Probing the Structural Basis of Zn2+ Regulation of the Epithelial Na+ Channel

Abstract

Background: Extracellular Zn 2ϩ regulates epithelial Na ϩ channel (ENaC) activity.

Deletion of α-subunit exon 11 of the epithelial Na+ channel reveals a regulatory module

“…The knuckle domain of the ␣-subunit borders the finger domain of the ␥-subunit (14,18,22,26,29,30). There are a number of sites in the ␥-subunit finger domain that have roles in modulating the channel's response to extracellular factors, including Na ϩ , Zn 2ϩ , and proteases (6,15,24,41,47,56). Based on these findings, we speculate that interactions at the interface between the ␣-subunit knuckle domain and ␥-subunit finger domain may have an important role in the allosteric regulation of ENaC P o by external factors.…”

Gain-of-function variant of the human epithelial sodium channel

“…A large conformational change of these two loops was revealed by comparing resolved desensitized ASIC1 structures and conductive, psalmotoxin bound ASIC1 structures (3). We recently identified two residues within the loops connecting the ␤ 1 -␤ 2 -and ␤ 11 -␤ 12 -strands of mouse ␥ENaC (␥H88 and ␥D516) as determinants of a low affinity inhibitory Zn 2ϩ binding site (13). In this study, we identified a nonsynonymous variant (␥L511Q, reference sequence ID: rs113234492) that is located within the ␤ 11 -␤ 12 -loop of the human ␥ENaC subunit.…”

“…7C). Residues within this linker region as well as the ␤ 1 -␤ 2 -linker region have been implicated in the regulation of ASIC and ENaC gating, including two residues (mouse ␥H88 and ␥D516) that have a role in the regulation of ENaC gating by Zn 2ϩ (13,27,42). Comparisons of resolved psalmotoxinbound ASIC1a structures with a desensitized ASIC1a structure (18) revealed large structural rearrangements of the residues linking the ␤ 11 -␤ 12 -and ␤ 1 -␤ 2 -strands in the palm domain (3).…”

Zinc as Allosteric Ion Channel Modulator: Ionotropic Receptors as Metalloproteins

“…αβγ heteromers are zinc-sensitive, with increased currents and abolishment of the sodium auto-inhibition with 100 mM extracellular sodium. The positive modulator effect of the metal was observed with EC 50 s of 1.7 [ 106 ] or 2.1 µM [ 24 ] and voltage-independence [ 106 ]. However, with 1000-fold more zinc, the effect was inverted, exhibiting a negative modulation [ 107 ] with IC 50 of 2.1 mM zinc [ 24 ].…”

“…Low zinc concentrations exhibit a positive modulator effect while higher metal concentrations elicit a negative modulation. The structural basis of this dichotomy has shown that H88 in the γ subunit abolished the inhibitory effect of zinc, while H193, H200 and H202 are involved in the positive allosteric modulator role of the metal activity in adjacent receptor subdomains [ 24 ].…”