9E4I: Human ASIC1a at pH 7.5

Human ASIC1a at pH 7.5 in complex with MitTx. Determined by electron microscopy at 2.33 Å resolution. Released 21 Jan 2026.

Method: Electron microscopy
Resolution: 2.33 Å
Organisms: Homo sapiens, Micrurus tener tener
Chains: 9
Atoms: 14,241
Mol. weight: 243.41 kDa
Released: 21 Jan 2026

Explore 9E4I in 3D Show helices and sheets RCSB PDB PDBe

Secondary structure: helices and β-sheets

9E4I contains 116 α-helices and 90 β-strands across 9 chains. Residue ranges use author residue numbering, as in the PDB file, from PDBe. To see them in 3D, choose the Cartoon representation with Secondary structure coloring: helices, sheets and coils get different colors.

Chain A: 27 helices, 22 β-strands

Element	Residues	Length	Sheet
α-helix	41-68	28
β-strand	73-80	8	1
β-strand	85-86	2	2
α-helix	87-88	2
β-strand	89-94	6	3
β-strand	99	1	4
α-helix	105-111	7
α-helix	127-129	3
α-helix	132-141	10
α-helix	154-161	8
α-helix	163-164	2
α-helix	165-168	4
β-strand	169-174	6	1
β-strand	177-178	2	1
α-helix	181-183	3
β-strand	184-189	6	3
β-strand	192-197	6	3
α-helix	200-202	3
α-helix	205-207	3
β-strand	208-209	2	2
α-helix	214-216	3
β-strand	218-223	6	1
α-helix	226-228	3
β-strand	229	1	4
α-helix	230-232	3
β-strand	243	1	5
β-strand	245-250	6	3
α-helix	258-261	4
β-strand	263-265	3	3
β-strand	269-281	13	1
α-helix	283-284	2
β-strand	291	1	6
α-helix	307-323	17
β-strand	326	1	7
α-helix	335	1
β-strand	336	1	7
α-helix	337-338	2
α-helix	339-341	3
α-helix	342-346	5
α-helix	347-351	5
α-helix	352-356	5
α-helix	363-365	3
β-strand	366	1	6
β-strand	368-380	13	1
α-helix	387-393	7
α-helix	398-404	7
β-strand	405-412	8	1
β-strand	417-424	8	1
α-helix	428-450	23

Chain B: 29 helices, 22 β-strands

Element	Residues	Length	Sheet
α-helix	42-69	28
β-strand	73-80	8	5
β-strand	85-86	2	8
α-helix	87-88	2
β-strand	89-94	6	9
β-strand	99	1	10
α-helix	100-102	3
α-helix	105-111	7
α-helix	132-141	10
α-helix	149-151	3
α-helix	154-161	8
α-helix	163-164	2
α-helix	165-168	4
β-strand	169-174	6	5
β-strand	177-178	2	5
α-helix	181-183	3
β-strand	184-189	6	9
β-strand	192-197	6	9
α-helix	200-202	3
α-helix	205-207	3
β-strand	208-209	2	8
α-helix	214-216	3
β-strand	218-223	6	5
α-helix	226-228	3
β-strand	229	1	10
α-helix	230-231	2
β-strand	243	1	11
β-strand	245-250	6	9
α-helix	258-261	4
β-strand	263-265	3	9
β-strand	269-281	13	5
α-helix	283-284	2
β-strand	291	1	12
α-helix	307-323	17
β-strand	326	1	13
α-helix	335	1
β-strand	336	1	13
α-helix	337-338	2
α-helix	339-341	3
α-helix	342-346	5
α-helix	347-351	5
α-helix	352-356	5
α-helix	363-365	3
β-strand	366	1	12
β-strand	368-380	13	5
α-helix	387-393	7
α-helix	398-404	7
β-strand	405-412	8	5
β-strand	417-424	8	5
α-helix	428-446	19
α-helix	448-451	4

Chain C: 27 helices, 22 β-strands

Element	Residues	Length	Sheet
α-helix	43-69	27
β-strand	73-80	8	11
β-strand	85-86	2	14
α-helix	87-88	2
β-strand	89-94	6	15
β-strand	99	1	16
α-helix	105-111	7
α-helix	127-129	3
α-helix	132-141	10
α-helix	154-161	8
α-helix	163-164	2
α-helix	165-168	4
β-strand	169-174	6	11
β-strand	177-178	2	11
α-helix	181-183	3
β-strand	184-189	6	15
β-strand	192-197	6	15
α-helix	200-202	3
α-helix	204-207	4
β-strand	208-209	2	14
α-helix	214-216	3
β-strand	218-223	6	11
α-helix	226-228	3
β-strand	229	1	16
α-helix	230-231	2
β-strand	243	1	1
β-strand	245-250	6	15
α-helix	258-261	4
β-strand	263-265	3	15
β-strand	269-281	13	11
α-helix	283-284	2
β-strand	291	1	17
α-helix	307-323	17
β-strand	326	1	18
α-helix	335	1
β-strand	336	1	18
α-helix	337-338	2
α-helix	339-341	3
α-helix	342-346	5
α-helix	347-351	5
α-helix	352-356	5
α-helix	363-365	3
β-strand	366	1	17
β-strand	368-380	13	11
α-helix	387-393	7
α-helix	398-404	7
β-strand	405-412	8	11
β-strand	417-424	8	11
α-helix	428-450	23

Chain D: 4 helices, 3 β-strands

Element	Residues	Length	Sheet
α-helix	5-8	4
α-helix	10-11	2
β-strand	21-27	7	19
β-strand	32-38	7	19
β-strand	48	1	19
α-helix	51-54	4
α-helix	55-59	5

Chains E and I: 8 helices, 5 β-strands

Element	Residues	Length	Sheet
α-helix	2-12	11
α-helix	17-20	4
β-strand	23	1	20
β-strand	27	1	20
α-helix	38-52	15
α-helix	53-57	5
β-strand	69	1	21
α-helix	74-76	3
β-strand	78	1	21
α-helix	85-103	19
α-helix	108-110	3
β-strand	111	1	20
α-helix	115-117	3

Chains F and H: 3 helices, 3 β-strands

Element	Residues	Length	Sheet
α-helix	5-8	4
α-helix	10-11	2
β-strand	21-27	7	22
β-strand	32-38	7	22
β-strand	48	1	22
α-helix	51-58	8

Chain G: 7 helices, 5 β-strands

Element	Residues	Length	Sheet
α-helix	2-12	11
α-helix	17-20	4
β-strand	23	1	23
β-strand	27	1	23
α-helix	38-55	18
β-strand	69	1	24
α-helix	74-76	3
β-strand	78	1	24
α-helix	85-103	19
α-helix	108-110	3
β-strand	111	1	23
α-helix	115-117	3

Molecules and chains

Molecule	Chains	Type	Length	Organism	UniProt
Acid-sensing ion channel 1	A, B, C	protein	531	Homo sapiens	P78348 (AlphaFold model)
Kunitz-type neurotoxin MitTx-alpha	D, F, H	protein	60	Micrurus tener tener	G9I929 (AlphaFold model)
Basic phospholipase A2 homolog MitTx-beta	E, G, I	protein	119	Micrurus tener tener	G9I930 (AlphaFold model)

Sequence of entity 1 (A, B, C), FASTA

>9E4I_1 Acid-sensing ion channel 1 (chains A, B, C)
GGRMELKAEEEEVGGVQPVSIQAFASSSTLHGLAHIFSYERLSLKRALWALCFLGSLAVL
LCVCTERVQYYFHYHHVTKLDEVAASQLTFPAVTLCNLNEFRFSQVSKNDLYHAGELLAL
LNNRYEIPDTQMADEKQLEILQDKANFRSFKPKPFNMREFYDRAGHDIRDMLLSCHFRGE
VCSAEDFKVVFTRYGKCYTFNSGRDGRPRLKTMKGGTGNGLEIMLDIQQDEYLPVWGETD
ETSFEAGIKVQIHSQDEPPFIDQLGFGVAPGFQTFVACQEQRLIYLPPPWGTCKAVTMDS
DLDFFDSYSITACRIDCETRYLVENCNCRMVHMPGDAPYCTPEQYKECADPALDFLVEKD
QEYCVCEMPCNLTRYGKELSMVKIPSKASAKYLAKKFNKSEQYIGENILVLDIFFEVLNY
ETIEQKKAYEIAGLLGDIGGQMGLFIGASILTVLELFDYAYEVIKHKLCRRGKCQKEAKR
SSADKGVALSLDDVKRHNPCESLRGHPAGMTYAANILPHHPARGTFEDFTC

Sequence of entity 2 (D, F, H), FASTA

>9E4I_2 Kunitz-type neurotoxin MitTx-alpha (chains D, F, H)
QIRPAFCYEDPPFFQKCGAFVDSYYFNRSRITCVHFFYGQCDVNQNHFTTMSECNRVCHG

Sequence of entity 3 (E, G, I), FASTA

>9E4I_3 Basic phospholipase A2 homolog MitTx-beta (chains E, G, I)
NLNQFRLMIKCTNDRVWADFVDYGCYCVARDSNTPVDDLDRCCQAQKQCYDEAVKVHGCK
PLVMFYSFECRYLASDLDCSGNNTKCRNFVCNCDRTATLCILTATYNRNNHKIDPSRCQ

Primary citation

Conformational plasticity of human acid-sensing ion channel 1a. Cahill, J., Hartfield, K.A., Heusser, S.A. et al. Nat Struct Mol Biol (2026) 33:1171-1182. DOI 10.1038/s41594-026-01845-0 · PubMed

Other PDB entries of the same protein (UniProt P78348 (AlphaFold model), which also has an AlphaFold model), best resolution first:

9E4H 2.61 Å, Human ASIC1a at pH 5.7 with rotated, domain-swapped transmembrane domain
9E4F 2.69 Å, Human ASIC1a at pH 5.7 with domain-swapped transmembrane domain
9E4A 2.74 Å, Human ASIC1a at pH 8.5 with domain-swapped transmembrane domain
9E4K 2.77 Å, Human ASIC1a at pH 8.5, T26V mutation
9E4G 2.8 Å, Human ASIC1a at pH 5.7 with linear transmembrane domain
6L6N 2.86 Å, hASIC1a co-crystallized with Nafamostat
7RNN 2.86 Å, Human ASIC1a-Nb.C1 complex
9E4J 2.87 Å, Human ASIC1a at pH 6.5 in complex with MitTx
9E4B 3.09 Å, Human ASIC1a at pH 7.5 with domain-swapped transmembrane domain
9E4E 3.16 Å, Human ASIC1a at pH 6.5 with linear transmembrane domain
9E4D 3.19 Å, Human ASIC1a at pH 7.5 with linear transmembrane domain
6L6I 3.24 Å, hASIC1a co-crystallized with Mamb-1

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