Specific cellular labeling of a clinically important estrogen receptor alpha mutant, Y537S, with an affimer

Mutations in estrogen receptor alpha (ERα), a nuclear transcription factor, are associated with metastasis and poor disease-free survival of breast cancers patients. We isolated and characterized the specificity of a new ∼13kD Affimer selected for binding to Y537S mutant with estradiol and compared its binding against wild-type ERα, L536S (a negative control), and D538G (a weakly constituently active mutant), with and without 17β-estradiol (E2) and two selective estrogen receptor modulators (SERMs), 4-hydroxytamoxifen (4OHT) and 27-hydroxycholesterol (27HC).