Synthesizing and salvaging NAD: lessons learned from Chlamydomonas reinhardtii.
The essential coenzyme nicotinamide adenine dinucleotide (NAD+) plays important roles in metabolic reactions and cell regulation in all organisms. Bacteria, fungi, plants, and animals use different pathways to synthesize NAD+. Our molecular and genetic data demonstrate that in the unicellular green...
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Public Library of Science (PLoS)
2010-09-01
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| Series: | PLoS Genetics |
| Online Access: | https://journals.plos.org/plosgenetics/article/file?id=10.1371/journal.pgen.1001105&type=printable |
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| author | Huawen Lin Alan L Kwan Susan K Dutcher |
| author_facet | Huawen Lin Alan L Kwan Susan K Dutcher |
| author_sort | Huawen Lin |
| collection | DOAJ |
| description | The essential coenzyme nicotinamide adenine dinucleotide (NAD+) plays important roles in metabolic reactions and cell regulation in all organisms. Bacteria, fungi, plants, and animals use different pathways to synthesize NAD+. Our molecular and genetic data demonstrate that in the unicellular green alga Chlamydomonas NAD+ is synthesized from aspartate (de novo synthesis), as in plants, or nicotinamide, as in mammals (salvage synthesis). The de novo pathway requires five different enzymes: L-aspartate oxidase (ASO), quinolinate synthetase (QS), quinolate phosphoribosyltransferase (QPT), nicotinate/nicotinamide mononucleotide adenylyltransferase (NMNAT), and NAD+ synthetase (NS). Sequence similarity searches, gene isolation and sequencing of mutant loci indicate that mutations in each enzyme result in a nicotinamide-requiring mutant phenotype in the previously isolated nic mutants. We rescued the mutant phenotype by the introduction of BAC DNA (nic2-1 and nic13-1) or plasmids with cloned genes (nic1-1 and nic15-1) into the mutants. NMNAT, which is also in the de novo pathway, and nicotinamide phosphoribosyltransferase (NAMPT) constitute the nicotinamide-dependent salvage pathway. A mutation in NAMPT (npt1-1) has no obvious growth defect and is not nicotinamide-dependent. However, double mutant strains with the npt1-1 mutation and any of the nic mutations are inviable. When the de novo pathway is inactive, the salvage pathway is essential to Chlamydomonas for the synthesis of NAD+. A homolog of the human SIRT6-like gene, SRT2, is upregulated in the NS mutant, which shows a longer vegetative life span than wild-type cells. Our results suggest that Chlamydomonas is an excellent model system to study NAD+ metabolism and cell longevity. |
| format | Article |
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| issn | 1553-7390 1553-7404 |
| language | English |
| publishDate | 2010-09-01 |
| publisher | Public Library of Science (PLoS) |
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| series | PLoS Genetics |
| spelling | doaj-art-53c82afa1452483aa668d73d698439a82025-08-20T02:31:50ZengPublic Library of Science (PLoS)PLoS Genetics1553-73901553-74042010-09-0169e100110510.1371/journal.pgen.1001105Synthesizing and salvaging NAD: lessons learned from Chlamydomonas reinhardtii.Huawen LinAlan L KwanSusan K DutcherThe essential coenzyme nicotinamide adenine dinucleotide (NAD+) plays important roles in metabolic reactions and cell regulation in all organisms. Bacteria, fungi, plants, and animals use different pathways to synthesize NAD+. Our molecular and genetic data demonstrate that in the unicellular green alga Chlamydomonas NAD+ is synthesized from aspartate (de novo synthesis), as in plants, or nicotinamide, as in mammals (salvage synthesis). The de novo pathway requires five different enzymes: L-aspartate oxidase (ASO), quinolinate synthetase (QS), quinolate phosphoribosyltransferase (QPT), nicotinate/nicotinamide mononucleotide adenylyltransferase (NMNAT), and NAD+ synthetase (NS). Sequence similarity searches, gene isolation and sequencing of mutant loci indicate that mutations in each enzyme result in a nicotinamide-requiring mutant phenotype in the previously isolated nic mutants. We rescued the mutant phenotype by the introduction of BAC DNA (nic2-1 and nic13-1) or plasmids with cloned genes (nic1-1 and nic15-1) into the mutants. NMNAT, which is also in the de novo pathway, and nicotinamide phosphoribosyltransferase (NAMPT) constitute the nicotinamide-dependent salvage pathway. A mutation in NAMPT (npt1-1) has no obvious growth defect and is not nicotinamide-dependent. However, double mutant strains with the npt1-1 mutation and any of the nic mutations are inviable. When the de novo pathway is inactive, the salvage pathway is essential to Chlamydomonas for the synthesis of NAD+. A homolog of the human SIRT6-like gene, SRT2, is upregulated in the NS mutant, which shows a longer vegetative life span than wild-type cells. Our results suggest that Chlamydomonas is an excellent model system to study NAD+ metabolism and cell longevity.https://journals.plos.org/plosgenetics/article/file?id=10.1371/journal.pgen.1001105&type=printable |
| spellingShingle | Huawen Lin Alan L Kwan Susan K Dutcher Synthesizing and salvaging NAD: lessons learned from Chlamydomonas reinhardtii. PLoS Genetics |
| title | Synthesizing and salvaging NAD: lessons learned from Chlamydomonas reinhardtii. |
| title_full | Synthesizing and salvaging NAD: lessons learned from Chlamydomonas reinhardtii. |
| title_fullStr | Synthesizing and salvaging NAD: lessons learned from Chlamydomonas reinhardtii. |
| title_full_unstemmed | Synthesizing and salvaging NAD: lessons learned from Chlamydomonas reinhardtii. |
| title_short | Synthesizing and salvaging NAD: lessons learned from Chlamydomonas reinhardtii. |
| title_sort | synthesizing and salvaging nad lessons learned from chlamydomonas reinhardtii |
| url | https://journals.plos.org/plosgenetics/article/file?id=10.1371/journal.pgen.1001105&type=printable |
| work_keys_str_mv | AT huawenlin synthesizingandsalvagingnadlessonslearnedfromchlamydomonasreinhardtii AT alanlkwan synthesizingandsalvagingnadlessonslearnedfromchlamydomonasreinhardtii AT susankdutcher synthesizingandsalvagingnadlessonslearnedfromchlamydomonasreinhardtii |