Undetectable Intracellular Free Copper: The Requirement of a Copper Chaperone for Superoxide Dismutase

Abstract

The copper chaperone for the superoxide dismutase (CCS) gene is necessary for expression of an active, copper-bound form of superoxide dismutase (SOD1) in vivo in spite of the high affinity of SOD1 for copper (dissociation constant = 6 fM) and the high intracellular concentrations of both SOD1 (10 microM in yeast) and copper (70 microM in yeast). In vitro studies demonstrated that purified Cu(I)-yCCS protein is sufficient for direct copper activation of apo-ySOD1 but is necessary only when the concentration of free copper ions ([Cu]free) is strictly limited. Moreover, the physiological requirement for yCCS in vivo was readily bypassed by elevated copper concentrations and abrogation of intracellular copper-scavenging systems such as the metallothioneins. This metallochaperone protein activates the target enzyme through direct insertion of the copper cofactor and apparently functions to protect the metal ion from binding to intracellular copper scavengers. These results indicate that intracellular [Cu]free is limited to less than one free copper ion per cell and suggest that a pool of free copper ions is not used in physiological activation of metalloenzymes.

Formation constants of copper(i) complexes with cysteine, penicillamine and glutathione: implications for copper speciation in the human eye

“…It should be noted that due to E h = 223 mV selected in the present model for 'lens water', the free Cu + concentration (1.2  10 13 M) is significantly higher than that of Cu 2+ (10 19 M, see above). In contrast, Rae et al 76 estimated much lower free Cu + concentrations for cytoplasm (< 10 23 M vs. < 10 18 M for Cu 2+ ), which appears to be inconsistent with the strongly reducing conditions maintained in cells.…”

“…For 'lens water', a significantly lower free Cu 2+ concentration of 10 -19 M was selected to simulate the strong bonding to proteins and enzymes, 76 which occur in the lens and cornea in high concentrations as part of the oxidative stress defence system. The results (Table 8) indicate a free Cu + concentration lower than in AH but a higher total Cu + concentration.…”

XIAP: Cell death regulation meets copper homeostasis

“…However, free copper is very toxic due to its ability to react with hydrogen peroxide and generate highly reactive hydroxyl radicals. Consequently, free copper in the cell is almost undetectable and complex homeostatic mechanisms have evolved to regulate intracellular copper distribution and excretion [36].…”

Les bases moléculaires de l’approvisionnement en cuivre

“…Chez S. cerevisiae, il a été démontré que chaque cellule compte moins d'un ion de cuivre libre [10]. En raison de cette rareté, le cuivre intracellulaire est associé à différentes protéines qui le distribuent et l'utilisent ( Figure 2).…”

“…En raison de cette rareté, le cuivre intracellulaire est associé à différentes protéines qui le distribuent et l'utilisent ( Figure 2). Trois protéines chaperonnes spécifiques pour chacune de leur cible permettent la distribution du cuivre : Ccs1 [10], Cox17 [11] et Atx1 [12].…”