Mortalin Caught in Action: Structures of the Nucleotide Binding Domain in the Apo, ADP‐bound and AMP+PPi‐bound States

Abstract

The heat shock protein 70, Hsp70, chaperone family plays key roles in cellular homeostasis and stress response. Hsp70s not only regulate the folding of nascent proteins, but also prevent aggregation, promote disaggregation, and refold misfolded proteins. The mitochondrial Hsp70, Mortalin, functions in a variety of processes such as mitochondrial protein import and quality control, Fe‐S cluster biogenesis, mitochondrial homeostasis, and regulation of p53, an important tumor suppressor. Mortalin has been implicated in the regulation of apoptosis, cell stress response, neurodegenerative diseases, and has an anti‐apoptotic role in cancer cells. We have elucidated crystal structures of the nucleotide binding domain of human Mortalin in the apo, ADP‐, AMP and AMP states at 2.8 Å, 2.78 Å, and 1.75 Å resolutions, respectively. The crystal structure of Mortalin‐NBD binding to the modified ADP homolog N6propargyl‐ADP has also been determined at 1.49 Å. The overall structures and active site organizations are similar, with a few key differences in side chain positions. Specific residues in the nucleotide binding pocket, which are not conserved in other Hsp70‐family members, lead to lower nucleotide affinity and slower turnover relative to cytosolic Hsp70. ITC and biolayer interferometry experiments performed on the R126W and Y128C disease variants of Mortalin to determine ADP binding and interactions with an inter‐domain linker peptide elucidate how the mutations change Mortalin's functions and how these interactions differ between Mortalin, Hsp70, and Hsc70. ITC experiments have also been performed to test how the MortalinNBD can accommodate modified ADP nucleotides. This structural and binding data may also contribute to the understanding of disease‐associated Mortalin mutations and to improved Mortalin‐targeting antitumor compounds.Support or Funding InformationNSF 15‐52113This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.