In vitro hydrogen production by mammal [FeFe]-hydrogenase-like protein

Although emerging evidence in mammals reveals that exogenously applied H₂ positively regulates numerous physiological and pathological responses, it remains unclear whether and how mammalian cells produce H₂ endogenously. Here, we report for the first time that recombinant human (Homo sapiens) and pig (Sus scrofa) nuclear prelamin recognition factor (Narf)-like proteins (also known as H. sapiens iron-only hydrogenase-like protein 1 [HsIOP1] and S. scrofa cytosolic iron-sulfur assembly component 3 [SsCIAO3], belonging to the [FeFe]-hydrogenase-like protein family), when expressed in a prokaryotic system, can potentially catalyze H₂ production in vitro. Anaerobic induction was clearly observed. Further investigation of the transcriptome database revealed the widespread presence of these proteins in human and pig tissues. Sequence and structural analyses revealed that both HsIOP1 and SsCIAO3 may contain four conserved cysteine residues, forming a [4Fe4S] cluster, similar to the known [FeFe]-hydrogenase in Chlamydomonas reinhardtii. According to the observed hydrogenase activities of HsIOP1 and SsCIAO3 produced in Escherichia coli and the ubiquitous presence of Narf-like proteins in eukaryotic organisms, we propose that H₂ production may be a universal phenomenon in eukaryotic organisms. Based on the results of the evolutionary tree, it was further hypothesized that hydrogen metabolism may have been ignored in the evolution and development of eukaryotic cells for a considerable time.