Cytosolic Arl2 Is Complexed with Cofactor D and Protein Phosphatase 2A

Academic Article

Abstract

  • Arl2 is a member of the ADP-ribosylation factor family of 20-kDa GTPases that is highly conserved in eukaryotes. Recent results revealed that a portion of cellular Arl2 and its binding partner, BART, localize to mitochondria. Because ∼90% of cellular Arl2 is cytosolic, we investigated properties of the soluble protein and found that it is stably bound in a complex that migrates in gel filtration medium with a predicted molecular mass of ∼300 kDa. This complex was purified ∼500-fold from the soluble fraction of bovine brain. Protein components were identified by mass spectroscopy and revealed the presence of four other proteins that include the tubulin folding cochaperone cofactor D and all three subunits of at least two protein phosphatase 2A (PP2A) protein phosphatase trimers. The presence of more than one PP2A B-type subunit and the low stoichiometry of Arl2 indicate that the purified preparation still contains a mixture of complexes that cannot currently be completely resolved. Thus, although all the soluble Arl2 in bovine brain is in high molecular mass complexes, only a portion of the total cellular cofactor D and PP2A are associated with the Arl2. We further show that the Arl2 in the complex cannot bind GTP and that complexed cofactor D does not efficiently participate in tubulin refolding reactions in a manner comparable with free cofactor D. Our data suggest functional roles for the cytosolic Arl2 complex in modulating tubulin and microtubule behavior as well as a possible role in apoptosis.
  • Authors

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    Digital Object Identifier (doi)

    Author List

  • Shern JF; Sharer JD; Pallas DC; Bartolini F; Cowan NJ; Reed MS; Pohl J; Kahn RA
  • Start Page

  • 40829
  • End Page

  • 40836
  • Volume

  • 278
  • Issue

  • 42