Identification and characterization of a human mitochondrial NAD kinase.
Nature communications
confidence
Key findings
C5orf33 identified as human mitochondrial NAD kinase; likely source of mitochondrial NADP(+); no clinical/biological endpoints reported.
View source on PubMed (PMID 23212377) ↗
- Sample size
- Not reported
- Population
- Human HEK293A cells and human tissues (in vitro and tissue expression analysis)
- Dosing
- Not reported
- Duration
- Not reported
- Route
- Not reported
- Blinding
- not_reported
- Controls
- none
- Drug class
- coenzyme
Full abstract
NAD kinase is the sole NADP(+) biosynthetic enzyme. Despite the great significance of NADP(+), to date no mitochondrial NAD kinase has been identified in human, and the source of human mitochondrial NADP(+) remains elusive. Here we present evidence demonstrating that a human protein of unknown function, C5orf33, is a human mitochondrial NAD kinase; this protein likely represents the missing source of human mitochondrial NADP(+). The C5orf33 protein exhibits NAD kinase activity, utilizing ATP or inorganic polyphosphate, and is localized in the mitochondria of human HEK293A cells. C5orf33 mRNA is more abundant than human cytosolic NAD kinase mRNA in almost all tissues examined. We further show by database searches that some animals and protists carry C5orf33 homologues as their sole NADP(+) biosynthetic enzyme, whereas plants and fungi possess no C5orf33 homologue. These observations provide insights into eukaryotic NADP(+) biosynthesis, which has pivotal roles in cells and organelles.