< Back to previous page

Project

Physiological role of the ATP13A2 gene product. A putative Mn2+ transporter.

The P5‐type ATPases are a subfamily belonging to the large family of P‐type transporters and are probably the least characterized. One of the most intriguing members is ATP13A2, a lysosomal membrane protein in which mutations underlie various neurological disorders, including Kufor‐Rakeb syndrome, Neuronal Ceroid Lipofuscinosis and Early‐Onset Parkinson’s Disease. It has previously been described that ATP13A2 deficiency is involved in a plethora of lysosomal and mitochondrial dysfunctions and numerous substrates have been proposed to be transported by the pump, varying from ions such as Mn2+ or Zn2+ to lipids, as is seen in the P4 ATPase subfamily.

Based on sequence comparison the P5 ATPases can be divided into two distinct groups, the P5A (ATP13A1) and the P5B (ATP13A2‐5) and this subdivision further reflects in various other characteristics. Indeed, we demonstrated the P5A ATPases to be localized in the endoplasmic reticum, whereas the P5B associate with the endo‐/lysosomal system. More specifically, ATP13A2 and ATP13A4 are targeted to the late endo‐/lysosomes, ATP13A3 is found in the early and recycling endosomes. We furthermore confirmed the predicted topology for the P5A, consisting of 12 transmembrane (TM) helices with the two N‐terminal helices Mb and Ma assembling a hairpin spanning the membrane. On the contrary, although the P5B were predicted to hold 11 TM helices, with N‐ and C‐terminal ends on opposite sides of the membrane, we refuted this topology and found the P5B to be built out of 10 TM helices and one additional N‐terminal helix, firmly associated with the membrane. For the first time, we established a biochemical assay for the P5B, defining the amount of phosphorylation. We could demonstrate the formation of a phospho‐intermediate for ATP13A1‐4, pointing to active enzymes. The assay now provides us with an indispensable tool for further research of the P5 ATPases and their disease mutants. It should be noted that it was very difficult to obtain consistent results for ATP13A5.

The presence of the additional membrane‐associated N‐terminal helix in ATP13A2, is a peculiar feature, which is entitled to be investigated more profound. Via protein‐lipid overlays, flotation assays and sequence mutagenesis, the N‐terminal helix Ma was shown to interact with two signaling lipids, i.e. phosphatidic acid (PA) and phosphatidylinositol(3,5)‐bisphosphate (PI(3,5)P2). Moreover, binding of these lipids activates the protein, which is otherwise pending in the E1P state, awaiting further activation. Markedly, the catalytic active enzyme encompasses an even more noticeable function as it provides protection against rotenone‐induced mitochondrial stress upon binding of PA and PI(3,5)P2. Depletion of one of these two lipids, abolishes the protective effect. This emphasizes the importance of the N‐terminus in this process and implicates the interaction of PA and PI(3,5)P2 with N‐terminus to offer a therapeutic strategy for protection against mitochondrial stress, one of the important distinctive features of Parkinson’s Disease or related disorders.

In spite of the fact that ATP13A2 is implicated in various disorders, no substantial biochemical evidence was present up until now. We here provided the first biochemical proof that disease mutations can indeed affect the catalytic activity of the pump as they display an impaired autophosphorylation. Finally, we also demonstrated ATP13A2 mutations to underlie a different neurological pathology, i.e. Hereditary Spastic Paraplegia.

For ATP13A2, it is becoming more and more clear that it plays an emerging and significant role in neurological disorders.

Date:15 Sep 2009 →  18 Oct 2016
Keywords:manganese, Kufor-Rakeb, Parkinson, P5-type ATPases
Disciplines:Physiology, Biophysics
Project type:PhD project