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1.A.6.3.2
FMRFamide (peptide)-gated  sodium channel, FaNaC.  The charge on aspartate-552 in TMS2 influcences the gating properties and potency of the channel (Kodani and Furukawa 2010; Kodani and Furukawa 2014).  The FMRFamide-evoked current through AkFaNaC was depressed 2-3-fold by millimolar (1.8 mM) Ca2+ (Fujimoto et al. 2017). Both D552 and D556 were indispensable for the sensitivity of FaNaC to millimolar Ca2+. The Ca2+-sensitive gating was recapitulated by an allosteric model in which Ca2+-bound channels are more difficult to open. The desensitization of FaNaC was also inhibited by Ca2+ (Fujimoto et al. 2017).  High-resolution cryo-EM structures of FaNaC in both apo and FMRFamide-bound states have been solved (Liu et al. 2023). AcFaNaC forms a chalice-shaped trimer and possesses several notable features, including two FaNaC-specific insertion regions, a distinct finger domain and non-domain-swapped TMS2 in the transmembrane domain (TMD). One FMRFamide binds to each subunit in a cleft located in the top-most region of the extracellular domain, with participation of residues from the neighboring subunit. Bound FMRFamide hass an extended conformation. FMRFamide binds tightly to A. californica FaNaC in an N terminus-in manner, which causes collapse of the binding cleft and induces large local conformational rearrangements. Such conformational changes are propagated downward toward the TMD via the palm domain, possibly resulting in outward movement of the TMD and dilation of the ion conduction pore (Liu et al. 2023).

Accession Number:Q4H3X6
Protein Name:FMRFamide-gated Na+ channel
Length:653
Molecular Weight:73978.00
Species:Aplysia kurodai (Kuroda's sea hare) [6501]
Number of TMSs:2
Substrate sodium(1+)

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FASTA formatted sequence
1:	MLGRGERIKP YHFRDSSADH MKYTSVAAKS GMVPEHRYTM VRSRHHGRHH HHHSYQEYNT 
61:	QRSAISLIAE LGSESNAHGL AKIVTSRDTK RKVIWALMVI IGFTAATLQL SLLVRKYLQF 
121:	QVVELSEIKD SMPVEYPSVT ICNIEPISLR KIRKAYNKNE SQNLKDWLNF TQTFHFKDMS 
181:	FMNSIRAFYE NLGTDAKKIS HDLRDLLIHC RFNREECTTE NFTSSFDGNY FNCFTFNGGQ 
241:	LRDQLQMHAT GPENGLSLII SIEKDEPLPG TYGVYNFENN ILHSAGVRVV VHAPGSMPSP 
301:	VDHGFDIPPG YSSSVGLKAL LHTRLSEPYG NCTEDSLEGI QTYRNTFFAC LQLCKQRRLI 
361:	RECKCKSSAL PDLSVENITF CGVIPDWKDI RRNVTGEYKM NQTIPTISLA CEARVQKQLN 
421:	NDRSYETDCG CYQPCSETSY LKSVSLSYWP LEFYQLSALE RFFSQKHPTD QQHFMKIAQD 
481:	FLSRLAHPQQ QALARNNSHD KDILTTSYSL SEKEMAKEAS DLIRQNLLRL NIYLEDLSVV 
541:	EYRQLPAYGL ADLFADIGGT LGLWMGISVL TIMELMELII RLFALIFNAE REVPKAPMHN 
601:	SNNGGSGGGD GSGGQHNFAN GDVEHERDTH FPDLGSSDFD FRRGGGIGAE SPV