Structural insights into SAM domain‐mediated tankyrase oligomerization

Abstract

Tankyrase 1 (TNKS1; a.k.a. ARTD5) and tankyrase 2 (TNKS2; a.k.a ARTD6) are highly homologous poly(ADP-ribose) polymerases (PARPs) that function in a wide variety of cellular processes including Wnt signaling, Src signaling, Akt signaling, Glut4 vesicle translocation, telomere length regulation, and centriole and spindle pole maturation. Tankyrase proteins include a sterile alpha motif (SAM) domain that undergoes oligomerization in vitro and in vivo. However, the SAM domains of TNKS1 and TNKS2 have not been structurally characterized and the mode of oligomerization is not yet defined. Here we model the SAM domain-mediated oligomerization of tankyrase. The structural model, supported by mutagenesis and NMR analysis, demonstrates a helical, homotypic head-to-tail polymer that facilitates TNKS self-association. Furthermore, we show that TNKS1 and TNKS2 can form (TNKS1 SAM-TNKS2 SAM) hetero-oligomeric structures mediated by their SAM domains. Though wild-type tankyrase proteins have very low solubility, model-based mutations of the SAM oligomerization interface residues allowed us to obtain soluble TNKS proteins. These structural insights will be invaluable for the functional and biophysical characterization of TNKS1/2, including the role of TNKS oligomerization in protein poly(ADP-ribosyl)ation (PARylation) and PARylation-dependent ubiquitylation.

Regulation of Wnt/β‐catenin signalling by tankyrase‐dependent poly(ADP‐ribosyl)ation and scaffolding

“…Both TNKS and TNKS2 polymerize through their SAM domains (De Rycker and Price, ; Mariotti et al, ; Riccio et al, ). Recent crystallographic studies of the SAM domains revealed the primarily electrostatic nature of the head‐to‐tail SAM–SAM interfaces within the helical filament (Mariotti et al, ; Riccio et al, ) (Figure F), in agreement with a polymer model guided by NMR studies to identify the residues perturbed upon polymerization (DaRosa et al, ). Compatible with the outward‐facing N‐ and C‐termini in the filament (DaRosa et al, ; Mariotti et al, ; Riccio et al, ), full‐length tankyrase indeed polymerizes (De Rycker and Price, ; Mariotti et al, ; Riccio et al, ).…”

“…Recent crystallographic studies of the SAM domains revealed the primarily electrostatic nature of the head‐to‐tail SAM–SAM interfaces within the helical filament (Mariotti et al, ; Riccio et al, ) (Figure F), in agreement with a polymer model guided by NMR studies to identify the residues perturbed upon polymerization (DaRosa et al, ). Compatible with the outward‐facing N‐ and C‐termini in the filament (DaRosa et al, ; Mariotti et al, ; Riccio et al, ), full‐length tankyrase indeed polymerizes (De Rycker and Price, ; Mariotti et al, ; Riccio et al, ). TNKS and TNKS2 form cytoplasmic puncta rather than microscopically visible filaments, which may reflect the dynamic nature of the polymers (Mariotti et al, ; Riccio et al, ).…”

“…Furthermore, additional tankyrase interactors in the Wnt/β‐catenin pathway, other than AXIN, are emerging (Croy et al, ). Structure–function studies are providing a detailed picture of the molecular mechanisms by which tankyrase controls Wnt/β‐catenin signalling and are revealing non‐catalytic scaffolding roles of tankyrase (Guettler et al, ; Morrone et al, ; DaRosa et al, , ; Eisemann et al, ; Mariotti et al, ; Riccio et al, ; Xu et al, ). Conserved functions of tankyrase in the Wnt/β‐catenin pathway are being increasingly appreciated from studies in Drosophila and human CRC cell lines (Lau et al, ; de la Roche et al, ; Yang et al, ; Wang et al, , ).…”

Structural basis for tankyrase‐RNF146 interaction reveals noncanonical tankyrase‐binding motifs

“…(A)]. Immediately upstream of this catalytic domain lies a SAM domain responsible for TNKSs polymerization . The extreme N‐terminal end harbors a histidine, serine, proline‐rich segment (a region lacking in tankyrase‐2), followed by a large ankyrin repeat domain composed of five conserved subdomains or ankyrin repeat clusters (ARCs) connected by conserved linkers.…”

“…Immediately upstream of this catalytic domain lies a SAM domain responsible for TNKSs polymerization. [21][22][23][24][25][26] The extreme Nterminal end harbors a histidine, serine, proline-rich segment (a region lacking in tankyrase-2), followed by a large ankyrin repeat domain composed of five conserved subdomains or ankyrin repeat clusters (ARCs) connected by conserved linkers. With the exception of ARC3, each ARC has a highly conserved binding groove that can recognize a tankyrasebinding motif (TBM) having the form: RXXUDG where X is any amino acid, and U is a small hydrophobic amino acid (Supporting Information Fig.…”