Three pairs of cysteine residues mediate both redox and Zn2+ modulation ofthe NMDA receptor

NMDA receptor activity is modulated by various compounds, including sulfhyd ryl redox agents and Zn2+. In addition to a slow and persistent component o f redox modulation common to all NMDA receptors, NR1/NR2A receptors uniquel y have a rapid and reversible component that has been variously attributed to redox or Zn2+ effects. Here we show that this rapid modulatory effect ca n be described by two time constants with relatively fast (similar to6 sec) and intermediate (60 sec) half lives, and it is likely to be attributable to both redox agents and Zn2+. Using site-directed mutagenesis, we identifi ed three pairs of cysteine residues that underlie the various kinetic compo nents of redox modulation of NMDA-evoked currents in Xenopus oocytes expres sing NR1/NR2A receptors: (1) Cys 87 and Cys 320 in NR2A underlie the fast c omponent, (2) Cys 79 and Cys 308 in NR1 underlie the intermediate component , and (3) Cys 744 and Cys 798 in NR1 underlie the persistent component. Mut ation of these redox-sensitive cysteine residues also affects high-affinity , voltage-independent Zn2+ inhibition that is specific to NR1/NR2A receptor s. Exposure to methanethiosulfonate agents that modify cysteine residues di d not block the Zn2+ inhibition. Thus, these cysteine residues do not appea r to coordinate Zn2+ directly. Instead, the redox status of these cysteine residues may modulate the sensitivity of the receptor to Zn2+.