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Elife. 2015 Mar 16;4. doi: 10.7554/eLife.04871.

G-actin provides substrate-specificity to eukaryotic initiation factor 2α holophosphatases.

Author information

1
Cambridge Institute for Medical Research, University of Cambridge, Cambridge, United Kingdom.

Abstract

Dephosphorylation of eukaryotic translation initiation factor 2a (eIF2a) restores protein synthesis at the waning of stress responses and requires a PP1 catalytic subunit and a regulatory subunit, PPP1R15A/GADD34 or PPP1R15B/CReP. Surprisingly, PPP1R15-PP1 binary complexes reconstituted in vitro lacked substrate selectivity. However, selectivity was restored by crude cell lysate or purified G-actin, which joined PPP1R15-PP1 to form a stable ternary complex. In crystal structures of the non-selective PPP1R15B-PP1G complex, the functional core of PPP1R15 made multiple surface contacts with PP1G, but at a distance from the active site, whereas in the substrate-selective ternary complex, actin contributes to one face of a platform encompassing the active site. Computational docking of the N-terminal lobe of eIF2a at this platform placed phosphorylated serine 51 near the active site. Mutagenesis of predicted surface-contacting residues enfeebled dephosphorylation, suggesting that avidity for the substrate plays an important role in imparting specificity on the PPP1R15B-PP1G-actin ternary complex.

KEYWORDS:

E. coli; biochemistry; biophysics; cell lines; human; mouse; rabbit; structural biology

PMID:
25774600
PMCID:
PMC4394352
DOI:
10.7554/eLife.04871
[Indexed for MEDLINE]
Free PMC Article

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