Abstract Polymerase δ-interacting protein 2 (POLDIP2, PDIP38) is a multifaceted, ‘moonlighting’ protein, involved in binding protein partners from many different cellular processes, including mitochondrial metabolism, DNA replication and repair, and reactive oxygen species generation. POLDIP2 is found in multiple cellular compartments, potentially shuttled depending on its role. How POLDIP2 binds to and coordinates many different proteins is currently unknown. Towards this goal, we present the crystal structure of the ‘mitochondrial’ fragment of POLDIP2 to 2.8 Å. POLDIP2 exhibited a compact two-domain β-strand-rich globular structure, confirmed by circular dichroism and small angle X-ray scattering approaches. POLDIP2 comprised canonical DUF525 (ApaG) and YccV-like domains, but with the conserved domain linker packed tightly, resulting in an ‘extended’ YccV module. A central channel through POLDIP2 was observed which we hypothesise could influence structural changes potentially mediated by redox conditions, following observation of a modified cysteine residue in the channel. Unstructured regions were rebuilt by ab initio modelling to generate a model of full length POLDIP2. Molecular dynamics simulations revealed a highly dynamic N-terminal region tethered to the YccV-domain by an extended linker, potentially facilitating interactions with distal binding partners. Finally we build models of POLDIP2 interacting in complex with two of its partners in genome stability, PrimPol and PCNA. These indicate that dynamic flexibility of the POLDIP2 N-terminal and loop regions are critical to mediate protein-protein interactions.

Crystal structure and molecular dynamics of human POLDIP2, a multifaceted adaptor protein in metabolism and genome stability