Kinetic and structural parameters governing Fic-mediated adenylylation/AMPylation of the Hsp70 chaperone, BiP/GRP78.

Fic (filamentation induced by cAMP) proteins regulate diverse cell signaling events by post-translationally modifying their protein targets, predominantly by the addition of an AMP (adenosine monophosphate). This modification is called Fic-mediated adenylylation or AMPylation. We previously reported that the human Fic protein, HYPE/FicD, is a novel regulator of the unfolded protein response (UPR) that maintains homeostasis in the endoplasmic reticulum (ER) in response to stress from misfolded proteins. Specifically, HYPE regulates UPR by adenylylating the ER chaperone, BiP/GRP78, which serves as a sentinel for UPR activation. Maintaining ER homeostasis is critical for determining cell fate, thus highlighting the importance of the HYPE-BiP interaction. Here, we study the kinetic and structural parameters that determine the HYPE-BiP interaction. By measuring the binding and kinetic efficiencies of HYPE in its activated (Adenylylation-competent) and wild type (de-AMPylation-competent) forms for BiP in its wild type and ATP-bound conformations, we determine that HYPE displays a nearly identical preference for the wild type and ATP-bound forms of BiP in vitro and preferentially de-AMPylates the wild type form of adenylylated BiP. We also show that AMPylation at BiP's Thr366 versus Thr518 sites differentially affect its ATPase activity, and that HYPE does not adenylylate UPR accessory proteins like J-protein ERdJ6. Using molecular docking models, we explain how HYPE is able to adenylylate Thr366 and Thr518 sites in vitro. While a physiological role for AMPylation at both the Thr366 and Thr518 sites has been reported, our molecular docking model supports Thr518 as the structurally preferred modification site. This is the first such analysis of the HYPE-BiP interaction and offers critical insights into substrate specificity and target recognition.

Calcein Release Assay to Measure Membrane Permeabilization by Recombinant Alpha-Synuclein.

Lipid membranes are involved in regulating biochemical and biological processes and in modulating the selective permeability of cells, organelles, and vesicles. Membrane composition, charge, curvature, and fluidity all have concerted effects on cellular signaling and homeostasis. The ability to prepare artificial lipid assemblies that mimic biological membranes has enabled investigators to obtain considerable insight into biomolecule-membrane interactions. Lipid nanoscale assemblies can vary greatly in size and composition and can consist of a single lipid monolayer, a bilayer, or other more complex assemblies. This structural diversity makes liposomes suitable for a wide variety of biochemical and clinical applications. Here, we describe a calcein dye leakage assay that we have developed to monitor phospholipid vesicle disruption by alpha-synuclein (αSyn), a presynaptic protein that plays a central role in Parkinson's disease (PD). We present data showing the effect of adenylylation of αSyn on αSyn-mediated vesicle disruption as an example. This assay can be used to study the effect of mutations or post-translational modifications on αSyn-membrane interactions, to identify protein binding partners or chemical entities that perturb these interactions, and to study the effects of different lipids on the permeabilization activity of αSyn or any other protein.

Alpha-Synuclein Is a Target of Fic-Mediated Adenylylation/AMPylation: Possible Implications for Parkinson's Disease.

During disease, cells experience various stresses that manifest as an accumulation of misfolded proteins and eventually lead to cell death. To combat this stress, cells activate a pathway called unfolded protein response that functions to maintain endoplasmic reticulum (ER) homeostasis and determines cell fate. We recently reported a hitherto unknown mechanism of regulating ER stress via a novel post-translational modification called Fic-mediatedadenylylation/AMPylation. Specifically, we showed that the human Fic (filamentation induced by cAMP) protein, HYPE/FicD, catalyzes the addition of an adenosine monophosphate (AMP) to the ER chaperone, BiP, to alter the cell's unfolded protein response-mediated response to misfolded proteins. Here, we report that we have now identified a second target for HYPE-alpha-synuclein (αSyn), a presynaptic protein involved in Parkinson's disease. Aggregated αSyn has been shown to induce ER stress and elicit neurotoxicity in Parkinson's disease models. We show that HYPE adenylylates αSyn and reduces phenotypes associated with αSyn aggregation invitro, suggesting a possible mechanism by which cells cope with αSyn toxicity.