3 years ago

A Functional Link Between NAD+ Homeostasis and N-terminal Protein Acetylation in Saccharomyces cerevisiae.

Su-Ju Lin, Michelle Salemi, Trevor Croft, Christol James Theoga Raj, Brett S Phinney
Nicotinamide adenine dinucleotide (NAD+) is an essential metabolite participating in cellular redox chemistry and signaling, and the complex regulation of NAD+ metabolism is not yet fully understood. To investigate this, we established a NAD+-intermediate specific reporter system to identify factors required for salvage of metabolically-linked nicotinamide (NAM) and nicotinic acid (NA). Mutants lacking components of the NatB complex, NAT3 and MDM20, appeared as hits in this screen. NatB is an Nα-terminal-acetyltransferase responsible for acetylation of the amino terminus of specific Met-retained peptides. In NatB mutants, increased NA/NAM levels were concomitant with decreased NAD+ We identified the vacuolar pool of nicotinamide riboside (NR) as the source of this increased NA/NAM. This NR pool is increased by nitrogen starvation, suggesting NAD+ and related metabolites may be trafficked to vacuole for recycling. Supporting this, increased NA/NAM release in NatB mutants was abolished by deleting the autophagy protein ATG14 We next examined Tpm1 (tropomyosin) whose function is regulated by NatB mediated acetylation, and Tpm1 overexpression (TPM1-oe) was shown to restore some NatB mutant defects. Interestingly, although TPM1-oe largely suppressed NA/NAM release in NatB mutants, it did not restore NAD+ levels. We showed that decreased nicotinamide mononucleotide adenylyltransferases (Nma1/Nma2) levels likely caused the NAD+ defects, and NMA1-oe was sufficient to restore NAD+ NatB mediated N-terminal acetylation of Nma1 and Nma2 appears essential for maintaining NAD+ levels. In summary, our results support a connection between NatB mediated protein acetylation and NAD+ homeostasis. Our findings may contribute to understanding the molecular basis and regulation of NAD+ metabolism.

Publisher URL: http://doi.org/10.1074/jbc.M117.807214

DOI: 10.1074/jbc.M117.807214

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