9UO4: Chimeric human IgM-Fc hexamer

Cryo-EM structure of the chimeric human IgM-Fc hexamer. Determined by electron microscopy at 3.29 Å resolution. Released 17 Dec 2025.

Method: Electron microscopy
Resolution: 3.29 Å
Organism: Homo sapiens
Chains: 12
Atoms: 19,980
Mol. weight: 493.24 kDa
Released: 17 Dec 2025

Explore 9UO4 in 3D Show helices and sheets RCSB PDB PDBe

Secondary structure: helices and β-sheets

9UO4 contains 83 α-helices and 234 β-strands across 12 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: 6 helices, 20 β-strands

Element	Residues	Length	Sheet
β-strand	347	1	1
β-strand	350	1	2
α-helix	354-357	4
β-strand	363	1	3
β-strand	366	1	2
β-strand	369	1	1
β-strand	399	1	4
β-strand	405	1	4
α-helix	406-407	2
β-strand	413	1	3
α-helix	415-419	5
β-strand	455-457	3	5
α-helix	461-466	6
β-strand	470-471	2	6
β-strand	473-475	3	5
β-strand	476-479	4	7
β-strand	485-490	6	8
β-strand	500-502	3	9
α-helix	503-504	2
β-strand	506-507	2	7
β-strand	515-517	3	7
β-strand	519-521	3	9
β-strand	522-523	2	6
α-helix	525-529	5
β-strand	534-539	6	8
β-strand	547-552	6	8

Chain B: 8 helices, 25 β-strands

Element	Residues	Length	Sheet
β-strand	347-348	2	10
α-helix	354-357	4
β-strand	363-365	3	11
β-strand	368-369	2	10
β-strand	380	1	12
β-strand	393	1	11
β-strand	399	1	13
β-strand	405	1	13
β-strand	411-413	3	11
α-helix	415-418	4
β-strand	428	1	12
β-strand	429	1	14
β-strand	434	1	14
β-strand	453-457	5	15
α-helix	458-460	3
α-helix	461-466	6
β-strand	470-471	2	16
β-strand	473-477	5	15
β-strand	485-490	6	17
β-strand	493-494	2	17
α-helix	495-496	2
β-strand	501-503	3	18
α-helix	506	1
β-strand	507	1	19
α-helix	508	1
β-strand	515	1	19
β-strand	516-517	2	15
β-strand	518-520	3	18
β-strand	522-523	2	16
α-helix	525-529	5
β-strand	534-539	6	17
β-strand	547-548	2	17
β-strand	551	1	17

Chain C: 6 helices, 18 β-strands

Element	Residues	Length	Sheet
β-strand	350	1	20
α-helix	354-359	6
β-strand	363	1	21
β-strand	366	1	20
β-strand	393	1	22
β-strand	411	1	22
β-strand	413	1	21
α-helix	415-419	5
β-strand	453-457	5	23
α-helix	461-464	4
β-strand	470-471	2	24
β-strand	473-479	7	23
β-strand	485-490	6	25
β-strand	493-495	3	25
β-strand	502-503	2	26
α-helix	506	1
β-strand	507	1	23
α-helix	508	1
β-strand	515-516	2	23
β-strand	518-519	2	26
β-strand	522-523	2	24
α-helix	525-528	4
β-strand	534-539	6	25
β-strand	547-552	6	25

Chain D: 9 helices, 24 β-strands

Element	Residues	Length	Sheet
β-strand	347	1	27
α-helix	354-359	6
β-strand	363	1	28
β-strand	369	1	27
β-strand	380-381	2	29
β-strand	394	1	30
β-strand	399	1	31
β-strand	405	1	31
β-strand	410	1	30
β-strand	413	1	28
α-helix	415-419	5
β-strand	424-425	2	32
β-strand	427-428	2	29
α-helix	436-437	2
β-strand	440-441	2	32
β-strand	453-457	5	33
α-helix	458-460	3
α-helix	461-465	5
β-strand	469-477	9	33
β-strand	479	1	34
β-strand	485-489	5	35
β-strand	494	1	35
α-helix	495-496	2
β-strand	500-502	3	33
α-helix	503-504	2
β-strand	506-507	2	34
α-helix	508	1
β-strand	515-516	2	34
β-strand	518-524	7	33
α-helix	525-529	5
β-strand	534-539	6	35
β-strand	547-548	2	35
β-strand	551-552	2	35

Chain E: 7 helices, 18 β-strands

Element	Residues	Length	Sheet
β-strand	347-350	4	36
α-helix	354-359	6
β-strand	363-364	2	37
β-strand	366-369	4	36
β-strand	380	1	38
β-strand	399	1	39
β-strand	405	1	39
β-strand	412-413	2	37
α-helix	415-419	5
β-strand	428	1	38
β-strand	453-457	5	40
α-helix	463-466	4
β-strand	470-479	10	40
β-strand	486-490	5	41
β-strand	494	1	41
α-helix	495-496	2
β-strand	500-502	3	40
α-helix	503-504	2
β-strand	506-507	2	40
α-helix	508	1
β-strand	515-517	3	40
β-strand	519-523	5	40
α-helix	525-528	4
β-strand	534-539	6	41
β-strand	547-552	6	41

Chain F: 6 helices, 17 β-strands

Element	Residues	Length	Sheet
β-strand	347	1	42
β-strand	350	1	43
α-helix	354-360	7
β-strand	363	1	44
β-strand	366	1	43
β-strand	369	1	42
β-strand	378	1	45
β-strand	413	1	44
α-helix	415-420	6
β-strand	430	1	45
β-strand	455-457	3	46
α-helix	461-466	6
β-strand	470-479	10	46
β-strand	484-490	7	47
β-strand	493-494	2	47
α-helix	495-496	2
β-strand	500-502	3	46
α-helix	503-504	2
β-strand	506-507	2	46
β-strand	515-523	9	46
α-helix	525-528	4
β-strand	534-540	7	47
β-strand	547-552	6	47

Chain G: 7 helices, 17 β-strands

Element	Residues	Length	Sheet
β-strand	348-350	3	48
α-helix	354-357	4
β-strand	363-364	2	49
β-strand	366-368	3	48
β-strand	378	1	50
β-strand	399	1	51
β-strand	405	1	51
β-strand	412-413	2	49
α-helix	415-420	6
β-strand	430	1	50
β-strand	457	1	52
α-helix	458-460	3
α-helix	461-466	6
β-strand	470-473	4	52
β-strand	476-479	4	52
β-strand	485-489	5	53
β-strand	494	1	53
α-helix	495-496	2
β-strand	501-507	7	52
α-helix	508	1
β-strand	515-523	9	52
α-helix	525-529	5
β-strand	534-539	6	53
β-strand	547-552	6	53

Chain H: 6 helices, 18 β-strands

Element	Residues	Length	Sheet
β-strand	347	1	54
β-strand	350	1	55
α-helix	354-359	6
β-strand	363-365	3	56
β-strand	366	1	55
β-strand	369	1	54
β-strand	411-413	3	56
α-helix	415-419	5
β-strand	453-457	5	57
α-helix	458-459	2
α-helix	461-464	4
β-strand	469-471	3	58
β-strand	473-477	5	57
β-strand	485-489	5	59
β-strand	494	1	59
β-strand	502	1	60
α-helix	503-504	2
β-strand	506-507	2	57
β-strand	515-517	3	57
β-strand	519	1	60
β-strand	522-524	3	58
α-helix	525-528	4
β-strand	534-539	6	59
β-strand	547-552	6	59

4 more chain groups are not listed. Open the entry in the viewer and use the sequence panel to see them.

Molecules and chains

Molecule	Chains	Type	Length	Organism	UniProt
Immunoglobulin heavy constant mu	A, B, C, D, E, F, G, H, I, J, K, L	protein	376	Homo sapiens	P01871 (AlphaFold model)

Sequence of entity 1 (A, B, C, D, E, F, G, H, I, J, K, L), FASTA

>9UO4_1 Immunoglobulin heavy constant mu (chains A, B, C, D, E, F, G, H, I, J, K, L)
ASAWSHPQFEKGGGSGGGSGGSAWSHPQFEKIDTTIAELPPKVSVFVPPRDGFFGNPRKS
KLICQATGFSPRQIQVSWLREGKQVGSGVTTDQVQAEAKESGPTTYKVTSTLTIKESDWL
GQSMFTCRVDHRGLTFQQNASSMCVPDQDTAIRVFAIPPSFASIFLTKSTKLTCLVTDLT
TYDSVTISWTRQNGEAVKTHTNISESHPNATFSAVGEASICEDDWNSGERFTCTVTHTDL
PSPLKQTISRPKGVALHRPDVYLLPPAREQLNLRESATITCLVTGFSPADVFVQWMQRGQ
PLSPEKYVTSAPMPEPQAPGRYFAHSILTVSEEEWNTGETYTCVVAHEALPNRVTERTVD
KSTGKSSLVNVNLVMS

Primary citation

Xenopus IgX informs engineering strategies of IgM and IgG hexamers. Zhang, R., Ji, C., Li, S. et al. Sci Adv (2025) 11:eaea3737-eaea3737. DOI 10.1126/sciadv.aea3737 · PubMed

Other PDB entries of the same protein (UniProt P01871 (AlphaFold model), which also has an AlphaFold model), best resolution first:

1DN0 2.28 Å, Structure of the FAB fragment from a human IgM cold agglutinin
2AGJ 2.6 Å, Crystal Structure of a glycosylated Fab from an IgM cryoglobulin with properties of a…
1HEZ 2.7 Å, Structure of P. magnus protein L bound to a human IgM Fab.
1QLR 2.83 Å, Crystal structure of the FAB fragment of a human monoclonal IgM cold agglutinin
8BPG 3.1 Å, FcMR binding at subunit Fcu3 of IgM pentamer
9UO3 3.17 Å, Cryo-EM structure of the human IgM-Fc hexamer
7YSG 3.18 Å, Cryo-EM structure of human FcmR bound to sIgM
7K0C 3.3 Å, Structure of Secretory IgM Core
7XQ8 3.3 Å, Structure of human B-cell antigen receptor of the IgM isotype
7YG2 3.32 Å, Cryo-EM structure of human IgM-Fc in complex with the J chain and the DBL domain of…
7YTC 3.39 Å, Cryo-EM structure of human FcmR bound to IgM-Fc/J
8WYR 3.39 Å, Cryo-EM structure of human CD5L bound to IgM-Fc/J

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