Cysteine-based regulation of the CUL3 adaptor protein Keap1

Nrf2 (NF-E2-related factor 2) is a master transcription factor containing a powerful acidic transcriptional activation domain. Nrf2-dependent gene expression impacts cancer chemoprevention strategies, inflammatory responses, and progression of neurodegenerative diseases. Under basal conditions, association of Nrf2 with the CUL3 adaptor protein Keap1 results in the rapid Nrf2 ubiquitylation and proteasome-dependent degradation. Inhibition of Keap1 function blocks ubiquitylation of Nrf2, allowing newly synthesized Nrf2 to translocate into the nucleus, bind to ARE sites and direct target gene expression. Site-directed mutagenesis experiments coupled with proteomic analysis support a model in which Keap1 contains at least 2 distinct cysteine motifs. The first is located at Cys 151 in the BTB domain. The second is located in the intervening domain and centers around Cys 273 and 288. Adduction or oxidation at Cys151 has been shown to produce a conformational change in Keap1 that results in dissociation of Keap1 from CUL3, thereby inhibiting Nrf2 ubiquitylation. Thus, adduction captures specific chemical information and translates it into biochemical information via changes in structural conformation.