Molecular Mechanisms, Pathways and Inhibition of Acetyl-Transfer Reactions

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The acetylation of proteins and RNA, and acetyl-transfer reactions that produce cellular metabolites, are evolutionarily conserved modifications that are essential for life. The post- or co-translational acetylation of proteins provides an essential mechanism for organisms to react to external and internal stimuli; examples include acetylation of the e-amino group of lysine side chains of histone proteins by histone acetyltransferases (HATs) or the N-terminal a-amino group by N-terminal acetyltransferases (NATs), respectively; and the acetylation at the N4 position of cytidine bases by Nat10. Acetyl-transfer reactions produce cellular metabolites that can mediate the biosynthesis of essential cellular building blocks; examples include: acetyl-CoA produced by ATP-citrate lyase (ACLY) and acetyl-CoA synthetase short- chain family member 2 (ACSS2); fatty acids produced by Fatty Acid Synthase (FASN); and cholesterol and isoprenoids formed through the sequential reactions of many enzymes. The enzymes that mediate acetyl- transfer reactions often function in the context of multiple domain proteins or multisubunit protein complexes, which play essential roles in the regulation of cognate substrate recognition and targeting and/or catalytic fidelity. How the various protein domains and protein cofactors cooperate for their respective acetyl-transfer reactions remains poorly understood. Correlating with their biological importance, the aberrant activities of acetyl-transfer enzymes or their regulatory proteins have been associated with several maladies including cancers, rare genetic disorders, cardiovascular diseases and metabolic and neurodegenerative syndromes, thus making these enzymes attractive drug targets for therapy. Taken together, acetyl-transfer reactions play an important regulatory function in the vast majority of the human proteome, RNAome and metabolome, and aberrant acetyl-transfer reaction function is correlated with human disease. Despite the importance of acetyl-transfer reactions, mechanistic information regarding their distinct modes of regulation are poorly understood and pharmacological agents that target them are not available. In this proposal, we will address the following broad questions underlying acetyl-transfer reactions: (A) How do protein and RNA acetyltransferases mediate substrate specificity? (B) How do auxiliary proteins and ribosome association contribute to NAT function? (C) How does acetyl-CoA metabolism link to chromatin regulation and fatty acid synthesis? (D) Can we leverage mechanistic and structural information to develop potent and selective inhibitors for acetyl-transfer reactions? Together, these studies will reveal how a common acetyltransferase fold is modulated by other proteins or domains to mediate the acetylation of distinct substrates, how N-terminal protein acetylation is modulated by regulatory and associated factors, dissect the molecular mechanism of essential acetyl-transfer enzymes, and provide probes to better understand the biology of acetyl-transfer enzymes with clear implications for therapy.