ATP13A2 is a lysosomal P-type transport ATPase that has been implicated in Kufor-Rakeb syndrome and Parkinson's disease (PD), providing protection against α-synuclein, Mn 2+ , and Zn 2+ toxicity in various model systems. So far, the molecular function and regulation of ATP13A2 remains undetermined. Here, we demonstrate that ATP13A2 contains a unique N-terminal hydrophobic extension that lies on the cytosolic membrane surface of the lysosome, where it interacts with the lysosomal signaling lipids phosphatidic acid (PA) and phosphatidylinositol(3,5)bisphosphate [PI(3,5)P2]. We further demonstrate that ATP13A2 accumulates in an inactive autophosphorylated state and that PA and PI(3,5)P2 stimulate the autophosphorylation of ATP13A2. In a cellular model of PD, only catalytically active ATP13A2 offers cellular protection against rotenone-induced mitochondrial stress, which relies on the availability of PA and PI(3,5)P2. Thus, the N-terminal binding of PA and PI(3,5)P2 emerges as a key to unlock the activity of ATP13A2, which may offer a therapeutic strategy to activate ATP13A2 and thereby reduce α-synuclein toxicity or mitochondrial stress in PD or related disorders.mitochondria | lysosome | flippase | α-synuclein | P5-type ATPase N euronal fitness depends on optimal lysosomal function and efficient lysosomal delivery of proteins and organelles by autophagy for subsequent breakdown (1, 2). Kufor-Rakeb syndrome (KRS) is an autosomal recessive form of Parkinson's disease (PD) associated with dementia, which is caused by mutations in ATP13A2/PARK9 (3). Mutations in or knockdown (KD) of ATP13A2 lead to lysosomal dysfunctions, including reduced lysosomal acidification, decreased degradation of lysosomal substrates (4), impaired autophagosomal flux (4, 5), and accumulation of fragmented mitochondria (5, 6). By contrast, overexpression (OE) of Ypk9p (i.e., the yeast ATP13A2 ortholog) protects yeast against toxicity of α-synuclein (7), which is the major protein in Lewy bodies, the abnormal protein aggregates that develop inside nerve cells in PD. This protective effect of ATP13A2 on α-synuclein toxicity is conserved in yeast, Caenorhabditis elegans, and rat neuronal cells (7). Because ATP13A2 imparts resistance to Mn 2+ (7-9) and Zn 2+ (10-12), it was proposed that ATP13A2 may function as a Mn 2+ (7-9) and/or Zn 2+ transporter (10-12).ATP13A2 belongs to the P5 subfamily of the P-type ATPase superfamily, which comprises five subfamilies (P1-5) of membrane transporters. P-type ATPases hydrolyze ATP to actively transport inorganic ions across membranes or lipids between membrane leaflets (reviewed in ref. 13). During the transport cycle, a phosphointermediate is formed on a conserved aspartate residue (14). The human P5-type ATPases are divided into two groups, P5A (ATP13A1) and P5B (ATP13A2-5), but their transport specificity has not been established (14-16).P-type ATPases comprise a membrane-embedded core of six transmembrane (TM) helices (M1-6) that form the substrate binding site(s) and entrance/exit pathways for the transp...

Hereditary spastic paraplegias are heterogeneous neurodegenerative disorders characterized by progressive spasticity of the lower limbs due to degeneration of the corticospinal motor neurons. In a Bulgarian family with three siblings affected by complicated hereditary spastic paraplegia, we performed whole exome sequencing and homozygosity mapping and identified a homozygous p.Thr512Ile (c.1535C > T) mutation in ATP13A2. Molecular defects in this gene have been causally associated with Kufor-Rakeb syndrome (#606693), an autosomal recessive form of juvenile-onset parkinsonism, and neuronal ceroid lipofuscinosis (#606693), a neurodegenerative disorder characterized by the intracellular accumulation of autofluorescent lipopigments. Further analysis of 795 index cases with hereditary spastic paraplegia and related disorders revealed two additional families carrying truncating biallelic mutations in ATP13A2. ATP13A2 is a lysosomal P5-type transport ATPase, the activity of which critically depends on catalytic autophosphorylation. Our biochemical and immunocytochemical experiments in COS-1 and HeLa cells and patient-derived fibroblasts demonstrated that the hereditary spastic paraplegia-associated mutations, similarly to the ones causing Kufor-Rakeb syndrome and neuronal ceroid lipofuscinosis, cause loss of ATP13A2 function due to transcript or protein instability and abnormal intracellular localization of the mutant proteins, ultimately impairing the lysosomal and mitochondrial function. Moreover, we provide the first biochemical evidence that disease-causing mutations can affect the catalytic autophosphorylation activity of ATP13A2. Our study adds complicated hereditary spastic paraplegia (SPG78) to the clinical continuum of ATP13A2-associated neurological disorders, which are commonly hallmarked by lysosomal and mitochondrial dysfunction. The disease presentation in our patients with hereditary spastic paraplegia was dominated by an adult-onset lower-limb predominant spastic paraparesis. Cognitive impairment was present in most of the cases and ranged from very mild deficits to advanced dementia with fronto-temporal characteristics. Nerve conduction studies revealed involvement of the peripheral motor and sensory nerves. Only one of five patients with hereditary spastic paraplegia showed clinical indication of extrapyramidal involvement in the form of subtle bradykinesia and slight resting tremor. Neuroimaging cranial investigations revealed pronounced vermian and hemispheric cerebellar atrophy. Notably, reduced striatal dopamine was apparent in the brain of one of the patients, who had no clinical signs or symptoms of extrapyramidal involvement.

Heavy metal pumps (P1B-ATPases) are important for cellular heavy metal homeostasis. AtHMA4, an Arabidopsis thaliana heavy metal pump of importance for plant Zn 2؉ nutrition, has an extended C-terminal domain containing 13 cysteine pairs and a terminal stretch of 11 histidines. Using a novel size-exclusion chromatography, inductively coupled plasma mass spectrometry approach we report that the C-terminal domain of AtHMA4 is a high affinity Zn 2؉ P1B-type ATPases form a subfamily of P-type ATPases and pump metal ions across biological membranes (1-4). These pumps maintain metal homeostasis in all domains of life (5-8).Humans have only two P1B-ATPases, namely ATP7A and ATP7B, both of which transport Cu ϩ , and cause Menke and Wilson diseases, respectively, when mutated (8). In contrast, in the model plant Arabidopsis thaliana eight P1B-ATPase genes (heavy metal ATPases 1-8 (HMA1-HMA8)3 ) are present (9, 10). Monovalent metal ions, such as Cu ϩ and Ag ϩ , are transported by HMA5-HMA8, which belong to the subclass P1B1, whereas divalent metal ions, such as Zn 2ϩ and Cd 2ϩ , are transported by HMA2-HMA4 belonging to the P1B2 subgroup that is related to prokaryotic divalent heavy metal pumps (4, 11).In A. thaliana, HMA2 and HMA4 are closely related in primary sequence and might have evolved as a result of gene duplication (10). In the physiology of A. thaliana, these two pumps are redundant in several functions (12, 13). Both genes are expressed in roots in the pericycle cells surrounding the xylem, a vascular tissue specialized in transport of inorganic nutrients and water to the shoot. Single knock-out mutants of AtHMA2 and AtHMA4 have weak phenotypes, whereas a double hma2 hma4 mutant accumulates zinc in root pericycle cells, which causes shoots to suffer from zinc deficiency. This strongly suggests that AtHMA2 and AtHMA4 are responsible for catalyzing zinc efflux from pericycle cells, thereby loading the xylem with zinc (12-13). In the zinc hyperaccumulator Arabidopsis halleri the gene encoding HMA4 has been copied three times (14). This, together with increased promoter strength, results in an increased capacity of this metallophyte to accumulate zinc in shoots (14).P1B-ATPases have six to eight transmembrane segments responsible for metal ion coordination during transport, a large cytosolic portion divided into three catalytic domains (A, P, and N), and two terminal domains that contain metal-coordinating residues (the N terminus and the C terminus). The N-terminal domains of P1B-ATPases are not essential for the transport mechanism but play important roles in their post-translational regulation. In bacterial P1B-ATPases the N-terminal domains are characterized by Cys-X-X-Cys sequences (4,7,8,15). The Cys residues are responsible for metal coordination and can be involved in binding both monovalent (Ag ϩ and Cu ϩ ) and divalent metal cations (Cu 2ϩ , Cd 2ϩ , and Zn 2ϩ ) (16 -21). In plant Zn 2ϩ -ATPases the Cys-X-X-Cys conserved sequence is replaced by a Cys-Cys-X-X-Glu motif (9,12,22,23). Truncation of P1B-ATP...

P5A ATPases are expressed in the endoplasmic reticulum (ER) of all eukaryotic cells, and their disruption results in severe ER stress. However, the function of these ubiquitous membrane proteins, which belong to the P-type ATPase superfamily, is unknown. We purified a functional tagged version of the Saccharomyces cerevisiae P5A ATPase Spf1p and observed that the ATP hydrolytic activity of the protein is stimulated by phosphatidylinositol 4-phosphate (PI4P). Furthermore, SPF1 exhibited negative genetic interactions with SAC1, encoding a PI4P phosphatase, and with OSH1 to OSH6, encoding Osh proteins, which, when energized by a PI4P gradient, drive export of sterols and lipids from the ER. Deletion of SPF1 resulted in increased sensitivity to inhibitors of sterol production, a marked change in the ergosterol/lanosterol ratio, accumulation of sterols in the plasma membrane, and cytosolic accumulation of lipid bodies. We propose that Spf1p maintains cellular sterol homeostasis by influencing the PI4P-induced and Osh-mediated export of sterols from the ER.

Evolution of P5 type ATPases marks the origin of eukaryotes but still they remain the least characterized pumps in the superfamily of P-type ATPases. Phylogenetic analysis of available sequences suggests that P5 ATPases should be divided into at least two subgroups, P5A and P5B. P5A ATPases have been identified in the endoplasmic reticulum and seem to have basic functions in protein maturation and secretion. P5B ATPases localize to vacuolar/lysosomal or apical membranes and in animals play a role in hereditary neuronal diseases. Here we have used a bioinformatical approach to identify differences in the primary sequences between the two subgroups. P5A and P5B ATPases appear have a very different membrane topology from other P-type ATPases with two and one, respectively, additional transmembrane segments inserted in the N-terminal end. Based on conservation of residues in the transmembrane region, the two P5 subgroups most likely have different substrate specificities although these cannot be predicted from their sequences. Furthermore, sequence differences between P5A and P5B ATPases are identified in the catalytic domains that could influence key kinetic properties differentially. Together these findings indicate that P5A and P5B ATPases are structurally and functionally different.

Several human P5-type transport ATPases are implicated in neurological disorders, but little is known about their physiological function and properties. Here, we investigated the relationship between the five mammalian P5 isoforms ATP13A1-5 in a comparative study. We demonstrated that ATP13A1-4 isoforms undergo autophosphorylation, which is a hallmark P-type ATPase property that is required for substrate transport. A phylogenetic analysis of P5 sequences revealed that ATP13A1 represents clade P5A, which is highly conserved between fungi and animals with one member in each investigated species. The ATP13A2-5 isoforms belong to clade P5B and diversified from one isoform in fungi and primitive animals to a maximum of four in mammals by successive gene duplication events in vertebrate evolution. We revealed that ATP13A1 localizes in the endoplasmic reticulum (ER) and experimentally demonstrate that ATP13A1 likely contains 12 transmembrane helices. Conversely, ATP13A2-5 isoforms reside in overlapping compartments of the endosomal system and likely contain 10 transmembrane helices, similar to what was demonstrated earlier for ATP13A2. ATP13A1 complemented a deletion of the yeast P5A ATPase SPF1, while none of ATP13A2-5 could complement either the loss of SPF1 or that of the single P5B ATPase YPK9 in yeast. Thus, ATP13A1 carries out a basic ER function similar to its yeast counterpart Spf1p that plays a role in ER related processes like protein folding and processing. ATP13A2-5 isoforms diversified in mammals and are expressed in the endosomal system where they may have evolved novel complementary or partially redundant functions. While most P5-type ATPases are widely expressed, some P5B-type ATPases (ATP13A4 and ATP13A5) display a more limited tissue distribution in the brain and epithelial glandular cells, where they may exert specialized functions. At least some P5B isoforms are of vital importance for the nervous system, since ATP13A2 and ATP13A4 are linked to respectively Parkinson disease and autism spectrum disorders.

Mutations in ATP13A2 lead to Kufor-Rakeb syndrome, a parkinsonism with dementia. ATP13A2 belongs to the P-type transport ATPases, a large family of primary active transporters that exert vital cellular functions. However, the cellular function and transported substrate of ATP13A2 remain unknown. To discuss the role of ATP13A2 in neurodegeneration, we first provide a short description of the architecture and transport mechanism of P-type transport ATPases. Then, we briefly highlight key P-type ATPases involved in neuronal disorders such as the copper transporters ATP7A (Menkes disease), ATP7B (Wilson disease), the Na+/K+-ATPases ATP1A2 (familial hemiplegic migraine) and ATP1A3 (rapid-onset dystonia parkinsonism). Finally, we review the recent literature of ATP13A2 and discuss ATP13A2's putative cellular function in the light of what is known concerning the functions of other, better-studied P-type ATPases. We critically review the available data concerning the role of ATP13A2 in heavy metal transport and propose a possible alternative hypothesis that ATP13A2 might be a flippase. As a flippase, ATP13A2 may transport an organic molecule, such as a lipid or a peptide, from one membrane leaflet to the other. A flippase might control local lipid dynamics during vesicle formation and membrane fusion events.

Identification of the substrate of P5A-ATPases would throw light on an important general process in the ER that is still not fully understood. This article is part of a Special Issue entitled Structural biochemistry and biophysics of membrane proteins.