Figure 7.

Model of Ethylene Binding Site(A) Copper loading of ethylene receptors by RAN1. RAN1 is a copper transporting ATPase. Copper is bound to RAN1 by two aminoterminal metal-binding motifs and then transported across the membrane. Copper is delivered to the ethylene receptor apoproteins. One copper ion is coordinated per receptor homo-dimer. Upon coordinating copper, the ethylene receptors are competent for ethylene binding.(B) Transmembrane structure of ethylene binding site. There is one copper binding site and consequently one ethylene-binding site per receptor homodimer. Each monomer of the receptor homodimer contains three transmembrane segments. Cys65 and His69 coordinate the copper ion within the second transmembrane domains of each monomer.