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The degradation (by distinct pathways) of human d ‐amino acid oxidase and its interacting partner pLG 72 – two key proteins in d ‐serine catabolism in the brain
Author(s) -
Cappelletti Pamela,
Campomenosi Paola,
Pollegioni Loredano,
Sacchi Silvia
Publication year - 2014
Publication title -
the febs journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.981
H-Index - 204
eISSN - 1742-4658
pISSN - 1742-464X
DOI - 10.1111/febs.12616
Subject(s) - serine , biochemistry , cytosol , d amino acid oxidase , allosteric regulation , proteasome , catabolism , peroxisome , ubiquitin , chemistry , microbiology and biotechnology , biology , oxidase test , receptor , enzyme , gene
Human d ‐amino acid oxidase ( EC 1.4.3.3 ; hDAAO ) is a peroxisomal flavoenzyme significantly enriched in the mammalian brain. hDAAO has been proposed to play (with serine racemase; EC 5.1.1.18 ) an essential role in the catabolism of d ‐serine, an ‘atypical’ key signalling molecule that acts as allosteric activator of the N ‐methyl‐ d ‐aspartate‐type glutamate receptor ( NMDAr ). hDAAO and its interacting partner pLG 72 have been related to schizophrenia, a highly disabling psychiatric disorder in which a dysfunction of NMDA ‐mediated neurotransmission is widely assumed to occur. We previously demonstrated that the d ‐serine cellular concentration depends on hDAAO and pLG 72 expression levels and that newly‐synthesized hDAAO interacts with its modulator in the cytosol, being progressively destabilized and inactivated. To obtain insight into the mechanisms regulating cellular d ‐serine levels, we investigated the degradation pathways of hDAAO and pLG 72 in U 87 glioblastoma cells stably expressing enhanced yellow fluorescent protein‐ hDAAO (peroxisomal), hDAAO ‐enhanced yellow fluorescent protein (cytosolic) or pLG 72‐enhanced cyan fluorescent protein (mitochondrial) proteins. hDAAO is a long‐lived protein: the peroxisomal fraction of this flavoprotein is degraded via the lysosomal/endosomal pathway (and blocking this pathway increases the cellular hDAAO activity and decreases d ‐serine levels), whereas the cytosolic portion is ubiquitinated and targeted to the proteasome. By contrast, pLG 72 shows a rapid turnover ( t 1/2 ≈ 25–40 min) and is degraded via the proteasome system, albeit not ubiquitinated. Overexpression of pLG 72 increases the turnover of hDAAO , in turn playing a protective role against excessive d ‐serine depletion.