9UO3: Human IgM-Fc hexamer

Cryo-EM structure of the human IgM-Fc hexamer. Determined by electron microscopy at 3.17 Å resolution. Released 17 Dec 2025.

Method: Electron microscopy
Resolution: 3.17 Å
Organism: Homo sapiens
Chains: 12
Atoms: 19,980
Mol. weight: 493.97 kDa
Released: 17 Dec 2025

Explore 9UO3 in 3D Show helices and sheets RCSB PDB PDBe

Secondary structure: helices and β-sheets

9UO3 contains 85 α-helices and 219 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, 18 β-strands

Element	Residues	Length	Sheet
β-strand	346-350	5	72
α-helix	354-360	7
β-strand	364-365	2	73
β-strand	366-370	5	72
β-strand	380-383	4	74
β-strand	399	1	75
β-strand	405	1	75
β-strand	411-412	2	73
α-helix	415-419	5
β-strand	424-428	5	74
β-strand	437-441	5	74
α-helix	450-452	3
β-strand	453-457	5	76
α-helix	458-460	3
β-strand	470-479	10	76
β-strand	484-490	7	77
β-strand	493-494	2	77
α-helix	495-496	2
β-strand	500-502	3	76
β-strand	506-507	2	76
β-strand	515-523	9	76
α-helix	525-529	5
β-strand	535-540	6	77
β-strand	547-550	4	77

Chain B: 9 helices, 19 β-strands

Element	Residues	Length	Sheet
β-strand	346-350	5	65
α-helix	351-353	3
α-helix	354-360	7
β-strand	364-365	2	66
β-strand	366-370	5	65
β-strand	381-383	3	67
β-strand	399-400	2	68
β-strand	404-405	2	68
β-strand	411-412	2	66
α-helix	415-419	5
β-strand	424-428	5	67
β-strand	437-441	5	67
α-helix	451-452	2
β-strand	453-457	5	69
α-helix	458-460	3
β-strand	470-479	10	69
β-strand	484-488	5	70
β-strand	489-490	2	71
β-strand	493-494	2	71
α-helix	495-496	2
α-helix	497-499	3
β-strand	500-502	3	69
α-helix	503-505	3
β-strand	506-507	2	69
β-strand	515-523	9	69
α-helix	526-529	4
β-strand	536-540	5	70
β-strand	548-550	3	70

Chain C: 7 helices, 18 β-strands

Element	Residues	Length	Sheet
β-strand	346-350	5	1
α-helix	351-353	3
α-helix	354-360	7
β-strand	364-365	2	2
β-strand	366-370	5	1
β-strand	372	1	3
β-strand	381-383	3	4
α-helix	396-400	5
β-strand	405	1	3
β-strand	411-412	2	2
α-helix	415-419	5
β-strand	424-428	5	4
β-strand	437-441	5	4
β-strand	453-457	5	5
α-helix	458-460	3
α-helix	463-465	3
β-strand	470-479	10	5
β-strand	484-488	5	6
β-strand	489-490	2	7
β-strand	493-494	2	7
β-strand	500-507	8	5
β-strand	515-523	9	5
α-helix	525-529	5
β-strand	536-540	5	6
β-strand	547-550	4	6

Chain D: 6 helices, 18 β-strands

Element	Residues	Length	Sheet
β-strand	346-350	5	8
α-helix	351-353	3
α-helix	354-360	7
β-strand	364-365	2	9
β-strand	366-370	5	8
β-strand	379-383	5	10
β-strand	399	1	11
β-strand	405	1	11
β-strand	411-412	2	9
α-helix	415-419	5
β-strand	424-429	6	10
β-strand	437-441	5	10
β-strand	453-457	5	12
α-helix	458-460	3
β-strand	470-479	10	12
β-strand	485-490	6	13
β-strand	493-494	2	13
α-helix	495-496	2
β-strand	500-502	3	12
β-strand	515-516	2	12
β-strand	519-523	5	12
α-helix	525-529	5
β-strand	535-539	5	13
β-strand	547-550	4	13

Chain E: 7 helices, 19 β-strands

Element	Residues	Length	Sheet
β-strand	346-350	5	52
α-helix	354-360	7
β-strand	364	1	53
β-strand	366-370	5	52
β-strand	381-383	3	54
β-strand	412	1	53
α-helix	415-419	5
β-strand	424-428	5	54
β-strand	437-441	5	54
β-strand	453-457	5	55
α-helix	458-459	2
α-helix	463-465	3
β-strand	470-477	8	55
β-strand	479	1	56
β-strand	484-488	5	57
β-strand	489-490	2	58
β-strand	493-494	2	58
α-helix	495-496	2
β-strand	501-502	2	55
α-helix	503-505	3
β-strand	506-507	2	56
β-strand	515-516	2	56
β-strand	519-523	5	55
α-helix	525-529	5
β-strand	536-540	5	57
β-strand	547-550	4	57

Chain F: 6 helices, 18 β-strands

Element	Residues	Length	Sheet
β-strand	346-348	3	59
α-helix	350-353	4
α-helix	354-360	7
β-strand	364-365	2	60
β-strand	368-370	3	59
β-strand	381-383	3	61
β-strand	399	1	62
β-strand	405	1	62
β-strand	411-412	2	60
α-helix	415-419	5
β-strand	424-428	5	61
β-strand	437-441	5	61
β-strand	453-457	5	63
α-helix	458-460	3
β-strand	470-479	10	63
β-strand	484-490	7	64
β-strand	493-494	2	64
α-helix	495-496	2
β-strand	500-502	3	63
β-strand	506-507	2	63
β-strand	515-523	9	63
α-helix	525-529	5
β-strand	535-540	6	64
β-strand	547-550	4	64

Chain G: 7 helices, 18 β-strands

Element	Residues	Length	Sheet
β-strand	346-348	3	46
α-helix	351-353	3
α-helix	354-360	7
β-strand	364-365	2	47
β-strand	368-370	3	46
β-strand	379-383	5	48
β-strand	399	1	49
β-strand	405	1	49
β-strand	411-412	2	47
α-helix	415-419	5
β-strand	424-429	6	48
β-strand	437-441	5	48
α-helix	450-452	3
β-strand	453-457	5	50
α-helix	458-460	3
β-strand	470-479	10	50
β-strand	485-490	6	51
β-strand	493-494	2	51
α-helix	495-496	2
β-strand	500-502	3	50
β-strand	506-507	2	50
β-strand	515-523	9	50
α-helix	525-529	5
β-strand	535-539	5	51
β-strand	547-550	4	51

Chain H: 7 helices, 19 β-strands

Element	Residues	Length	Sheet
β-strand	346-350	5	39
α-helix	351-353	3
α-helix	354-360	7
β-strand	364-365	2	40
β-strand	366-370	5	39
β-strand	379-383	5	41
β-strand	411-412	2	40
α-helix	415-418	4
β-strand	424-429	6	41
β-strand	437-441	5	41
β-strand	453-457	5	42
α-helix	463-465	3
β-strand	469-479	11	42
β-strand	484-488	5	43
β-strand	489-490	2	44
β-strand	493-494	2	44
α-helix	495-496	2
β-strand	502	1	45
β-strand	506-507	2	42
β-strand	515-517	3	42
β-strand	519	1	45
β-strand	520-524	5	42
α-helix	525-529	5
β-strand	536-540	5	43
β-strand	547-550	4	43
α-helix	554-556	3

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
Isoform 1 of 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

>9UO3_1 Isoform 1 of Immunoglobulin heavy constant mu (chains A, B, C, D, E, F, G, H, I, J, K, L)
ASAWSHPQFEKGGGSGGGSGGSAWSHPQFEKIDTTIAELPPKVSVFVPPRDGFFGNPRKS
KLICQATGFSPRQIQVSWLREGKQVGSGVTTDQVQAEAKESGPTTYKVTSTLTIKESDWL
GQSMFTCRVDHRGLTFQQNASSMCVPDQDTAIRVFAIPPSFASIFLTKSTKLTCLVTDLT
TYDSVTISWTRQNGEAVKTHTNISESHPNATFSAVGEASICEDDWNSGERFTCTVTHTDL
PSPLKQTISRPKGVALHRPDVYLLPPAREQLNLRESATITCLVTGFSPADVFVQWMQRGQ
PLSPEKYVTSAPMPEPQAPGRYFAHSILTVSEEEWNTGETYTCVVAHEALPNRVTERTVD
KSTGKPTLYNVSLVMS

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
7YSG 3.18 Å, Cryo-EM structure of human FcmR bound to sIgM
9UO4 3.29 Å, Cryo-EM structure of the chimeric human IgM-Fc hexamer
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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