Histone Acetyltransferases

Abstract

As an important posttranslational modification, protein acetylation plays critical roles in many biological processes such as gene transcription, DNA damage repair, apoptosis and metabolism. The acetylation occurs on the ε-amino group of specific lysine residues, and is catalyzed by histone acetyltransferases (HATs). In cellular contexts, HATs are found to target hundreds and thousands of substrates including histone and nonhistone proteins. Lysine acetylation changes the microenvironment of protein and may potentially alter protein activity and protein-protein interaction. The goal of this dissertation project is to investigate the impact of lysine acetylation on the catalysis of MYST HATs, and to establish the strategy for labeling substrates of the MYST HATs at cellular level. To understand the regulatory mechanism of MYST HATs, a detailed study was carried out to investigate the active site lysine acetylation of two MYST HATs (MOF and Tip60). Autoradiography and immunoblotting data shows that mutation of active site lysine differentially affects the enzyme autoacetylation activity and the cognate substrate acetylation activity. In addition, deacetylated MOF and Tip60 were prepared by using the nonspecific lysine deacetylase Sirt1. Kinetic study demonstrated that the acetylation of the active site lysine on MYST HATs marginally modulates the HAT catalysis. This work provides new insights into the regulatory mechanism of MYST catalysis. In the second part of my work, we designed and synthesized a series of Ac-CoA analogs conjugated with alkynyl or azido functional groups. Meanwhile, the active site of the MOF was engineered to expand the cofactor binding capability. Fluorescence screening was carried out to characterize the enzyme activity to Ac-CoA analogs. MOF-I317A with all analogs and MOF-I317A/H273A-5HYCoA were identified and further applied in the labeling of the cognate histone H4 protein and HAT substrates in 293T cell lysate. Visualizing of the labeled substrate was achieved using the alkynyl or azido-tagged fluorescent reporters through the copper-catalyzed azide−alkyne cycloaddi on.As expected, the histone H4 protein was successfully labeled by the active enzyme-cofactor pairs. More intriguingly, multiple protein bands in cell lysate were labeled and observed. This work provides a new versatile strategy in exploring the substrates of MYST HATs at the proteomic level.