Nitration-driven structural changes in Hsp90 linked to gain of pathological functions.

Protein tyrosine (Y) nitration is an oxidative modification that occurs in pathological conditions such as neurodegenerative diseases and solid tumors. Depending on the location of the tyrosine residue, nitration can modify protein structure and function and affect cellular processes. We previously showed that site-specific nitration of the molecular chaperone heat shock protein 90 (Hsp90) leads to distinct pathological gain-of-function that cannot be compensated or overcome by native Hsp90. While Hsp90 nitrated on Y33 localizes in mitochondria and decreases mitochondrial metabolism, Hsp90 nitrated on Y56 activates the purinergic receptor and calcium channel P2X7, triggering downstream signaling pathways that can lead to either cell proliferation or apoptosis, depending on the cell type. Herein, using complementary biophysical, biochemical, and in silico methods, we show that nitration on Y33 and Y56 triggers significant site-dependent local and global structural changes linked to changes in Hsp90 activity. Nitration of these critical residues led to destabilization of Hsp90 dimer and formation of stable oligomeric species, with differential effects on Hsp90 ATPase and chaperone holdase activities depending on the nitrated residue. Molecular dynamics simulations further support the impact of nitration on Y33 and Y56 on the ATP-lid dynamics and the interaction of ATP with R392, critical to Hsp90 ATPase activity. Establishing the molecular basis of nitration-induced structural changes in Hsp90 leading to disease-driving functions is the first step toward the development of therapeutic approaches selectively targeting these pathological variants of Hsp90.