The HDQVH-motif in domain E of the estradiol receptor alpha is responsiblefor zinc-binding and zinc-induced hormone release

The estradiol receptor cc and proteolytic fragments thereof which contain t he entire ligand-binding domain E, bind Zn-65 with high affinity. Four puta tive double-histidine zinc-binding sequences can be identified within the h ormone-binding domain E: HDQVH [amino acid (aa) 373-377; ], HIH (aa 474-476 ), HFRH (aa 513-516) and HRLH (aa 547-550). Only the HDQVH-motif is respons ible for the 1:I zinc-binding to domain E because the proteolytic (endo-Lys -C) 17 kDa fragment (aa 303-467) from porcine estradiol receptor cl possess es the zinc-binding ability but none of the fragments containing the other motifs. In addition, H373A- and H377A-mutants lack the metal-binding capaci ty. Moreover, divalent metal ions are able to release estradiol out of the binding-niche. The order for this feature parallels the competition pattern of Zn-65-binding: Mg2+ < Ni2+ much less than Zn2+ less than or equal to Cu 2+. Mutant estradiol receptor cl fragments (H373A and H377A) lack the zinc- induced hormone release. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.