Isatin-induced increase in the affinity of human ferrochelatase and adrenodoxin reductase interaction.

Isatin (indol-2,3-dione) is an endogenous non-peptide regulator exhibiting a wide range of biological and pharmacological activities, which are poorly characterized in terms of their molecular mechanisms. Identification of many isatin-binding proteins in the mammalian brain and liver suggests that isatin may influence their functions. We have hypothesized that besides direct action on particular protein targets, isatin can act as a regulator of protein-protein interactions (PPIs). In this surface plasmon resonance-based biosensor study we have found that physiologically relevant concentrations of isatin (25-100 μM) increase affinity of interactions between human recombinant ferrochelatase (FECH) and NADPH-dependent adrenodoxin reductase (ADR). In the presence of increasing concentrations of isatin the Kd values demonstrated a significant (up to 6-fold) decrease. It is especially important that the interaction of isatin with each individual protein (FECH, ADR) was basically negligible and therefore could not contribute to the observed effect. This effect was specific only for the FECH/ADR complex formation and was not observed for other protein complexes studied: FECH/cytochrome b5(CYB5A) and FECH/SMAD4.