Abstract
Catalytically active proteins with divergent dual functions are often described as ‘moonlighting’. In this work we characterize a new, chromatin-based function of Lys20, a moonlighting protein that is well known for its role in metabolism. Lys20 was initially described as homocitrate synthase (HCS), the first enzyme in the lysine biosynthetic pathway in yeast. Its nuclear localization led to the discovery of a key role for Lys20 in DNA damage repair through its interaction with the MYST family histone acetyltransferase Esa1. Overexpression of Lys20 promotes suppression of DNA damage sensitivity of esa1 mutants. In this work, by taking advantage of LYS20 mutants that are active in repair but not in lysine biosynthesis, the mechanism of suppression of esa1 was characterized. First we analyzed the chromatin landscape of esa1 cells, finding impaired histone acetylation and eviction. Lys20 was recruited to sites of DNA damage, and its overexpression promoted enhanced recruitment of the INO80 remodeling complex to restore normal histone eviction at the damage sites. This study improves understanding of the evolutionary, structural and biological relevance of independent activities in a moonlighting protein and links metabolism to DNA damage repair.
Highlights
The characterization of a gene or protein generally focuses on the context in which it first appeared; distinct functions of proteins are often unsuspected
Lys20 was defined as a moonlighting protein because the lys20-E155A mutant was catalytically inactive as homocitrate synthases (HCS), it still suppressed the DNA damage sensitivity of esa1 [26]
We found that upon DNA damage induction, more Lys20 bound to chromatin compared to non-induced conditions
Summary
The characterization of a gene or protein generally focuses on the context in which it first appeared; distinct functions of proteins are often unsuspected. Dual or moonlighting functions for a single protein have central implications in the evolution of complex processes and can provide insight into regulatory mechanisms that connect cellular pathways and functions [1]. Lys and its isozyme Lys are defined as homocitrate synthases (HCS). These enzymes catalyze the first committed and rate-limiting step of the ␣-aminoadipate lysine biosynthesis pathway of fungi [8]. Cell biological and refined biochemical studies revealed that Lys has a predominant nuclear localization [11,12]. Despite these reports, a distinct nuclear role of Lys remained speculative for many years
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