9TI4: Human complex I in mitochondria
High resolution Cryo-EM structure of human complex I in mitochondria. Determined by electron microscopy at 2.66 Å resolution. Released 14 Jan 2026.
- Method
- Electron microscopy
- Resolution
- 2.66 Å
- Organism
- Homo sapiens
- Chains
- 45
- Atoms
- 67,696
- Mol. weight
- 969.16 kDa
- Ligands
- SF4, FMN, PEE, 8Q1
- Released
- 14 Jan 2026
Explore 9TI4 in 3D
Show helices and sheets
RCSB PDB
PDBe
Secondary structure: helices and β-sheets
9TI4 contains 464 α-helices and 193 β-strands across 45 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: 7 helices, 2 β-strands
| Element | Residues | Length | Sheet |
|---|
| β-strand | 54 | 1 | 63 |
| α-helix | 62-88 | 27 | |
| α-helix | 89-93 | 5 | |
| β-strand | 98 | 1 | 64 |
| α-helix | 100-102 | 3 | |
| α-helix | 109-112 | 4 | |
| α-helix | 116-124 | 9 | |
| α-helix | 127-128 | 2 | |
| α-helix | 129-163 | 35 | |
Chain b: 6 helices, 3 β-strands
| Element | Residues | Length | Sheet |
|---|
| α-helix | 6-23 | 18 | |
| β-strand | 27 | 1 | 63 |
| α-helix | 43-51 | 9 | |
| α-helix | 57-71 | 15 | |
| α-helix | 72-76 | 5 | |
| α-helix | 77-92 | 16 | |
| β-strand | 97-99 | 3 | 26 |
| α-helix | 100-103 | 4 | |
| β-strand | 109 | 1 | 65 |
Chain c: 8 helices, 5 β-strands
| Element | Residues | Length | Sheet |
|---|
| α-helix | 34-36 | 3 | |
| α-helix | 45-54 | 10 | |
| β-strand | 64 | 1 | 66 |
| α-helix | 65-66 | 2 | |
| β-strand | 76 | 1 | 66 |
| α-helix | 83-85 | 3 | |
| β-strand | 94 | 1 | 67 |
| β-strand | 99 | 1 | 67 |
| α-helix | 109-112 | 4 | |
| α-helix | 126-149 | 24 | |
| β-strand | 152 | 1 | 68 |
| α-helix | 158-160 | 3 | |
| α-helix | 162-166 | 5 | |
Chain C: 26 helices, 17 β-strands
| Element | Residues | Length | Sheet |
|---|
| α-helix | 37-39 | 3 | |
| α-helix | 57-59 | 3 | |
| α-helix | 65-68 | 4 | |
| α-helix | 73-83 | 11 | |
| β-strand | 86 | 1 | 1 |
| β-strand | 94 | 1 | 1 |
| α-helix | 95-101 | 7 | |
| α-helix | 104-106 | 3 | |
| β-strand | 107 | 1 | 2 |
| β-strand | 109 | 1 | 2 |
| β-strand | 112-117 | 6 | 3 |
| α-helix | 127-133 | 7 | |
| α-helix | 135-149 | 15 | |
| β-strand | 153-158 | 6 | 3 |
| α-helix | 163-179 | 17 | |
| β-strand | 183 | 1 | 4 |
| α-helix | 186-188 | 3 | |
| β-strand | 193 | 1 | 4 |
| β-strand | 195-199 | 5 | 3 |
| α-helix | 204-207 | 4 | |
| α-helix | 209-217 | 9 | |
| α-helix | 223-225 | 3 | |
| α-helix | 235-237 | 3 | |
| β-strand | 240-244 | 5 | 3 |
| α-helix | 245-255 | 11 | |
| α-helix | 260-263 | 4 | |
| β-strand | 273-280 | 8 | 5 |
| β-strand | 286-291 | 6 | 5 |
| β-strand | 295 | 1 | 6 |
| α-helix | 296-302 | 7 | |
| α-helix | 311-313 | 3 | |
| β-strand | 314-318 | 5 | 5 |
| β-strand | 327-328 | 2 | 5 |
| α-helix | 329-332 | 4 | |
| β-strand | 336 | 1 | 6 |
| α-helix | 339-344 | 6 | |
| β-strand | 353-358 | 6 | 5 |
| α-helix | 363-375 | 13 | |
| α-helix | 383 | 1 | |
| α-helix | 384-388 | 5 | |
| α-helix | 389-401 | 13 | |
| α-helix | 408-420 | 13 | |
| α-helix | 427-456 | 30 | |
Chain d: 11 helices, 3 β-strands
| Element | Residues | Length | Sheet |
|---|
| α-helix | 3-6 | 4 | |
| α-helix | 13-15 | 3 | |
| β-strand | 18 | 1 | 65 |
| α-helix | 19-21 | 3 | |
| α-helix | 22-31 | 10 | |
| α-helix | 32-36 | 5 | |
| α-helix | 37-52 | 16 | |
| β-strand | 57 | 1 | 64 |
| α-helix | 62-64 | 3 | |
| β-strand | 72 | 1 | 7 |
| α-helix | 76-111 | 36 | |
| α-helix | 112-114 | 3 | |
| α-helix | 119-137 | 19 | |
| α-helix | 146-169 | 24 | |
Chain D: 8 helices, 9 β-strands
| Element | Residues | Length | Sheet |
|---|
| β-strand | 36-38 | 3 | 8 |
| α-helix | 48-60 | 13 | |
| α-helix | 62-75 | 14 | |
| α-helix | 78-79 | 2 | |
| β-strand | 99-101 | 3 | 9 |
| β-strand | 103 | 1 | 10 |
| β-strand | 109 | 1 | 10 |
| α-helix | 116-120 | 5 | |
| β-strand | 126-132 | 7 | 11 |
| β-strand | 138-146 | 9 | 11 |
| α-helix | 155-159 | 5 | |
| β-strand | 165-167 | 3 | 9 |
| β-strand | 175 | 1 | 12 |
| α-helix | 179-181 | 3 | |
| β-strand | 182-183 | 2 | 11 |
| α-helix | 185-194 | 10 | |
| α-helix | 196-206 | 11 | |
Chain e: 9 helices, 1 β-strand
| Element | Residues | Length | Sheet |
|---|
| α-helix | 46-48 | 3 | |
| β-strand | 56 | 1 | 13 |
| α-helix | 58-61 | 4 | |
| α-helix | 66-69 | 4 | |
| α-helix | 80-89 | 10 | |
| α-helix | 90-102 | 13 | |
| α-helix | 103-107 | 5 | |
| α-helix | 116-131 | 16 | |
| α-helix | 144-146 | 3 | |
| α-helix | 148-150 | 3 | |
Chain E: 11 helices, 9 β-strands
| Element | Residues | Length | Sheet |
|---|
| α-helix | 58-76 | 19 | |
| β-strand | 81 | 1 | 12 |
| β-strand | 82 | 1 | 14 |
| β-strand | 85 | 1 | 12 |
| α-helix | 89-97 | 9 | |
| α-helix | 103-106 | 4 | |
| β-strand | 111 | 1 | 14 |
| β-strand | 119-123 | 5 | 12 |
| β-strand | 127 | 1 | 15 |
| α-helix | 131-140 | 10 | |
| α-helix | 142 | 1 | |
| β-strand | 146-150 | 5 | 12 |
| α-helix | 151-156 | 6 | |
| α-helix | 158-160 | 3 | |
| β-strand | 166 | 1 | 15 |
| α-helix | 170-172 | 3 | |
| β-strand | 178-180 | 3 | 12 |
| α-helix | 185-186 | 2 | |
| α-helix | 187-202 | 16 | |
| α-helix | 206-211 | 6 | |
37 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 |
|---|
| NADH dehydrogenase [ubiquinone] flavoprotein 1, mitochondrial | C | protein | 434 | Homo sapiens | P49821 (AlphaFold model) |
| NADH dehydrogenase [ubiquinone] iron-sulfur protein 8, mitochondrial | D | protein | 176 | Homo sapiens | O00217 (AlphaFold model) |
| NADH dehydrogenase [ubiquinone] iron-sulfur protein 7, mitochondrial | E | protein | 161 | Homo sapiens | O75251 (AlphaFold model) |
| NADH dehydrogenase [ubiquinone] 1 alpha subcomplex subunit 6 | F | protein | 118 | Homo sapiens | P56556 (AlphaFold model) |
| NADH dehydrogenase [ubiquinone] 1 alpha subcomplex subunit 2 | G | protein | 85 | Homo sapiens | O43678 |
| Acyl carrier protein, mitochondrial | H, X | protein | 86 | Homo sapiens | O14561 |
| NADH dehydrogenase [ubiquinone] 1 alpha subcomplex subunit 5 | I | protein | 112 | Homo sapiens | Q16718 |
| NADH dehydrogenase [ubiquinone] 1 alpha subcomplex subunit 9, mitochondrial | J | protein | 341 | Homo sapiens | Q16795 |
| NADH dehydrogenase [ubiquinone] flavoprotein 3, mitochondrial | K | protein | 39 | Homo sapiens | P56181 |
| NADH dehydrogenase [ubiquinone] iron-sulfur protein 4, mitochondrial | L | protein | 121 | Homo sapiens | O43181 |
| NADH-ubiquinone oxidoreductase 75 kDa subunit, mitochondrial | M | protein | 687 | Homo sapiens | P28331 |
| NADH dehydrogenase [ubiquinone] 1 alpha subcomplex subunit 12 | N | protein | 144 | Homo sapiens | Q9UI09 |
32 more molecules are not listed.
Sequence of entity 1 (C), FASTA
>9TI4_1 NADH dehydrogenase [ubiquinone] flavoprotein 1, mitochondrial (chains C)
PKKTSFGSLKDEDRIFTNLYGRHDWRLKGSLSRGDWYKTKEILLKGPDWILGEIKTSGLR
GRGGAGFPTGLKWSFMNKPSDGRPKYLVVNADEGEPGTCKDREILRHDPHKLLEGCLVGG
RAMGARAAYIYIRGEFYNEASNLQVAIREAYEAGLIGKNACGSGYDFDVFVVRGAGAYIC
GEETALIESIEGKQGKPRLKPPFPADVGVFGCPTTVANVETVAVSPTICRRGGTWFAGFG
RERNSGTKLFNISGHVNHPCTVEEEMSVPLKELIEKHAGGVTGGWDNLLAVIPGGSSTPL
IPKSVCETVLMDFDALVQAQTGLGTAAVIVMDRSTDIVKAIARLIEFYKHESCGQCTPCR
EGVDWMNKVMARFVRGDARPAEIDSLWEISKQIEGHTICALGDGAAWPVQGLIRHFRPEL
EERMQRFAQQHQAR
Sequence of entity 2 (D), FASTA
>9TI4_2 NADH dehydrogenase [ubiquinone] iron-sulfur protein 8, mitochondrial (chains D)
TYKYVNMQDPEMDMKSVTDRAARTLLWTELFRGLGMTLSYLFREPATINYPFEKGPLSPR
FRGEHALRRYPSGEERCIACKLCEAICPAQAITIEAEPRADGSRRTTRYDIDMTKCIYCG
FCQEACPVDAIVEGPNFEFSTETHEELLYNKEKLLNNGDKWEAEIAANIQADYLYR
Sequence of entity 3 (E), FASTA
>9TI4_3 NADH dehydrogenase [ubiquinone] iron-sulfur protein 7, mitochondrial (chains E)
APKPSSRGEYVVAKLDDLVNWARRSSLWPMTFGLACCAVEMMHMAAPRYDMDRFGVVFRA
SPRQSDVMIVAGTLTNKMAPALRKVYDQMPEPRYVVSMGSCANGGGYYHYSYSVVRGCDR
IVPVDIYIPGCPPTAEALLYGILQLQRKIKRERRLQIWYRR
Sequence of entity 4 (F), FASTA
>9TI4_4 NADH dehydrogenase [ubiquinone] 1 alpha subcomplex subunit 6 (chains F)
STASTFVKPIFSRDMNEAKRRVRELYRAWYREVPNTVHQFQLDITVKMGRDKVREMFMKN
AHVTDPRVVDLLVIKGKIELEETIKVWKQRTHVMRFFHETEAPRPKDFLSKFYVGHDP
Sequence of entity 5 (G), FASTA
>9TI4_5 NADH dehydrogenase [ubiquinone] 1 alpha subcomplex subunit 2 (chains G)
LGLREIRIHLCQRSPGSQGVRDFIEKRYVELKKANPDLPILIRECSDVQPKLWARYAFGQ
ETNVPLNNFSADQVTRALENVLSGK
Sequence of entity 6 (H, X), FASTA
>9TI4_6 Acyl carrier protein, mitochondrial (chains H, X)
MPPLTLEGIQDRVLYVLKLYDKIDPEKLSVNSHFMKDLGLDSLDQVEIIMAMEDEFGFEI
PDIDAEKLMCPQEIVDYIADKKDVYE
Sequence of entity 7 (I), FASTA
>9TI4_7 NADH dehydrogenase [ubiquinone] 1 alpha subcomplex subunit 5 (chains I)
LKKTTGLVGLAVCNTPHERLRILYTKILDVLEEIPKNAAYRKYTEQITNEKLAMVKAEPD
VKKLEDQLQGGQLEEVILQAEHELNLARKMREWKLWEPLVEEPPADQWKWPI
Sequence of entity 8 (J), FASTA
>9TI4_8 NADH dehydrogenase [ubiquinone] 1 alpha subcomplex subunit 9, mitochondrial (chains J)
LHHALMPHGKGGRSSVSGIVATVFGATGFLGRYVVNHLGRMGSQVIIPYRCDKYDIMHLR
PMGDLGQLLFLEWDARDKDSIRRVVQHSNVVINLIGRDWETKNFDFEDVFVKIPQAIAQL
SKEAGVEKFIHVSHLNANIKSSSRYLRNKAVGEKVVRDAFPEAIIVKPSDIFGREDRFLN
SFASMHRFGPIPLGSLGWKTVKQPVYVVDVSKGIVNAVKDPDANGKSFAFVGPSRYLLFH
LVKYIFAVAHRLFLPFPLPLFAYRWVARVFEISPFEPWITRDKVERMHITDMKLPHLPGL
EDLGIQATPLELKAIEVLRRHRTYRWLSAEIEDVKPAKTVN
Sequence of entity 9 (K), FASTA
>9TI4_9 NADH dehydrogenase [ubiquinone] flavoprotein 3, mitochondrial (chains K)
NTTYKNLQHHDYSTYTFLDLNLELSKFRMPQPSSGRESP
Sequence of entity 10 (L), FASTA
>9TI4_10 NADH dehydrogenase [ubiquinone] iron-sulfur protein 4, mitochondrial (chains L)
VDEKLDITTLTGVPEEHIKTRKVRIFVPARNNMQSGVNNTKKWKMEFDTRERWENPLMGW
ASTADPLSNMVLTFSTKEDAVSFAEKNGWSYDIEERKVPKPKSKSYGANFSWNKRTRVST
K
Sequence of entity 11 (M), FASTA
>9TI4_11 NADH-ubiquinone oxidoreductase 75 kDa subunit, mitochondrial (chains M)
NLIEVFVDGQSVMVEPGTTVLQACEKVGMQIPRFCYHERLSVAGNCRMCLVEIEKAPKVV
AACAMPVMKGWNILTNSEKSKKAREGVMEFLLANHPLDCPICDQGGECDLQDQSMMFGND
RSRFLEGKRAVEDKNIGPLVKTIMTRCIQCTRCIRFASEIAGVDDLGTTGRGNDMQVGTY
IEKMFMSELSGNIIDICPVGALTSKPYAFTARPWETRKTESIDVMDAVGSNIVVSTRTGE
VMRILPRMHEDINEEWISDKTRFAYDGLKRQRLTEPMVRNEKGLLTYTSWEDALSRVAGM
LQSFQGKDVAAIAGGLVDAEALVALKDLLNRVDSDTLCTEEVFPTAGAGTDLRSNYLLNT
TIAGVEEADVVLLVGTNPRFEAPLFNARIRKSWLHNDLKVALIGSPVDLTYTYDHLGDSP
KILQDIASGSHPFSQVLKEAKKPMVVLGSSALQRNDGAAILAAVSSIAQKIRMTSGVTGD
WKVMNILHRIASQVAALDLGYKPGVEAIRKNPPKVLFLLGADGGCITRQDLPKDCFIIYQ
GHHGDVGAPIADVILPGAAYTEKSATYVNTEGRAQQTKVAVTPPGLAREDWKIIRALSEI
AGMTLPYDTLDQVRNRLEEVSPNLVRYDDIEGANYFQQANELSKLVNQQLLADPLVPPQL
TIKDFYMTDSISRASQTMAKCVKAVTE
Sequence of entity 12 (N), FASTA
>9TI4_12 NADH dehydrogenase [ubiquinone] 1 alpha subcomplex subunit 12 (chains N)
MELVQVLKRGLQQITGHGGLRGYLRVFFRTNDAKVGTLVGEDKYGNKYYEDNKQFFGRHR
WVVYTTEMNGKNTFWDVDGSMVPPEWHRWLHSMTDDPPTTKPLTARKFIWTNHKFNVTGT
PEQYVPYSTTRKKIQEWIPPSTPY
Ligands and cofactors
| ID | Name | Formula | Copies |
|---|
| SF4 | Iron/sulfur cluster | Fe4 S4 | 6 |
| FMN | Flavin mononucleotide | C17 H21 N4 O9 P | 1 |
| PEE | 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine | C41 H78 N O8 P | 7 |
| 8Q1 | S-[2-({N-[(2R)-2-hydroxy-3,3-dimethyl-4-(phosphonooxy)butanoyl]-beta-alanyl}ami… | C23 H45 N2 O8 P S | 2 |
| NDP | NADPH dihydro-nicotinamide-adenine-dinucleotide phosphate | C21 H30 N7 O17 P3 | 1 |
| FES | FE2/S2 (inorganic) cluster | Fe2 S2 | 2 |
| ZN | Zinc ion | Zn | 1 |
| CDL | Cardiolipin | C81 H156 O17 P2 | 6 |
| DGT | 2'-deoxyguanosine-5'-triphosphate | C10 H16 N5 O13 P3 | 1 |
| MG | Magnesium ion | Mg | 1 |
| PLX | (9R,11S)-9-({[(1S)-1-hydroxyhexadecyl]oxy}methyl)-2,2-dimethyl-5,7,10-trioxa-2L… | C42 H89 N O8 P | 7 |
Primary citation
Structural basis for late maturation steps of mitochondrial respiratory chain complex IV within the human respirasome. Nguyen, M.D., Sierra-Magro, A., Singh, V. et al. Nat Commun (2026) 17:1550-1550. DOI 10.1038/s41467-025-68274-3 · PubMed
Other PDB entries of the same protein (UniProt P49821 (AlphaFold model), which also has an AlphaFold model), best resolution first:
- 9I4I 2.63 Å, High resolution Cryo-EM structure of human complex I in mitochondria
- 5XTB 3.4 Å, Cryo-EM structure of human respiratory complex I matrix arm
- 9CWT 3.44 Å, Human kidney respiratory complex I
- 5XTD 3.7 Å, Cryo-EM structure of human respiratory complex I
- 5XTH 3.9 Å, Cryo-EM structure of human respiratory supercomplex I1III2IV1
- 5XTI 17.4 Å, Cryo-EM architecture of human respiratory chain megacomplex-I2III2IV2
Browse structure collections
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