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J Biol Chem. 2012 Oct 19;287(43):36041-50. doi: 10.1074/jbc.M112.370403. Epub 2012 Aug 16.

Molecular events initiating exit of a copper-transporting ATPase ATP7B from the trans-Golgi network.

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1
Department of Physiology, Johns Hopkins University, Baltimore, Maryland 21205, USA.

Abstract

The copper-transporting ATPase ATP7B has a dual intracellular localization: the trans-Golgi network (TGN) and cytosolic vesicles. Changes in copper levels, kinase-mediated phosphorylation, and mutations associated with Wilson disease alter the steady-state distribution of ATP7B between these compartments. To identify a primary molecular event that triggers ATP7B exit from the TGN, we characterized the folding, activity, and trafficking of the ATP7B variants with mutations within the regulatory N-terminal domain (N-ATP7B). We found that structural changes disrupting the inter-domain contacts facilitate ATP7B exit from the TGN. Mutating Ser-340/341 in the N-ATP7B individually or together to Ala, Gly, Thr, or Asp produced active protein and shifted the steady-state localization of ATP7B to vesicles, independently of copper levels. The Ser340/341G mutant had a lower kinase-mediated phosphorylation under basal conditions and no copper-dependent phosphorylation. Thus, negative charges introduced by copper-dependent phosphorylation are not obligatory for ATP7B trafficking from the TGN. The Ser340/341A mutation did not alter the overall fold of N-ATP7B, but significantly decreased interactions with the nucleotide-binding domain, mimicking consequences of copper binding to N-ATP7B. We propose that structural changes that specifically alter the inter-domain contacts initiate exit of ATP7B from the TGN, whereas increased phosphorylation may be needed to maintain an open interface between the domains.

PMID:
22898812
PMCID:
PMC3476272
DOI:
10.1074/jbc.M112.370403
[Indexed for MEDLINE]
Free PMC Article
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