9K3F: PDB entry 9K3F

Cryo-EM structure of the unliganded human melanocortin receptor 3 (MC3R)-Gs complex. Determined by electron microscopy at 2.75 Å resolution. Released 6 Aug 2025.

Method: Electron microscopy
Resolution: 2.75 Å
Organisms: Homo sapiens, synthetic construct, Bos taurus
Chains: 5
Atoms: 8,743
Mol. weight: 175 kDa
Released: 6 Aug 2025

Explore 9K3F in 3D Show helices and sheets RCSB PDB PDBe

Secondary structure: helices and β-sheets

9K3F contains 34 α-helices and 62 β-strands across 5 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, 11 β-strands

Element	Residues	Length	Sheet
α-helix	14-37	24
β-strand	41-42	2	1
β-strand	45-47	3	2
α-helix	53-61	9
β-strand	207	1	3
β-strand	210-213	4	1
β-strand	218-221	4	1
β-strand	223	1	2
β-strand	224	1	3
α-helix	234-236	3
β-strand	243-249	7	2
α-helix	253-265	3
α-helix	266-277	12
β-strand	286-292	7	2
α-helix	294-302	9
α-helix	308-311	4
α-helix	314-317	4
α-helix	326-327	2
α-helix	332-350	19
β-strand	359-360	2	2
β-strand	363-364	2	2
α-helix	372-390	19

Chain B: 4 helices, 29 β-strands

Element	Residues	Length	Sheet
α-helix	4-24	21
α-helix	30-34	5
α-helix	38-40	3
β-strand	46-51	6	4
β-strand	58-63	6	5
β-strand	69-74	6	5
β-strand	78-83	6	5
β-strand	88-94	7	5
α-helix	95	1
β-strand	100-105	6	6
β-strand	111-116	6	6
β-strand	121-125	5	6
β-strand	134-139	6	6
β-strand	146-151	6	7
β-strand	156-161	6	7
β-strand	165-170	6	7
β-strand	178-180	3	7
β-strand	189-192	4	8
β-strand	196	1	8
β-strand	198-202	5	8
β-strand	208-212	5	8
β-strand	218-222	5	8
β-strand	229-234	6	9
β-strand	240-245	6	9
β-strand	250-254	5	9
β-strand	259-264	6	9
β-strand	273-278	6	10
β-strand	284-289	6	10
β-strand	294-298	5	10
β-strand	306-308	3	10
β-strand	315-320	6	4
β-strand	327-331	5	4
β-strand	336-340	5	4

Chain G: 3 helices, 0 β-strands

Element	Residues	Length
α-helix	10-23	14
α-helix	30-43	14
α-helix	53-55	3

Chain R: 11 helices, 0 β-strands

Element	Residues	Length
α-helix	43-64	22
α-helix	72-102	31
α-helix	113-147	35
α-helix	149-151	3
α-helix	158-181	24
α-helix	188-196	9
α-helix	201-222	22
α-helix	238-265	28
α-helix	272-278	7
α-helix	281-298	18
α-helix	304-309	6

Chain S: 5 helices, 22 β-strands

Element	Residues	Length	Sheet
β-strand	4-7	4	11
β-strand	11-12	2	12
β-strand	17-24	8	11
α-helix	29-31	3
β-strand	33-39	7	13
β-strand	45-51	7	13
α-helix	53-55	3
β-strand	58-60	3	13
β-strand	68-73	6	11
β-strand	78-84	7	11
α-helix	88-90	3
β-strand	92-99	8	13
β-strand	110-111	2	13
β-strand	115-117	3	13
β-strand	118-119	2	12
β-strand	140-141	2	14
β-strand	146-148	3	15
α-helix	153-154	2
β-strand	155-161	7	14
β-strand	174-179	6	15
β-strand	187-189	3	15
β-strand	204-207	4	14
β-strand	211-216	6	14
β-strand	225-231	7	15
α-helix	237	1
β-strand	239	1	15
β-strand	244-246	3	15

Molecules and chains

Molecule	Chains	Type	Length	Organism	UniProt
Melanocortin receptor 3,Melanocortin receptor 3,Melanocortin receptor 3,LgBiT subunit	R	protein	496	Homo sapiens, synthetic construct	P41968 (AlphaFold model)
Guanine nucleotide-binding protein G(i) subunit alpha-1,Guanine nucleotide-binding protein G(s)…	A	protein	361	Homo sapiens	P63092 (AlphaFold model), P63096 (AlphaFold model)
Guanine nucleotide-binding protein G(I)/G(S)/G(T) subunit beta-1,Guanine nucleotide-binding…	B	protein	371	Homo sapiens, synthetic construct	P62873 (AlphaFold model)
Guanine nucleotide-binding protein G(I)/G(S)/G(O) subunit gamma-2	G	protein	71	Bos taurus	P63212
scFv16	S	protein	285	synthetic construct

Sequence of entity 1 (R), FASTA

>9K3F_1 Melanocortin receptor 3,Melanocortin receptor 3,Melanocortin receptor 3,LgBiT subunit (chains R)
MNASCCLPSVQPTLPNGSEHLQAPFFSNQSSSAFCEQVFIKPEVFLSLGIVSLLENILVI
LAVVRNGNLHSPMYFFLCSLAVADMLVSVSNALETIMIAIVHSDYLTFEDQFIQHMDNIF
DSMICISLVASICNLLAIAVDRYVTIFYALRYHSIMTVRKALTLIVAIWVCCGVCGVVFI
VYSESKMVIVCLITMFFAMMLLMGTLYVHMFLFARLHVKRIAALPPADGVAPQQHSCMKG
AVTITILLGVFIFCWAPFFLHLVLIITCPTNPYCICYTAHFNTYLVLIMCNSVIDPLIYA
FRSLELRNTFREILCGCNGMNLGGSSGGGGSGGGGSSGVFTLEDFVGDWEQTAAYNLDQV
LEQGGVSSLLQNLAVSVTPIQRIVRSGENALKIDIHVIIPYEGLSADQMAQIEEVFKVVY
PVDDHHFKVILPYGTLVIDGVTPNMLNYFGRPYEGIAVFDGKKITVTGTLWNGNKIIDER
LITPDGSMLFRVTINS

Sequence of entity 2 (A), FASTA

>9K3F_2 Guanine nucleotide-binding protein G(i) subunit alpha-1,Guanine nucleotide-binding protein G(s) subunit alpha isoforms short (chains A)
MGCTLSAEDKAAVERSKMIEKQLQKDKQVYRATHRLLLLGADNSGKSTIVKQMRIYHVNG
YSEEECKQYKAVVYSNTIQSIIAIIRAMGRLKIDFGDSARADDARQLFVLAGAAEEGFMT
AELAGVIKRLWKDSGVQACFNRSREYQLNDSAAYYLNDLDRIAQPNYIPTQQDVLRTRVK
TSGIFETKFQVDKVNFHMFDVGAQRDERRKWIQCFNDVTAIIFVVDSSDYNRLQEALNDF
KSIWNNRWLRTISVILFLNKQDLLAEKVLAGKSKIEDYFPEFARYTTPEDATPEPGEDPR
VTRAKYFIRDEFLRISTASGDGRHYCYPHFTCSVDTENARRIFNDCRDIIQRMHLRQYEL
L

Sequence of entity 3 (B), FASTA

>9K3F_3 Guanine nucleotide-binding protein G(I)/G(S)/G(T) subunit beta-1,Guanine nucleotide-binding protein G(I)/G(S)/G(T) subunit beta-1,Guanine nucleotide-binding protein G(I)/G(S)/G(T) subunit beta-1,HiBiT (chains B)
MGSLLQSELDQLRQEAEQLKNQIRDARKACADATLSQITNNIDPVGRIQMRTRRTLRGHL
AKIYAMHWGTDSRLLVSASQDGKLIIWDSYTTNKVHAIPLRSSWVMTCAYAPSGNYVACG
GLDNICSIYNLKTREGNVRVSRELAGHTGYLSCCRFLDDNQIVTSSGDTTCALWDIETGQ
QTTTFTGHTGDVMSLSLAPDTRLFVSGACDASAKLWDVREGMCRQTFTGHESDINAICFF
PNGNAFATGSDDATCRLFDLRADQELMTYSHDNIICGITSVSFSKSGRLLLAGYDDFNCN
VWDALKADRAGVLAGHDNRVSCLGVTDDGMAVATGSWDSFLKIWNGSSGGGGSGGGGSSG
VSGWRLFKKIS

Sequence of entity 4 (G), FASTA

>9K3F_4 Guanine nucleotide-binding protein G(I)/G(S)/G(O) subunit gamma-2 (chains G)
MASNNTASIAQARKLVEQLKMEANIDRIKVSKAAADLMAYCEAHAKEDPLLTPVPASENP
FREKKFFCAIL

Sequence of entity 5 (S), FASTA

>9K3F_5 scFv16 (chains S)
MLLVNQSHQGFNKEHTSKMVSAIVLYVLLAAAAHSAFAVQLVESGGGLVQPGGSRKLSCS
ASGFAFSSFGMHWVRQAPEKGLEWVAYISSGSGTIYYADTVKGRFTISRDDPKNTLFLQM
TSLRSEDTAMYYCVRSIYYYGSSPFDFWGQGTTLTVSAGGGGSGGGGSGGGGSADIVMTQ
ATSSVPVTPGESVSISCRSSKSLLHSNGNTYLYWFLQRPGQSPQLLIYRMSNLASGVPDR
FSGSGSGTAFTLTISRLEAEDVGVYYCMQHLEYPLTFGAGTKLEL

Primary citation

Structural basis for the constitutive activity of the melanocortin receptor family. Feng, W., Zhou, Q., Zheng, C. et al. Structure (2025) 33:1074-1087.e5. DOI 10.1016/j.str.2025.03.004 · PubMed

Other PDB entries of the same protein (UniProt P41968 (AlphaFold model), which also has an AlphaFold model), best resolution first:

8IOC 2.86 Å, Cryo-EM structure of the gamma-MSH-bound human melanocortin receptor 3 (MC3R)-Gs complex
8W8W 2.9 Å, Cryo-EM structure of alpha-MSH-MC3R-Gs_Nb35 complex
8W8X 2.9 Å, Cryo-EM structure of beta-MSH-MC3R-Gs_Nb35 complex
8W8Y 2.9 Å, Cryo-EM structure of gamma-MSH-MC3R-Gs_Nb35 complex
8KIG 3.1 Å, Cryo-EM structure of MC3R in complex with SHU9119

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