Sigma Proteins: Evolution of the Concept of Sigma Receptors

Two sigma receptor subtypes have been proposed, sigma1 and 2. Much of our understanding of this system is based on biochemical and pharmacological characterization of the cloned sigma1 receptor subtype (Sigma1). It has become clear that sigma receptors are not canonical receptors. Sigma1 is highly conserved among mammalian species, however, it does not share significant homology with any other mam...