Spectroscopic and QM/MM studies of the Cu(I) binding site of the plant ethylene receptor ETR1

Models for the Structure and Function of the Ethylene Receptor

“…A recent study performed extensive modeling of the transmembrane domain of ETR1. 20 The binding of copper to the protein was also examined experimentally, which was the source of the implied stoichiometry of one copper ion per ETR1 chain mentioned above. Molecular dynamics examined the binding of ethylene to the receptor, but at the macromolecular level, such simulations do not reveal the molecular detail addressed in the small molecule crystal structures studied here.…”

“…36 The expected but unneeded complexity of a structure involving one norbornadiene bound to two copper centers dissuaded us from efforts to crystallize this complex. Encouraged by the ability to form a copper complex with a strained alkene and one of our ligands when we had been unable to do so with ethylene, we examined two strained alkenes that can bind only one copper, norbornene (20) and trans-cyclooctene (21).…”

Biological formation of ethylene

“…1A). 8 Plants sense the levels of ethylene in their environment using a copper-containing sensor protein, 9,10 resulting in fruit ripening and other effects.…”

Basis for high-affinity ethylene binding by the ethylene receptor ETR1 of Arabidopsis

“…Due in part to the difficulty in obtaining high-resolution structural information from TM domains, much of what is known about the requirements for ethylene binding by the receptors comes from a coupling of biochemical and genetic analyses ( 5 , 7 , 20 , 22 , 23 ). Through these analyses, the receptors have been determined to function as homodimers, with ethylene binding mediated through an associated Cu(I) co-factor ( 7 , 22 – 25 ). A set of highly conserved Cys and His residues in the TM domain is implicated in chelating the copper cofactor ( 5 , 7 , 25 ).…”

“…Through these analyses, the receptors have been determined to function as homodimers, with ethylene binding mediated through an associated Cu(I) co-factor ( 7 , 22 – 25 ). A set of highly conserved Cys and His residues in the TM domain is implicated in chelating the copper cofactor ( 5 , 7 , 25 ). Initial analysis indicated the existence of one copper cofactor per receptor dimer, suggesting a model in which the copper is chelated by two Cys and two His residues, thereby resulting in a single ethylene-binding site per receptor dimer ( 7 ).…”