Abstract
Adenosylhomocysteinase (AHCY) is a unique enzyme and one of the most conserved proteins in living organisms. AHCY catalyzes the reversible break of S-adenosylhomocysteine (SAH), the by-product and a potent inhibitor of methyltransferases activity. In mammals, AHCY is the only enzyme capable of performing this reaction. Controlled subcellular localization of AHCY is believed to facilitate local transmethylation reactions, by removing excess of SAH. Accordingly, AHCY is recruited to chromatin during replication and active transcription, correlating with increasing demands for DNA, RNA, and histone methylation. AHCY deletion is embryonic lethal in many organisms (from plants to mammals). In humans, AHCY deficiency is associated with an incurable rare recessive disorder in methionine metabolism. In this review, we focus on the AHCY protein from an evolutionary, biochemical, and functional point of view, and we discuss the most recent, relevant, and controversial contributions to the study of this enzyme.
Highlights
The metabolic enzyme adenosylhomocysteinase (AHCY; alternatively called SAHH for S-adenosyl-L-homocysteine hydrolase, according to HUGO Gene Nomenclature Committee) is one of the most conserved enzymes in living organisms, including bacteria, nematodes, yeast, plants, insects, and vertebrates (Kusakabe et al, 2015)
As SAM and SAH compete for the SAM-binding pocket of MTases, the SAM:SAH ratio is considered an indicator of the methylation capacity of cells, and its decrease can correlate with a reduction of the methylation potential (Clarke, 2001; Petrossian and Clarke, 2011)
While some methyltransferases retain most of their activity at different SAM:SAH ratios, such as the glycine N-methyltransferase, others are more susceptible to SAH elevation, including tRNA or arginine methyltransferases (Clarke, 2001; Richon et al, 2011; Zhang and Zheng, 2016)
Summary
The metabolic enzyme adenosylhomocysteinase (AHCY; alternatively called SAHH for S-adenosyl-L-homocysteine hydrolase, according to HUGO Gene Nomenclature Committee) is one of the most conserved enzymes in living organisms, including bacteria, nematodes, yeast, plants, insects, and vertebrates (Kusakabe et al, 2015). The potential impact of AHCY in controlling methylation of DNA, RNA, and histones has been studied in many model organisms and cell types.
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