Browsing by Author "Dittmar, Gunnar"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    The lipid head group is the key element for substrate recognition by the P4 ATPase ALA2: a phosphatidylserine flippase
    (Portland Press, 2019-03-06) Theorin, Lisa; Faxén, Kristina; Sørensen, Danny Mollerup; Migotti, Rebekka; Dittmar, Gunnar; Schiller, Jürgen; Daleke, David L.; Palmgren, Michael; López-Marqués, Rosa Laura; Pomorski, Thomas Günther; Biochemistry and Molecular Biology, School of Medicine
    Type IV P-type ATPases (P4 ATPases) are lipid flippases that catalyze phospholipid transport from the exoplasmic to the cytoplasmic leaflet of cellular membranes, but the mechanism by which they recognize and transport phospholipids through the lipid bilayer remains unknown. In the present study, we succeeded in purifying recombinant aminophospholipid ATPase 2 (ALA2), a member of the P4 ATPase subfamily in Arabidopsis thaliana, in complex with the ALA-interacting subunit 5 (ALIS5). The ATP hydrolytic activity of the ALA2-ALIS5 complex was stimulated in a highly specific manner by phosphatidylserine. Small changes in the stereochemistry or the functional groups of the phosphatidylserine head group affected enzymatic activity, whereas alteration in the length and composition of the acyl chains only had minor effects. Likewise, the enzymatic activity of the ALA2-ALIS5 complex was stimulated by both mono- and di-acyl phosphatidylserines. Taken together, the results identify the lipid head group as the key structural element for substrate recognition by the P4 ATPase.
  • Thumbnail Image
    Item
    Stable Isotope-Assisted Untargeted Metabolomics Identifies ALDH1A1-Driven Erythronate Accumulation in Lung Cancer Cells
    (MDPI, 2023-10-19) Zhang, Jie; Keibler, Mark A.; Dong, Wentao; Ghelfi, Jenny; Cordes, Thekla; Kanashova, Tamara; Pailot, Arnaud; Linster, Carole L.; Dittmar, Gunnar; Metallo, Christian M.; Lautenschlaeger, Tim; Hiller, Karsten; Stephanopoulos, Gregory; Radiation Oncology, School of Medicine
    Using an untargeted stable isotope-assisted metabolomics approach, we identify erythronate as a metabolite that accumulates in several human cancer cell lines. Erythronate has been reported to be a detoxification product derived from off-target glycolytic metabolism. We use chemical inhibitors and genetic silencing to define the pentose phosphate pathway intermediate erythrose 4-phosphate (E4P) as the starting substrate for erythronate production. However, following enzyme assay-coupled protein fractionation and subsequent proteomics analysis, we identify aldehyde dehydrogenase 1A1 (ALDH1A1) as the predominant contributor to erythrose oxidation to erythronate in cell extracts. Through modulating ALDH1A1 expression in cancer cell lines, we provide additional support. We hence describe a possible alternative route to erythronate production involving the dephosphorylation of E4P to form erythrose, followed by its oxidation by ALDH1A1. Finally, we measure increased erythronate concentrations in tumors relative to adjacent normal tissues from lung cancer patients. These findings suggest the accumulation of erythronate to be an example of metabolic reprogramming in cancer cells, raising the possibility that elevated levels of erythronate may serve as a biomarker of certain types of cancer.