9MBZ: Human FcRL4

Cryo-EM structure of human FcRL4 bound to IgA-Fc/J. Determined by electron microscopy at 3.3 Å resolution. Released 10 Jun 2026.

Method: Electron microscopy
Resolution: 3.3 Å
Organism: Homo sapiens
Chains: 6
Atoms: 9,296
Mol. weight: 193.72 kDa
Ligands: NAG
Released: 10 Jun 2026

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

Secondary structure: helices and β-sheets

9MBZ contains 49 α-helices and 109 β-strands across 6 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: 11 helices, 18 β-strands

Element	Residues	Length	Sheet
β-strand	248-249	2	12
α-helix	250-252	3
α-helix	253-257	5
β-strand	264-266	3	12
β-strand	280-281	2	13
β-strand	290-291	2	12
β-strand	306-308	3	12
α-helix	312-316	5
α-helix	319-320	2
β-strand	321-324	4	13
β-strand	335-338	4	13
β-strand	348-352	5	14
α-helix	353-355	3
α-helix	356-360	5
β-strand	364-374	11	14
β-strand	380-385	6	15
β-strand	388-389	2	15
α-helix	390-391	2
β-strand	395-397	3	14
β-strand	401-402	2	14
α-helix	403-405	3
β-strand	411-420	10	14
α-helix	421-425	5
β-strand	430-435	6	15
β-strand	443-444	2	16
β-strand	445-448	4	15
α-helix	450-453	4
α-helix	457-458	2
β-strand	460-465	6	17

Chain B: 9 helices, 14 β-strands

Element	Residues	Length	Sheet
α-helix	247-252	6
α-helix	253-257	5
β-strand	264-265	2	18
β-strand	307-308	2	18
α-helix	312-317	6
β-strand	348-352	5	19
α-helix	353-355	3
α-helix	356-361	6
β-strand	364-365	2	20
β-strand	368-374	7	19
β-strand	380-385	6	21
β-strand	388-389	2	21
α-helix	390-391	2
β-strand	396-397	2	19
α-helix	398-399	2
β-strand	401-402	2	19
β-strand	411-416	6	19
β-strand	419-420	2	20
α-helix	421-425	5
β-strand	430-435	6	21
β-strand	443-448	6	21
α-helix	454-455	2
β-strand	460-464	5	17

Chain C: 9 helices, 20 β-strands

Element	Residues	Length	Sheet
β-strand	246-249	4	22
α-helix	250-252	3
α-helix	253-257	5
β-strand	265-268	4	22
β-strand	280-281	2	23
β-strand	290	1	22
β-strand	305	1	22
β-strand	321-324	4	23
β-strand	335-338	4	23
β-strand	350-352	3	24
α-helix	353-355	3
α-helix	356-361	6
β-strand	364-374	11	24
β-strand	380-381	2	25
β-strand	384-385	2	26
β-strand	388-389	2	26
α-helix	390-391	2
α-helix	392-394	3
β-strand	395-397	3	24
β-strand	401-402	2	24
α-helix	403-405	3
β-strand	411-420	10	24
α-helix	421-425	5
β-strand	430	1	27
β-strand	434-435	2	25
β-strand	443-444	2	25
β-strand	448	1	27
α-helix	455-456	2
β-strand	457-462	6	8

Chain D: 12 helices, 17 β-strands

Element	Residues	Length	Sheet
β-strand	247-248	2	28
α-helix	249-252	4
α-helix	253-257	5
β-strand	264-267	4	28
α-helix	288-289	2
β-strand	290	1	28
α-helix	291	1
β-strand	305-308	4	28
α-helix	312-316	5
β-strand	321-325	5	29
α-helix	333	1
β-strand	334-338	5	29
β-strand	350-352	3	30
α-helix	353-355	3
α-helix	356-361	6
β-strand	364-374	11	30
β-strand	380-385	6	31
β-strand	388-389	2	31
α-helix	390-391	2
α-helix	392-394	3
β-strand	395-397	3	30
β-strand	401-402	2	30
α-helix	403	1
β-strand	411-420	10	30
α-helix	421-425	5
β-strand	430-435	6	31
β-strand	443-448	6	31
β-strand	457-464	8	8
β-strand	470-471	2	32

Chain F: 5 helices, 29 β-strands

Element	Residues	Length	Sheet
β-strand	24-26	3	1
β-strand	33-35	3	2
β-strand	40-41	2	3
β-strand	43-45	3	1
β-strand	55-58	4	4
β-strand	68-70	3	4
β-strand	76-77	2	3
β-strand	81-83	3	5
β-strand	84-87	4	4
α-helix	90-95	6
β-strand	96-98	3	5
β-strand	99-101	3	2
β-strand	106-108	3	6
β-strand	119	1	7
β-strand	122-124	3	6
β-strand	131-138	8	8
β-strand	141-146	6	8
β-strand	151	1	6
β-strand	154	1	7
β-strand	163-171	9	8
α-helix	172-174	3
β-strand	175-178	4	8
β-strand	182-184	3	8
α-helix	186-188	3
β-strand	197	1	9
β-strand	210	1	9
α-helix	218-220	3
α-helix	223-224	2
β-strand	225-229	5	10
β-strand	230	1	11
β-strand	236	1	11
β-strand	241	1	10
β-strand	261-265	5	10
β-strand	271-272	2	10

Chain J: 3 helices, 11 β-strands

Element	Residues	Length	Sheet
β-strand	4-9	6	8
β-strand	15-22	8	8
β-strand	32-41	10	8
β-strand	46	1	33
α-helix	55	1
β-strand	56	1	33
α-helix	57	1
β-strand	59-63	5	17
α-helix	64-67	4
β-strand	74-77	4	31
β-strand	82-86	5	31
β-strand	103-104	2	32
β-strand	110-116	7	16
β-strand	121-127	7	16

Molecules and chains

Molecule	Chains	Type	Length	Organism	UniProt
Interleukin-2,Fc receptor-like protein 4	F	protein	413	Homo sapiens	P60568 (AlphaFold model), Q96PJ5 (AlphaFold model)
Interleukin-2,Isoform 1 of Immunoglobulin heavy constant alpha 1	A, B, C, D	protein	291	Homo sapiens	P01876 (AlphaFold model), P60568 (AlphaFold model)
Immunoglobulin J chain	J	protein	168	Homo sapiens	P01591 (AlphaFold model)

Sequence of entity 1 (F), FASTA

>9MBZ_1 Interleukin-2,Fc receptor-like protein 4 (chains F)
MYRMQLLSCIALSLALVTNSARIHAHKPVISVHPPWTTFFKGERVTLTCNGFQFYATEKT
TWYHRHYWGEKLTLTPGNTLEVRESGLYRCQARGSPRSNPVRLLFSSDSLILQAPYSVFE
GDTLVLRCHRRRKEKLTAVKYTWNGNILSISNKSWDLLIPQASSNNNGNYRCIGYGDEND
VFRSNFKIIKIQELFPHPELKATDSQPTEGNSVNLSCETQLPPERSDTPLHFNFFRDGEV
ILSDWSTYPELQLPTVWRENSGSYWCGAETVRGNIHKHSPSLQIHVQRIPVSGVLLETQP
SGGQAVEGEMLVLVCSVAEGTGDTTFSWHREDMQESLGRKTQRSLRAELELPAIRQSHAG
GYYCTADNSYGPVQSMVLNVTVRETPGNRDGLHHHHHHHHHHSRVDYKDDDDK

Sequence of entity 2 (A, B, C, D), FASTA

>9MBZ_2 Interleukin-2,Isoform 1 of Immunoglobulin heavy constant alpha 1 (chains A, B, C, D)
MYRMQLLSCIALSLALVTNSARIHMSAWSHPQFEKGGGSGGGSGGSAWSHPQFEKIDTTC
CHPRLSLHRPALEDLLLGSEANLTCTLTGLRDASGVTFTWTPSSGKSAVQGPPERDLCGC
YSVSSVLPGCAEPWNHGKTFTCTAAYPESKTPLTATLSKSGNTFRPEVHLLPPPSEELAL
NELVTLTCLARGFSPKDVLVRWLQGSQELPREKYLTWASRQEPSQGTTTFAVTSILRVAA
EDWKKGDTFSCMVGHEALPLAFTQKTIDRLAGKPTHVNVSVVMAEVDGTCY

Sequence of entity 3 (J), FASTA

>9MBZ_3 Immunoglobulin J chain (chains J)
MKNHLLFWGVLAVFIKAVHVKAQEDERIVLVDNKCKCARITSRIIRSSEDPNEDIVERNI
RIIVPLNNRENISDPTSPLRTRFVYHLSDLCKKCDPTEVELDNQIVTATQSNICDEDSAT
ETCYTYDRNKCYTAVVPLVYGGETKMVETALTPDACYPDYPYDVPDYA

Ligands and cofactors

ID	Name	Formula	Copies
NAG	2-acetamido-2-deoxy-beta-D-glucopyranose	C8 H15 N O6	5

Primary citation

FcRL4 is an IgA receptor that primarily binds the joining chain. Wang, Y.X., Su, C., Xiao, J.Y. To be published.

Other PDB entries of the same protein (UniProt P60568 (AlphaFold model), which also has an AlphaFold model), best resolution first:

8SOZ 1.64 Å, Structure of the complex formed by human interleukin-2 and scFv 602
8SOW 1.71 Å, Structure of the complex formed by human interleukin-2 and scFv F10
7M2G 1.79 Å, INTERLEUKIN-2 (human) mutant P65K, C125S
4NEJ 1.92 Å, Small molecular fragment bound to crystal contact interface of Interleukin-2
4NEM 1.93 Å, Small molecular fragment bound to crystal contact interface of Interleukin-2
1M48 1.95 Å, Crystal Structure of Human IL-2 Complexed with (R)-N-[2-[1-(Aminoiminomethyl)-3-piperidin…
5LQB 1.95 Å, Complex structure of human IL2 mutant, Proleukin, with Fab fragment of NARA1 antibody
1M47 1.99 Å, Crystal Structure of Human Interleukin-2
1M49 2.0 Å, Crystal Structure of Human Interleukin-2 Complexed with SP-1985
1M4B 2.15 Å, Crystal Structure of Human Interleukin-2 K43C Covalently Modified at C43 with…
1M4A 2.18 Å, Crystal Structure of Human Interleukin-2 Y31C Covalently Modified at C31 with…
1NBP 2.2 Å, Crystal Structure Of Human Interleukin-2 Y31C Covalently Modified At C31 With…

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