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An oligomeric state-dependent switch in the ER enzyme FICD regulates AMPylation and deAMPylation of BiP

ABSTRACT: AMPylation is an inactivating modification that alters the activity of the major endoplasmic reticulum (ER) chaperone BiP to match the burden of unfolded proteins. A single ER-localised Fic protein, FICD (HYPE), catalyses both AMPylation and deAMPylation of BiP. However, the basis for the switch in FICD's activity is unknown. We report on the transition of FICD from a dimeric enzyme, that deAMPylates BiP, to a monomer with potent AMPylation activity. Mutations in the dimer interface, or in residues along an inhibitory pathway linking the dimer interface to the enzyme's active site, favour BiP AMPylation in vitro and in cells. Mechanistically, monomerisation relieves a repressive effect allosterically propagated from the dimer interface to the inhibitory Glu234, thereby permitting AMPylation-competent binding of MgATP. Moreover, a reciprocal signal, propagated from the nucleotide binding site, provides a mechanism for coupling the oligomeric-state and enzymatic activity of FICD to the energy status of the ER.

SUBMITTER: Luke, A. Perera

PROVIDER: S-SCDT-EMBOJ-2019-102177 | biostudies-other |

REPOSITORIES: biostudies-other

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Project description:BackgroundHuman BiP is traditionally regarded as a major endoplasmic reticulum (ER) chaperone performing a number of well-described functions in the ER. In recent years it was well established that this molecule can also be located in other cell organelles and compartments, on the cell surface or be secreted. Also novel functions were assigned to this protein. Importantly, BiP protein appears to be involved in cancer and rheumatoid arthritis progression, autoimmune inflammation and tissue damage, and thus could potentially be used for therapeutic purposes. In addition, a growing body of evidence indicates BiP as a new therapeutic target for the treatment of neurodegenerative diseases. Increasing importance of this protein and its involvement in critical human diseases demands new source of high quality native recombinant human BiP for further studies and potential application. Here we introduce yeast Saccharomyces cerevisiae as a host for the generation of human BiP protein.ResultsExpression of a full-length human BiP precursor in S. cerevisiae resulted in a high-level secretion of mature recombinant protein into the culture medium. The newly discovered ability of the yeast cells to recognize, correctly process the native signal sequence of human BiP and secrete this protein into the growth media allowed simple one-step purification of highly pure recombinant BiP protein with yields reaching 10 mg/L. Data presented in this study shows that secreted recombinant human BiP possesses native amino acid sequence and structural integrity, is biologically active and without yeast-derived modifications. Strikingly, ATPase activity of yeast-derived human BiP protein exceeded the activity of E. coli-derived recombinant human BiP by a 3-fold.ConclusionsS. cerevisiae is able to correctly process and secrete human BiP protein. Consequently, resulting recombinant BiP protein corresponds accurately to native analogue. The ability to produce large quantities of native recombinant human BiP in yeast expression system should accelerate the analysis and application of this important protein.

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An oligomeric state-dependent switch in the ER enzyme FICD regulates AMPylation and deAMPylation of BiP

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