title: FICD acts bifunctionally to AMPylate and de-AMPylate the endoplasmic reticulum chaperone BiP.
abstract: Protein folding homeostasis in the endoplasmic reticulum (ER) is defended by an unfolded protein response that matches ER chaperone capacity to the burden of unfolded proteins. As levels of unfolded proteins decline, a metazoan-specific FIC-domain-containing ER-localized enzyme (FICD) rapidly inactivates the major ER chaperone BiP by AMPylating T518. Here we show that the single catalytic domain of FICD can also release the attached AMP, restoring functionality to BiP. Consistent with a role for endogenous FICD in de-AMPylating BiP, FICD-/-hamster cells are hypersensitive to introduction of a constitutively AMPylating, de-AMPylation-defective mutant FICD. These opposing activities hinge on a regulatory residue, E234, whose default state renders FICD a constitutive de-AMPylase in vitro. The location of E234 on a conserved regulatory helix and the mutually antagonistic activities of FICD in vivo, suggest a mechanism whereby fluctuating unfolded protein load actively switches FICD from a de-AMPylase to an AMPylase.
authors.affiliation: Cambridge Institute for Medical Research, University of Cambridge, Cambridge, United Kingdom.
authors.forename: Steffen
authors.initials: S
authors.lastname: Preissler
authors.affiliation: Cambridge Institute for Medical Research, University of Cambridge, Cambridge, United Kingdom.
authors.forename: Claudia
authors.initials: C
authors.lastname: Rato
authors.affiliation: Cambridge Institute for Medical Research, University of Cambridge, Cambridge, United Kingdom.
authors.forename: Luke
authors.initials: L
authors.lastname: Perera
authors.affiliation: Institute of Metabolic Science, University of Cambridge, Cambridge, United Kingdom.
authors.forename: Vladimir
authors.initials: V
authors.lastname: Saudek
authors.affiliation: Cambridge Institute for Medical Research, University of Cambridge, Cambridge, United Kingdom.
authors.forename: David
authors.initials: D
authors.lastname: Ron
mesh_terms: D000249:Adenosine Monophosphate / Q000378:metabolism; D000818:Animals; D055162:Biocatalysis; D016466:CHO Cells; D002352:Carrier Proteins / Q000737:chemistry / Q000502:physiology*; D020134:Catalytic Domain; D006224:Cricetinae; D003412:Cricetulus; D000091342:Endoplasmic Reticulum Chaperone BiP; D057809:HEK293 Cells; D006360:Heat-Shock Proteins / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008565:Membrane Proteins / Q000737:chemistry / Q000502:physiology*; D009713:Nucleotidyltransferases; D011485:Protein Binding; D011499:Protein Processing, Post-Translational
chemical_list: D002352:Carrier Proteins; D000091342:Endoplasmic Reticulum Chaperone BiP; D006360:Heat-Shock Proteins; D008565:Membrane Proteins; D000249:Adenosine Monophosphate; C541422:FICD protein, human; D009713:Nucleotidyltransferases