Human mitochondrial pyrophosphatase: cDNA cloning and analysis of the gene in patients with mtDNA depletion syndromes

Abstract

Pyrophosphatases (PPases) catalyze the hydrolysis of inorganic pyrophosphate generated in several cellular enzymatic reactions. A novel human pyrophosphatase cDNA encoding a 334-amino-acid protein approximately 60% identical to the previously identified human cytosolic PPase was cloned and characterized. The novel enzyme, named PPase-2, was enzymatically active and catalyzed hydrolysis of pyrophosphate at a rate similar to that of the previously identified PPase-1. A functional mitochondrial import signal sequence was identified in the N-terminus of PPase-2, which targeted the enzyme to the mitochondrial matrix. The human pyrophosphatase 2 gene (PPase-2) was mapped to chromosome 4q25 and the 1.4-kb mRNA was ubiquitously expressed in human tissues, with highest levels in muscle, liver, and kidney. The yeast homologue of the mitochondrial PPase-2 is required for mitochondrial DNA maintenance and yeast cells lacking the enzyme exhibit mitochondrial DNA depletion. We sequenced the PPA2 gene in 13 patients with mitochondrial DNA depletion syndromes (MDS) of unknown cause to determine if mutations in the PPA2 gene of these patients were associated with this disease. No pathogenic mutations were identified in the PPA2 gene of these patients and we found no evidence that PPA2 gene mutations are a common cause of MDS in humans.

Alterations in Energy Metabolism, Neuroprotection and Visual Signal Transduction in the Retina of Parkinsonian, MPTP-Treated Monkeys

“…Taken together, these data underscore that MPTP-induced mitochondrial complex I dysfunction can lead to alterations in the levels of other components of the respiratory chain, in analogy to what occurs in PD [6,75,80] and other neurodegenerative diseases affecting the brain and/or the retina. In a related fashion, an additional enzyme whose levels we have found decreased in the parkinsonian monkey retina is inorganic pyrophosphatase 1 (PPA1), which is responsible for modulating Pi levels and is intimately linked to cell survival [81,82]. Given that its activity is coupled to reactions in which PPi is released, and that it provides a thermodynamic pull for many biosynthetic reactions, its lower levels found in our experimental system are consistent with a situation in which the production of ATP is decreased due to the MPTP-provoked mitochondrial dysfunction.…”

Proteome map of Aspergillus nidulans during osmoadaptation

“…Similarly, XP_660572.1 (spot 1180; homologous to A. fumigatus Af293 inorganic diphosphatase BLASTP E = 4 · 10 À150 and Schizosaccharomyces pombe PPA1 BLASTP E = 2 · 10 À123 ) may be involved in phosphate turnover. PPA1 is a cytoplasmic enzyme that is essential for growth (Kolakowski et al, 1988;Lundin et al, 1991) and is required for the hydrolysis of inorganic pyrophosphate to two molecules of orthophosphates (Curbo et al, 2006;Lundin et al, 1991). Thus XP_660572.1's increased expression in osmoadapted cells imply a faster turnover of phosphates to be utilized in other cellular signaling pathways that require phosphorylation (Hohmann, 2002).…”

Triphosphate Tunnel Metalloenzyme Function in Senescence Highlights a Biological Diversification of This Protein Superfamily

“…Other organelles, such as mitochondria and peroxisomes, remain active much longer and provide energy for the cell as well as take over a number of metabolic tasks during this process (Keech et al, 2007;Chrobok et al, 2016). While yeast and animals possess mitochondrial PPases (Lundin et al, 1991;Curbo et al, 2006), so far no mitochondrial PPase has been identified in plants. But generally PPases remove pyrophosphate (PP i ) that is created as a byproduct of anabolic processes such as nucleic acid, protein, and carbohydrate synthesis (Gómez-García et al, 2006).…”