Open AccessMannose 6 Dephosphorylation of Lysosomal Proteins Mediated by Acid Phosphatases Acp2 and Acp5
Author(s) -
G. Makrypidi,
Markus Damme,
Sven MüllerLoennies,
Maria Trusch,
Bernhard Schmidt,
Hartmut Schlüter,
Joerg Heeren,
Torben Lübke,
Paul Säftig,
Thomas Braulke
Publication year - 2012
Publication title -
molecular and cellular biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.14
H-Index - 327
eISSN - 1067-8824
pISSN - 0270-7306
DOI - 10.1128/mcb.06195-11
Subject(s) - dephosphorylation , mannose 6 phosphate , isoelectric point , biology , biochemistry , lysosome , mannose 6 phosphate receptor , acid phosphatase , phosphatase , phosphate , phosphorylation , receptor , enzyme , growth factor
Mannose 6-phosphate (Man6P) residues represent a recognition signal required for efficient receptor-dependent transport of soluble lysosomal proteins to lysosomes. Upon arrival, the proteins are rapidly dephosphorylated. We used mice deficient for the lysosomal acid phosphatase Acp2 or Acp5 or lacking both phosphatases (Acp2/Acp5(-/-)) to examine their role in dephosphorylation of Man6P-containing proteins. Two-dimensional (2D) Man6P immunoblot analyses of tyloxapol-purified lysosomal fractions revealed an important role of Acp5 acting in concert with Acp2 for complete dephosphorylation of lysosomal proteins. The most abundant lysosomal substrates of Acp2 and Acp5 were identified by Man6P affinity chromatography and mass spectrometry. Depending on the presence of Acp2 or Acp5, the isoelectric point of the lysosomal cholesterol-binding protein Npc2 ranged between 7.0 and 5.4 and may thus regulate its interaction with negatively charged lysosomal membranes at acidic pH. Correspondingly, unesterified cholesterol was found to accumulate in lysosomes of cultured hepatocytes of Acp2/Acp5(-/-) mice. The data demonstrate that dephosphorylation of Man6P-containing lysosomal proteins requires the concerted action of Acp2 and Acp5 and is needed for hydrolysis and removal of degradation products.