Soluble and membrane-bound protein carrier mediate direct copper transport to the ethylene receptor family

Abstract

The plant hormone ethylene is a key regulator of plant growth, development and stress adaption. Ethylene perception and response are mediated by a family of integral membrane receptors (ETRs) localized at the ER-Golgi network. The biological function of these receptors relies on a protein-bound copper cofactor. Nonetheless, molecular processes and structures controlling assembly and integration of the metal into the functional plant hormone receptor are still unknown. Here, we have explored the molecular pathways of copper transfer from the plant cytosol to the ethylene receptor family by analyzing protein–protein interactions of receptors with soluble and membrane-bound plant copper carriers. Our results suggest that receptors primarily acquire their metal cofactor from copper transporter RESPONSIVE-TO-ANTAGONIST-1 (RAN1) which has been loaded with the transition metal beforehand by soluble copper carriers of the ATX1-family. In addition, we found evidence for a direct interaction of ETRs with soluble chaperones ANTIOXIDANT-1 (ATX1) and COPPER TRANSPORT PROTEIN (CCH) raising the possibility of a direct copper exchange between soluble chaperones and receptors.

Comparative study of the effects of selenium yeast and sodium selenite on selenium content and nutrient quality in broccoli florets (Brassica oleracea L. var. italica)

“…Effects on the content of soluble protein and soluble sugar Soluble protein and soluble sugar are important osmotic adjustment substances in plant cells and play vital roles in the nutrient quality of vegetables. 26,27 In the present study, all Se treatments reduced the soluble protein content in broccoli florets compared to that in the non-selenized treatment group (Fig. 3A).…”

Ethylene signaling in plants

“…Mutants such as this render the plant ethylene insensitive. Additionally, several studies have determined that the ER membrane-localized copper transporter, responsive to antagonist1 (RAN1), physically interacts with at least some of the receptors and is needed for delivery of copper and proper biogenesis of the ethylene receptors (74)(75)(76)(77)(78). Because copper co-purifies with the ETR1 dimer with a 1:1 stoichiometry, it was long thought that each receptor dimer contains one copper ion (21).…”

“…Specific proteins have been identified as interacting partners with all or a subset of the ethylene receptors. This includes interactions with RAN1 which may be important for correct delivery of copper to the receptors (78). Other interacting partners are less characterized.…”

Mapping the helix arrangement of the reconstituted ETR1 ethylene receptor transmembrane domain by EPR spectroscopy

“…Copper(I) is an essential cofactor to mediate high-affinity ethylene binding 33,34 and was included in the in silico model, 12 but absent in our experiments so far. In the eld of ethylene receptors there are still open questions regarding transfer routes and coordination of copper(I).…”