higher throughput. These work with streptavidin-covered beads [47] or a variant of the SPA with microtiter plates that contain a scintillant (FlashPlates) [48]. But as all these protocols are based on radioactively labeled substrates, they apparently show the same disadvantages that were described for the radioactive HDAC assay protocols. Therefore, nonradioactive assays have been developed to study histone acetyltransferase activity. 

Another antibody-based immunosorbent assay that can be used to determine HAT activity uses a secondary anti-IgG antibody, which is directed against the primary antibody and is labeled with the lanthanide Europium (Eu). After another washing step that removes all nonbound secondary antibody, one last incubation step is performed, which releases the lanthanide ion from the antibody, so that the final detection of time-resolved fluorescence (340/615 nm) caused by the released metal ion correlates with the acetylation level of the oligepeptide histone substrate, which is correlated with enzymatic activity. So far. 

P RMTs lead to the methylation of certain arginine residues in histones as depicted in Table 12.1. They are not restricted to histone substrates but also catalyze the methylation of other proteins that play a role in signal transduction and cell proliferation [15]. Usually glycine-alanine-arginine patches (called GAR motifs)... 

Protein lysine methyltransferases (PKMTs) are a family of enzymes that transfer the activated methyl group from S-adenosyl-L-methionine (SAM) to specific lysine residues on various substrates. The PKMTs have been causally linked to various human diseases including cancer [140], Huntington s disease [141], and growth defects [142, 143]. The substrates of the PKMTs are typically histones [144-146], but there are several methyltransferases methylate non-histone substrates, such as the tumor suppressor p53 [147, 148], the estrogen receptor ERa [149], and the ATPase Reptin [150]. Given the importance of these enzymes in normal and... 

Figure 5.13 Histone demethylases. Structures and mechanisms are illustrated for the two subclasses of histone lysine demethylases. (a) Views from an X-ray crystal structure of LSDl (PDB ID 2V1D) in complex with cofactor FAD and a peptide substrate analogue, where methionine replaces methylated lysine, and outline mechanism of the LSDl-catalysed demethylation reaction, (b) Views from an X-ray crystal structure of JMJD2A (PDB ID 20Q6) in complex with co-factor analogue N-oxa-lylglycine and histone substrate trimethylated at H3K9 (note that Ni(II) replaces Fe(II) for crystallography), and outline mechanism of JmjC-domain catalysed lysine demethylation. (c) Representative inhibitors of LSDl and JmjC-domain demethylases.

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