Location of a ligand recognition site of FMRFamide‐gated Na⁺ channels

Abstract

The second FMRFamide-gated Na + channel (HtFaNaC), from Helisoma trivolvis, has been cloned. HtFaNaC has some different pharmacological properties to HaFaNaC, from Helix aspersa, which has enabled a rational approach to be made to start to identify the FMRFamide recognition site. Several chimeras were made by switching sections between the channels. The differences in sensitivity to FMRFamide, and amiloride, were assessed after expression in Xenopus oocytes. The data suggest that a recognition site for FMRFamide, and the potentiating action of amiloride, resides in a sequence of about 120 amino acids in the extracellular loop proximal to the first transmembrane segment. ß

Endogenous Arginine-Phenylalanine-Amide-related Peptides Alter Steady-state Desensitization of ASIC1a

“…Thus, the APKDL region of ASIC1a likely determines the functional impact of peptide binding rather than peptide binding itself. This idea is supported by the fact that the APKDL residues lie in an area distinct from the proposed peptide-binding site of the related channel FaNaCh (48,51,52). Furthermore, previous data suggest that the peptide-binding site is near a calcium-binding site because calcium attenuates FMRF-amide modulation of ASIC1b/3 heteromultimeric channels (14).…”

Exploration of the Peptide Recognition of an Amiloride-sensitive FMRFamide Peptide-gated Sodium Channel

“…The sequences of HaFaNaC and cASIC1 were retrieved from the GenBank TM (GenBank ID: cASIC1, 63054900, HaFaNaC, 1149511). The alignments of the target sequences were made by Modeler 9.9 and manually adjusted to match published alignments (10 (24,25). Sequence alignments and homology models of protein structures suggest that the regions exhibiting high variation in amino acid sequences participate in the formation of the finger domain (Figs.…”

“…1C and 2A, unconserved residues are highlighted in blue). Assuming that residues 89 -211 contribute to the different FMRFamide affinity between HaFaNaC and HtFaNaC (24,25), we constructed a series of chimeras by substitution of the sequences of HaFaNaC with corresponding sequences on the HtFaNaC, resulting in 13 chimeras, namely chimera 1 (Ch1, Gln-110 -Ile-116, HaFaNaC numbering, similarly hereinafter), chimera 2 (Ch2, Leu-124 -Thr-126), chimera 3 (Ch3, Arg-128 -Tyr-131), chimera 4 (Ch4, Phe-132-Asn-134), chimera 5 (Ch5, Ser-136 -Asn-138), chimera 6 (Ch6, Leu-139 -Thr141), chimera 7 (Ch7, Arg-144 -Arg-150), chimera 8 (Ch8, D154QK), chimera 9 (Ch9, Asn-158 -Ile-160), chimera 10 (Ch10, Gln-169 -Leu-174), chimera 11 (Ch11, Asn-177-Met-183), chimera 12 (Ch12, ) and chimera 13 (Ch13, Ser-198 -Phe-200) ( Fig. 2A).…”

“…For HaFaNaC, the half maximal effective concentration (EC 50 ) of FMRFamide is 2-10 M (17, 24), while for HtFaNaC the value is 70 M (18). The amino acid sequence between residues 89 and 211, located within the extracellular domains of HaFaNaC or HtFaNaC, may be responsible for the different affinities to FMRFamide (24,25), although detailed structural components remain unknown. In addition, alignment of members in the superfamily revealed two specific inserts identified in FaNaC channels (Fig.…”

External Nickel Inhibits Epithelial Sodium Channel by Binding to Histidine Residues within the Extracellular Domains of α and γ Subunits and Reducing Channel Open Probability

“…ASIC are activated by extracellular acidification, and a histidine (His 72 ) in the ECL of ASIC-2a has been identified as a putative H ϩ sensor (111). FaNaCh is a peptide-gated Na ϩ channel, and the peptide (FMRFamide) binding domain was proposed to reside within the ECL (112). Residues or domains within the ECLs of subunits of mechanotransducing channels in Caenorhabditis elegans (i.e.…”