ct0c00249_si_001.pdf (1.17 MB)
Mechanism of Fully Reversible, pH-Sensitive Inhibition of Human Glutamine Synthetase by Tyrosine Nitration
journal contribution
posted on 2020-07-03, 18:03 authored by Benedikt Frieg, Boris Görg, Natalia Qvartskhava, Thomas Jeitner, Nadine Homeyer, Dieter Häussinger, Holger GohlkeGlutamine
synthetase (GS) catalyzes an ATP-dependent condensation
of glutamate and ammonia to form glutamine. This reactionand
therefore GSare indispensable for the hepatic nitrogen metabolism.
Nitration of tyrosine 336 (Y336) inhibits human GS activity. GS nitration
and the consequent loss of GS function are associated with a broad
range of neurological diseases. The mechanism by which Y336 nitration
inhibits GS, however, is not understood. Here, we show by means of
unbiased MD simulations, binding, and configurational free energy
computations that Y336 nitration hampers ATP binding but only in the
deprotonated and negatively charged state of residue 336. By contrast,
for the protonated and neutral state, our computations indicate an
increased binding affinity for ATP. pKa computations of nitrated Y336 within GS predict a pKa of ∼5.3. Thus, at physiological pH, nitrated
Y336 exists almost exclusively in the deprotonated and negatively
charged state. In vitro experiments confirm these
predictions, in that, the catalytic activity of nitrated GS is decreased
at pH 7 and 6 but not at pH 4. These results indicate a novel, fully
reversible, pH-sensitive mechanism for the regulation of GS activity
by tyrosine nitration.