Protein ADP-Ribosylation - Herwig Schüler

We are interested in the enzymes that catalyse ADP-ribosylation as well as its removal. Inhibitors of these enzymes are promising for future therapies in cancer, inflammation, and infectious diseases caused by both virus and bacteria.

Illustration of a blue crystal structure
Crystal structure of the Pseudomonas exotoxin ExoS bound to human protein 14-3-3. From Karlberg et al., Nat Commun. 2018 Sep 17;9(1):3785. Illustration: Herwig Schüler

Many proteins in the cells of our body carry so-called post-translational modifications (PTMs). These are chemical modifications, such as phosphate or methyl groups, linked to the amino acid side chains in proteins. They are put in place and removed by specialised enzymes, and they can be read by specialised domains. These modifications can dictate the cellular location or protein activity. Primarily in cancer, but also in other human diseases, these modifications can be disturbed, or we can make use of them to re-direct protein activities. Thus if we understand these modifications and develop drug-like compounds that can influence them, then this can generate powerful therapeutic opportunities.

We study a PTM called ADP-ribosylation. Inside our cells, a family of 17 enzymes called PARPs can ADP-ribosylate other proteins, DNA, and RNA. The first end best understood enzyme, PARP1, is an oncology target; currently 4 PARP inhibitors have been approved for treatment of BRCA-deficient breast and ovarian cancers. Our idea is to study the remaining PARP enzymes of therapeutic interest. We have determined the first crystal structures of 10 of them, and together with collaborators we have developed inhibitors against PARP3, PARP10, PARP11 and PARP14. In our own research we use these compounds to find out more about the cellular functions of the PARP enzymes. We also  explore new therapeutic opportunities. For example, in collaboration with Julian Walfridsson (HERM) and Stefan Deneberg (Huddinge sjukhus) we study the effect of PARP inhibitors in acute myeloid leukemia (AML) cells.

ADP-ribosylated proteins can be recognised by a small protein module called a macrodomain. Some macrodomains can recognise and remove the ADP-ribosyl group. For example, coronavirus non-structural protein 3 (nsp3) contains three macrodomains one of which can remove ADP-ribosyl groups; but the function of this is still unclear. We also study macrodomains, have determined several crystal structures, and have discovered the first drug-like compounds that block macrodomains. We will need a better understanding of the functions of macrodomains and the consequences of their activities, before their therapeutic interest can be evaluated.

The PARP enzymes are related to ADP-ribosylating bacterial toxins, the most well-known of which are pertussis, diphtheria, cholera and botulinum toxins. These toxins all put a chemical modification on proteins in our infected cells in order to create an advantage for the invasive bacteria. Recently we have determined the first crystal structure of a subclass of bacterial toxins, namely, the ones activated by the human protein 14-3-3. We could also demonstrate how 14-3-3 activates the toxins ExoS and ExoT from Pseudomonas, a multi drug resistant bacteria that often causes problematic infections in hospital environments. Currently we are looking for inhibitors of ExoS and ExoT.

Group members

Selected publications

14-3-3 proteins activate Pseudomonas exotoxins-S and -T by chaperoning a hydrophobic surface.
Karlberg T, Hornyak P, Pinto AF, Milanova S, Ebrahimi M, Lindberg M, et al
Nat Commun 2018 09;9(1):3785

Identification of Poly(ADP-Ribose) Polymerase Macrodomain Inhibitors Using an AlphaScreen Protocol.
Ekblad T, Verheugd P, Lindgren AE, Nyman T, Elofsson M, Schüler H
SLAS Discov 2018 04;23(4):353-362

Structural Basis for Potency and Promiscuity in Poly(ADP-ribose) Polymerase (PARP) and Tankyrase Inhibitors.
Thorsell AG, Ekblad T, Karlberg T, Löw M, Pinto AF, Trésaugues L, et al
J. Med. Chem. 2017 02;60(4):1262-1271

Link to more publications


Photo of two men in a lab.
Antonio Ginés García Saura and Herwig Schüler

Mahsa Ebrahimi, Stockholm University

Torun Ekblad, Mabtech, Nacka

Peter Hornyak, Toxintech, Budapest

Tobias Karlberg, Dental and Pharmaceutical Benefits Agency (TLV)

Filipa Pinto, Cytiva (formerly GE Life Sciences)

Taraneh Shirazi, Stockholm University

Ann-Gerd (“Aja”) Thorsell, Sprint Bioscience, Flemingsberg