Kelch-like ECH-associated protein 1 is a protein that in humans is encoded by the Keap1 gene. Keap1 has four discrete protein domains. The N-terminal Broad complex, Tramtrack and Bric-à-Brac (BTB) domain contains the Cys151 residue, which is one of the important cysteines in stress sensing. The intervening region (IVR) domain contains two critical cysteine residues, Cys273 and Cys288, which are a second group of cysteines important for stress sensing. A double glycine repeat (DGR) and C-terminal region (CTR) domains collaborate to form a β-propeller structure, which is where Keap1 interacts with Nrf2. Mutations in KEAP1 that result in loss-of-function are not linked to familial cancers, though they do predispose individuals to multinodular goiters. The proposed mechanism leading to goiter formation is that the redox stress experienced when the thyroid produces hormones selects for loss of heterozygosity of KEAP1, leading to the goiters.