Structural and functional analysis of parameters governing tankyrase-1 interaction with telomeric repeat-binding...

Human tankyrase-1 (TNKS) is a member of the poly(ADP-ribose) polymerase (PARP) superfamily of proteins that posttranslationally modify themselves and target proteins with ADP-ribose (termed PARylation). The TNKS ankyrin repeat domain mediates interactions with a growing number of structurally and functionally diverse binding partners, linking TNKS activity to multiple critical cell processes, including Wnt signaling, Golgi trafficking, and telomere maintenance. However, some binding partners can engage TNKS without being modified, suggesting that separate parameters influence TNKS interaction and PARylation. Here, we present an analysis of the sequence and structural features governing TNKS interactions with two model binding partners: the PARylated partner telomeric repeat-binding factor 1 (TRF1) and the non-PARylated partner GDP-mannose 4,6-dehydratase (GMD). Using a combination of TNKS-binding assays, PARP activity assays, and analytical ultracentrifugation sedimentation analysis, we found that both the specific sequence of a given TNKS-binding peptide motif and the quaternary structure of individual binding partners play important roles in TNKS interactions. We demonstrate that GMD forms stable 1:1 complexes with the TNKS ankyrin repeat domain; yet, consistent with results from previous studies, we were unable to detect GMD modification. We also report in vitro evidence that TNKS primarily directs PAR modification to glutamate/aspartate residues. Our results suggest that TNKS-binding partners possess unique sequence and structural features that control binding and PARylation. Ultimately, our findings highlight the binding partner:ankyrin repeat domain interface as a viable target for inhibition of TNKS activity.