8.A.27 The CDC50 P-type ATPase Lipid Flippase β-Subunit (CDC50) Family
The first characterized member of the phospholipid importer β-subunit of phospholipid-translocating P-type ATPases is the Lem3 (ligand-effect modulator 3) (YNL323W) protein of Saccharomyces cerevisiae defined as the PLI-β family (Hanson et al., 2003). This protein was reported to be responsible for the import of alkylphosphocholine drugs such as edelfosine and miltefosine which have been used in the treatment of protozoal and fungal diseases, particularly leishmaniasis. Mutational loss of Lem3 results in poor uptake of these drugs as well as of fluorescent, short chain, 7-nitrobenz-2-oxo-1,3-diazol-4-yl (NBD)-labeled phosphatidylcholine and NBD-phosphatidylethanolamine. Phosphatidylserine transport appeared to be normal in a lem3 mutant. Lem3 is the prototype for a large family of eukaryotic proteins found in animals, plants, fungi, slime molds, ciliates and protozoans but not in prokaryotes. Lem3 (414 aas) has 2 putative TMSs at residues 74-95 and 373-394 and is homologous to the putative S. cerevisiae cell division protein, Cdc50 (391 aas; P25656) and an uncharacterized paralogue, Ynr048w of 393 aas; P53740. Lem3 serves as the β-subunit for both Dnf1 (3.A.3.8.4) and Dnf2 (3.A.3.8.5), two phospholipid flipping P-type ATPases in S. cerevisiae (Riekhof and Voelker, 2006). These proteins may generally be β-subunits of phospholipid-translocating P-type ATPases (Lenoir et al., 2009). The beta-subunit, CDC50A, allows the stable expression, assembly, subcellular localization, and lipid transport activity of the P4-ATPase ATP8A2 (Coleman and Molday, 2011).
Cdc50 is a family of conserved eukaryotic proteins that interact with P4-ATPases (phospholipid translocases). Cdc50 association is essential for endoplasmic reticular export of P4-ATPases and proper translocase activity. García-Sánchez et al. 2014 analysed the role of Leishmania infantum LiRos3, the Cdc50 subunit of the P4-ATPase miltefosine transporter (LiMT), on trafficking and complex functionality using site-directed mutagenesis and domain substitution. They identified 22 invariant residues in the Cdc50 proteins from L. infantum, human and yeast. Seven of these residues are found in the extracellular domain of LiRos3, the conservation of which is critical for ensuring that LiMT arrives at the plasma membrane. The substitution of other invariant residues affected complex trafficking to a lesser extent. Invariant residues located in the N-terminal cytosolic domain play a role in transport activity. Partial N-glycosylation of LiRos3 reduced miltefosine transport, and total N-deglycosylation completely inhibited LiMT trafficking to the plasma membrane. One of the N-glycosylation residues proved to be invariant amoung members of the Cdc50 family. The transmembrane and exoplasmic domains are not interchangeable with the other two L. infantum Cdc50 proteins to maintain LiMT interaction. These findings indicate that both invariant and N-glycosylated residues of LiRos3 are involved in LiMT trafficking and transport activity (βGarcía-Sánchez et al. 2014).
The cell division control Cdc50 protein of 391 aas and 3 TMSs. It is an endosomal protein that regulates polarized cell growth (Misu et al. 2003).
Cdc50 of Saccharomyces cerevisiae (P25656)
The miltefosine transporter β-subunit, LdRos3, of phospholipid transporting P-type ATPase-3, LdMT (see TC# 3.A.3.8.19) (Peréz-Victoria et al., 2006; Perandrés-López et al. 2018).
LdRos3 of Leishmania donovani (365 aas; ABB05176)
CDC50A or TMEM30A of 361 aas and 2 TMSs. Required for targetting of the ATP11C ATPase (3.A.3.8.14) and probably several other phospholipid flipping ATPases to the plasma membrane, and possibly also for their activities (Segawa et al. 2014). Forms a heterodimer with ATP8B1 (van der Mark et al. 2014). Signaling networks are regulated by TMEM30A during cell migration, reflecting the regulatory mechanisms underlying tumor migration (Wang et al. 2017). TMEM30A deficiency leads to intrahepatic cholestasis in mice by impairing the expression and localization of bile salt transporters and the expression of related nuclear receptors (Liu et al. 2017).
CDC50A of Homo sapiens
CDC50B or TMEM30B of 351 aas and 2 TMSs. CDC50 homologues are required for plasma membrane targetting and activity of phospholipid flipping ATPases of subfamily 3.A.3.8 (Segawa et al. 2014).
CDC50B of Homo sapiens
Non-catalytic subunit of the Dnf3 PL-flipping P-type ATPase (TC# 3.A.3.8.20), Crf1 of 393 aas and 2 TMSs at the N- and C-termini. Also required for nutrient uptake at low temperatures (Tokai et al. 2000).
Crf1 of Saccharomyces cerevisiae