ZN+2 INDUCES REVERSIBLE CROSS-LINKING OF HUMAN PLACENTAL THYROID-HORMONE NUCLEAR RECEPTOR WITH NO EFFECT ON HORMONE BINDING

Zn+2 is required for specific binding of c-erbA proteins to the hormone response elements of target genes. It is unclear whether Zn+2 is important for the binding of ligand to c-erbA proteins. The present study evaluated the effect of Zn+2 and other divalent cations on the binding of 3,3′,5-triiodo-L-thyronine(T3) to the purified human placental c-erbA protein (h-TRβ1). Zn+2 induced cross-linking of h-TRβ1 to form aggregates in a dose-dependent manner with an apparent half-maximal concentration of ∼ 200 μM at 22°C. Cross-linking was reversible by the addition of 5 μM EDTA or 10 mM dithiothreitol. The cross-linked h-TRβ1 bound T3. These results indicated Zn+2 had no effect on T3 binding and suggested that the cysteines and histidines involved in crosslinking are not essential for T3 binding. © 1991 Academic Press, Inc.