Covalent Protein Labeling by Enzymatic Phosphocholination

We present a new protein labeling method based on the covalent enzymatic phosphocholination of a specific octapeptide amino acid sequence in intact proteins. The bacterial enzyme AnkX from Legionella pneumophila has been established to transfer functional phosphocholine moieties from synthetically produced CDP‐choline derivatives to N‐termini, C‐termini, and internal loop regions in proteins of interest. Furthermore, the covalent modification can be hydrolytically removed by the action of the Legionella enzyme Lem3. Only a short peptide sequence (eight amino acids) is required for efficient protein labeling and a small linker group (PEG‐phosphocholine) is introduced to attach the conjugated cargo.     

Direct Targeting of Rab‐GTPase–Effector Interactions

Small GTPases are molecular switches using GDP/GTP alternation to control numerous vital cellular processes. Although aberrant function and regulation of GTPases are implicated in various human diseases, direct targeting of this class of proteins has proven difficult, as GTPase signaling and regulation is mediated by extensive and shallow protein interfaces. Here we report the development of inhibitors of protein–protein interactions involving Rab proteins, a subfamily of GTPases, which are key regulators of vesicular transport. Hydrocarbon‐stapled peptides were designed based on crystal structures of Rab proteins bound to their interaction partners. These modified peptides exhibit significantly increased affinities and include a stapled peptide (StRIP3) that selectively binds to activated Rab8a and inhibits a Rab8a–effector interaction in vitro.     

One-pot dual-labeling of a protein by two chemoselective reactions

Dual system for proteins: The site-specific two-color labeling of a Rab GTPase was achieved in a one-pot procedure by combination of chemoselective native chemical ligation and oxime ligation. This strategy could be a general, facile, and efficient method for specific multiple modifications of a given protein. The Rab GTPase biosensor was demonstrated for protein folding and protein-protein interaction studies.     

The Alarmone Diadenosine Tetraphosphate as a Cosubstrate for Protein AMPylation

Diadenosine polyphosphates (Ap_nAs) are non-canonical nucleotides whose cellular concentrations increase during stress and are therefore termed alarmones, signaling homeostatic imbalance. Their cellular role is poorly understood. In this work, we assessed Ap_nAs for their usage as cosubstrates for protein AMPylation, a post-translational modification in which adenosine monophosphate (AMP) is transferred to proteins. In humans, AMPylation mediated by the AMPylator FICD with ATP as a cosubstrate is a response to ER stress. Herein, we demonstrate that Ap₄A is proficiently consumed for AMPylation by FICD. By chemical proteomics using a new chemical probe, we identified new potential AMPylation targets. Interestingly, we found that AMPylation targets of FICD may differ depending on the nucleotide cosubstrate. These results may suggest that signaling at elevated Ap₄A levels during cellular stress differs from when Ap₄A is present at low concentrations, allowing response to extracellular cues.