UniProtKB - O35625 (AXIN1_MOUSE)
Axin-1
Axin1
Functioni
GO - Molecular functioni
- armadillo repeat domain binding Source: MGI
- beta-catenin binding Source: MGI
- enzyme binding Source: MGI
- identical protein binding Source: MGI
- I-SMAD binding Source: BHF-UCL
- molecular adaptor activity Source: BHF-UCL
- p53 binding Source: MGI
- protein C-terminus binding Source: MGI
- protein domain specific binding Source: MGI
- protein homodimerization activity Source: UniProtKB
- protein kinase binding Source: ParkinsonsUK-UCL
- protein self-association Source: MGI
- R-SMAD binding Source: MGI
- signaling receptor binding Source: MGI
- signaling receptor complex adaptor activity Source: MGI
- SMAD binding Source: MGI
- ubiquitin protein ligase binding Source: BHF-UCL
GO - Biological processi
- activation of protein kinase activity Source: MGI
- apoptotic process Source: UniProtKB-KW
- axial mesoderm development Source: MGI
- axial mesoderm formation Source: MGI
- canonical Wnt signaling pathway Source: MGI
- cellular protein-containing complex assembly Source: MGI
- cytoplasmic microtubule organization Source: MGI
- dorsal/ventral axis specification Source: MGI
- dorsal/ventral pattern formation Source: MGI
- genetic imprinting Source: MGI
- head development Source: MGI
- in utero embryonic development Source: MGI
- negative regulation of canonical Wnt signaling pathway Source: MGI
- negative regulation of fat cell differentiation Source: MGI
- negative regulation of gene expression Source: MGI
- negative regulation of protein metabolic process Source: MGI
- negative regulation of transcription elongation from RNA polymerase II promoter Source: MGI
- negative regulation of Wnt signaling pathway Source: MGI
- nucleocytoplasmic transport Source: MGI
- positive regulation of JNK cascade Source: UniProtKB
- positive regulation of JUN kinase activity Source: MGI
- positive regulation of peptidyl-serine phosphorylation Source: ParkinsonsUK-UCL
- positive regulation of peptidyl-threonine phosphorylation Source: ParkinsonsUK-UCL
- positive regulation of proteasomal ubiquitin-dependent protein catabolic process Source: MGI
- positive regulation of protein catabolic process Source: MGI
- positive regulation of protein kinase activity Source: CACAO
- positive regulation of protein phosphorylation Source: MGI
- positive regulation of protein ubiquitination Source: MGI
- positive regulation of transcription, DNA-templated Source: BHF-UCL
- positive regulation of transforming growth factor beta receptor signaling pathway Source: MGI
- positive regulation of ubiquitin-dependent protein catabolic process Source: MGI
- positive regulation of ubiquitin-protein transferase activity Source: BHF-UCL
- post-anal tail morphogenesis Source: MGI
- protein catabolic process Source: MGI
- protein polyubiquitination Source: MGI
- regulation of canonical Wnt signaling pathway Source: MGI
- regulation of protein phosphorylation Source: MGI
- sensory perception of sound Source: MGI
- Wnt signaling pathway Source: MGI
Keywordsi
Molecular function | Developmental protein |
Biological process | Apoptosis, Wnt signaling pathway |
Enzyme and pathway databases
Reactomei | R-MMU-195253, Degradation of beta-catenin by the destruction complex R-MMU-196299, Beta-catenin phosphorylation cascade R-MMU-201681, TCF dependent signaling in response to WNT R-MMU-4641257, Degradation of AXIN R-MMU-4641262, Disassembly of the destruction complex and recruitment of AXIN to the membrane R-MMU-5689880, Ub-specific processing proteases |
Names & Taxonomyi
Protein namesi | Recommended name: Axin-1Alternative name(s): Axis inhibition protein 1 Protein Fused |
Gene namesi | Name:Axin1 Synonyms:Axin, Fu |
Organismi | Mus musculus (Mouse) |
Taxonomic identifieri | 10090 [NCBI] |
Taxonomic lineagei | Eukaryota › Metazoa › Chordata › Craniata › Vertebrata › Euteleostomi › Mammalia › Eutheria › Euarchontoglires › Glires › Rodentia › Myomorpha › Muroidea › Muridae › Murinae › Mus › Mus |
Proteomesi |
|
Organism-specific databases
MGIi | MGI:1096327, Axin1 |
Subcellular locationi
Nucleus
- Nucleus By similarity
Cytoplasm and Cytosol
- Cytoplasm 2 Publications
Plasma membrane
- Cell membrane 1 Publication
Other locations
- Membrane 1 Publication
Note: On UV irradiation, translocates to the nucleus and colocalizes with DAAX (By similarity). MACF1 is required for its translocation to cell membrane (PubMed:16815997).By similarity1 Publication
Cytoskeleton
- microtubule cytoskeleton Source: MGI
Cytosol
- cytosol Source: Reactome
Nucleus
- nucleus Source: MGI
Plasma Membrane
- lateral plasma membrane Source: MGI
- plasma membrane Source: UniProtKB
Other locations
- beta-catenin destruction complex Source: MGI
- cell cortex Source: MGI
- cell periphery Source: MGI
- cytoplasm Source: BHF-UCL
- cytoplasmic vesicle Source: MGI
- perinuclear region of cytoplasm Source: MGI
- postsynaptic density Source: MGI
- protein-containing complex Source: MGI
- Wnt signalosome Source: ParkinsonsUK-UCL
Keywords - Cellular componenti
Cell membrane, Cytoplasm, Membrane, NucleusPathology & Biotechi
Mutagenesis
Feature key | Position(s) | DescriptionActions | Graphical view | Length |
---|---|---|---|---|
Mutagenesisi | 480 | T → A: Greatly reduced GSK3B-mediated phosphorylation; when associated with A-485 and A-492. 1 Publication | 1 | |
Mutagenesisi | 485 | S → A: Greatly reduced GSK3B-mediated phosphorylation and large effect on the inhibitory activity in Wnt-signaling; when associated with A-480 and A-492. 1 Publication | 1 | |
Mutagenesisi | 492 | S → A: Greatly reduced GSK3B-mediated phosphorylation; when associated with A-480 and A-485. 1 Publication | 1 | |
Mutagenesisi | 492 | S → I: Little effect on inhibitory activity on Wnt-signaling. 1 Publication | 1 | |
Mutagenesisi | 495 | S → A: No effect on phosphorylation. Little effect on inhibitory activity on Wnt-signaling. 1 Publication | 1 | |
Mutagenesisi | 858 – 863 | Missing : Abolishes binding of PIAS1 and PIAS2. Dramatically reduces sumoylation and abolishes AXIN1-mediated JNK activation. No effect on homodimerization nor on Wnt-signaling. 1 Publication | 6 | |
Mutagenesisi | 858 | K → A: Decreased sumoylation followed by increased ubiquitination; when associated with A-861. 1 Publication | 1 | |
Mutagenesisi | 861 | K → A: Decreased sumoylation followed by increased ubiquitination; when associated with A-858. 1 Publication | 1 |
Keywords - Diseasei
Tumor suppressorChemistry databases
ChEMBLi | CHEMBL4295996 |
PTM / Processingi
Molecule processing
Feature key | Position(s) | DescriptionActions | Graphical view | Length |
---|---|---|---|---|
ChainiPRO_0000220889 | 1 – 863 | Axin-1Add BLAST | 863 |
Amino acid modifications
Feature key | Position(s) | DescriptionActions | Graphical view | Length |
---|---|---|---|---|
Modified residuei | 75 | PhosphoserineCombined sources | 1 | |
Modified residuei | 77 | Phosphoserine; by CK1By similarity | 1 | |
Modified residuei | 217 | PhosphoserineCombined sources | 1 | |
Modified residuei | 468 | Phosphoserine; by CK1By similarity | 1 | |
Modified residuei | 480 | Phosphothreonine; by GSK3-beta1 Publication | 1 | |
Modified residuei | 485 | Phosphoserine; by GSK3-beta1 Publication | 1 | |
Modified residuei | 492 | Phosphoserine1 Publication | 1 | |
Modified residuei | 509 | PhosphoserineBy similarity | 1 | |
Cross-linki | 858 | Glycyl lysine isopeptide (Lys-Gly) (interchain with G-Cter in SUMO)2 Publications | ||
Cross-linki | 861 | Glycyl lysine isopeptide (Lys-Gly) (interchain with G-Cter in SUMO)2 Publications |
Post-translational modificationi
Keywords - PTMi
ADP-ribosylation, Isopeptide bond, Phosphoprotein, Ubl conjugationProteomic databases
MaxQBi | O35625 |
PaxDbi | O35625 |
PRIDEi | O35625 |
ProteomicsDBi | 273638 [O35625-1] 273639 [O35625-2] |
PTM databases
iPTMneti | O35625 |
PhosphoSitePlusi | O35625 |
Expressioni
Tissue specificityi
Developmental stagei
Interactioni
Subunit structurei
Homodimer (PubMed:17681137).
Component of the beta-catenin destruction complex, containing at least CTNNB1, an axin and GSK3B, that regulates CTNNB1 protein levels through phosphorylation and ubiquitination (By similarity).
Interacts with GSK3B; the interaction hyperphosphorylates CTNNB1 leading to its ubiquitination and destruction (By similarity).
Interacts with DAXX; the interaction stimulates the interaction of DAXX with TP53, stimulates 'Ser-46' phosphorylation of TP53 and induces cell death on UV irradiation (By similarity).
Also interacts with APC, RNF111, SMAD6 and SMAD7 (By similarity).
Interacts (via the C-terminal) with PPP1CA; the interaction dephosphorylates AXIN1 and regulates interaction with GSK3B (By similarity).
Interacts with PPP2CA; the interaction dephosphorylates AXIN1 (By similarity).
Interacts with MDFI; the interaction decreases AXIN1-mediated JUN N-terminal kinase (JNK) activation (By similarity).
Interacts with MDFIC; the interaction inhibits beta-cateninin-mediated signaling and AXIN1-mediated JUN N-terminal kinase (JNK) activation (By similarity). Binds ANKRD6, PIAS1, PIAS2, PIAS4, SUMO1, MAP3K1 and MAP3K4 (PubMed:12183362, PubMed:12223491).
Component of the AXIN1-HIPK2-TP53 complex (PubMed:15526030).
Interacts directly in the complex with TP53 and HIPK2 (PubMed:15526030).
Interacts with DIXDC1; the interaction prevents interaction with MAP3K1 (PubMed:15262978).
Interacts with AIDA; the interaction blocks the AXIN1-mediated JNK activation through disrupting AXIN1 homodimerization and Wnt signaling (PubMed:17681137).
Interacts with LRP5 (via its phosphorylated PPPSP motifs); the interaction is stimulated by WNT1 and GSK3B and activates beta-catenin signaling (PubMed:11336703).
Interacts with CTNNB1 (via the armadillo repeats 2-7) (PubMed:10581160, PubMed:15063782).
Interacts with MACF1 (By similarity).
Found in a complex composed of MACF1, APC, AXIN1, CTNNB1 and GSK3B (By similarity).
Interacts with TNKS (By similarity).
Interacts with DAB2; the interaction is mutually exclusive with the AXIN1:PPP1CA interaction (PubMed:19581931).
Interacts with ZBED3 (via PPPSP motif); the interaction is direct, enhanced by protein kinase GSK3B and casein kinase CSNK1E activities and decreases GSK3B-induced beta-catenin serine and threonine phosphorylations (PubMed:19141611).
Interacts with WDR26 (By similarity).
Interacts with GID8 (By similarity).
By similarity10 PublicationsBinary interactionsi
Hide detailsO35625
GO - Molecular functioni
- armadillo repeat domain binding Source: MGI
- beta-catenin binding Source: MGI
- enzyme binding Source: MGI
- identical protein binding Source: MGI
- I-SMAD binding Source: BHF-UCL
- p53 binding Source: MGI
- protein C-terminus binding Source: MGI
- protein domain specific binding Source: MGI
- protein homodimerization activity Source: UniProtKB
- protein kinase binding Source: ParkinsonsUK-UCL
- protein self-association Source: MGI
- R-SMAD binding Source: MGI
- signaling receptor binding Source: MGI
- SMAD binding Source: MGI
- ubiquitin protein ligase binding Source: BHF-UCL
Protein-protein interaction databases
BioGRIDi | 198287, 34 interactors |
ComplexPortali | CPX-103, Beta-catenin destruction core complex, variant 1 CPX-448, Beta-catenin destruction core complex, variant 2 CPX-453, Beta-catenin destruction core complex, variant 5 CPX-456, Beta-catenin destruction core complex, variant 6 |
CORUMi | O35625 |
DIPi | DIP-42637N |
ELMi | O35625 |
IntActi | O35625, 29 interactors |
MINTi | O35625 |
STRINGi | 10090.ENSMUSP00000073974 |
Miscellaneous databases
RNActi | O35625, protein |
Structurei
Secondary structure
3D structure databases
SMRi | O35625 |
ModBasei | Search... |
PDBe-KBi | Search... |
Family & Domainsi
Domains and Repeats
Feature key | Position(s) | DescriptionActions | Graphical view | Length |
---|---|---|---|---|
Domaini | 88 – 211 | RGSPROSITE-ProRule annotationAdd BLAST | 124 | |
Domaini | 781 – 863 | DIXPROSITE-ProRule annotationAdd BLAST | 83 |
Region
Feature key | Position(s) | DescriptionActions | Graphical view | Length |
---|---|---|---|---|
Regioni | 209 – 338 | Interaction with TP531 PublicationAdd BLAST | 130 | |
Regioni | 348 – 432 | Interaction with GSK3BBy similarityAdd BLAST | 85 | |
Regioni | 433 – 501 | Interaction with beta-cateninBy similarityAdd BLAST | 69 | |
Regioni | 505 – 758 | Interaction with RNF111By similarityAdd BLAST | 254 | |
Regioni | 572 – 790 | Interaction with PPP2CABy similarityAdd BLAST | 219 | |
Regioni | 678 – 753 | Interaction with HIPK21 PublicationAdd BLAST | 76 |
Motif
Feature key | Position(s) | DescriptionActions | Graphical view | Length |
---|---|---|---|---|
Motifi | 20 – 29 | Tankyrase-binding motif | 10 |
Domaini
Phylogenomic databases
eggNOGi | KOG3589, Eukaryota |
InParanoidi | O35625 |
OrthoDBi | 1481971at2759 |
Family and domain databases
CDDi | cd11582, Axin_TNKS_binding, 1 hit |
DisProti | DP02456 |
Gene3Di | 1.10.196.10, 2 hits 3.10.20.380, 1 hit |
IDEALi | IID50192 |
InterProi | View protein in InterPro IPR043581, Axin-like IPR029797, AXIN1 IPR014936, Axin_b-cat-bd IPR032101, Axin_TNKS-bd IPR001158, DIX IPR038207, DIX_dom_sf IPR016137, RGS IPR036305, RGS_sf IPR024066, RGS_subdom1/3 IPR029071, Ubiquitin-like_domsf |
PANTHERi | PTHR46102, PTHR46102, 1 hit PTHR46102:SF3, PTHR46102:SF3, 1 hit |
Pfami | View protein in Pfam PF16646, AXIN1_TNKS_BD, 1 hit PF08833, Axin_b-cat_bind, 1 hit PF00778, DIX, 1 hit PF00615, RGS, 1 hit |
PRINTSi | PR01301, RGSPROTEIN |
SMARTi | View protein in SMART SM00021, DAX, 1 hit SM00315, RGS, 1 hit |
SUPFAMi | SSF48097, SSF48097, 1 hit SSF54236, SSF54236, 1 hit |
PROSITEi | View protein in PROSITE PS50841, DIX, 1 hit PS50132, RGS, 1 hit |
s (2+)i Sequence
Sequence statusi: Complete.
This entry describes 2 produced by isoformsialternative splicing. AlignAdd to basketThis entry has 2 described isoforms and 3 potential isoforms that are computationally mapped.Show allAlign All
This isoform has been chosen as the sequence. All positional information in this entry refers to it. This is also the sequence that appears in the downloadable versions of the entry. canonicali
10 20 30 40 50
MNVQEQGFPL DLGASFTEDA PRPPVPGEEG ELVSTDSRPV NHSFCSGKGT
60 70 80 90 100
SIKSETSTAT PRRSDLDLGY EPEGSASPTP PYLRWAESLH SLLDDQDGIS
110 120 130 140 150
LFRTFLKQEG CADLLDFWFA CSGFRKLEPC DSNEEKRLKL ARAIYRKYIL
160 170 180 190 200
DSNGIVSRQT KPATKSFIKD CVMKQQIDPA MFDQAQTEIQ STMEENTYPS
210 220 230 240 250
FLKSDIYLEY TRTGSESPKV CSDQSSGSGT GKGMSGYLPT LNEDEEWKCD
260 270 280 290 300
QDADEDDGRD PLPPSRLTQK LLLETAAPRA PSSRRYNEGR ELRYGSWREP
310 320 330 340 350
VNPYYVNSGY ALAPATSAND SEQQSLSSDA DTLSLTDSSV DGIPPYRIRK
360 370 380 390 400
QHRREMQESI QVNGRVPLPH IPRTYRMPKE IRVEPQKFAE ELIHRLEAVQ
410 420 430 440 450
RTREAEEKLE ERLKRVRMEE EGEDGEMPSG PMASHKLPSV PAWHHFPPRY
460 470 480 490 500
VDMGCSGLRD AHEENPESIL DEHVQRVMRT PGCQSPGPGH RSPDSGHVAK
510 520 530 540 550
TAVLGGTASG HGKHVPKLGL KLDTAGLHHH RHVHHHVHHN SARPKEQMEA
560 570 580 590 600
EVARRVQSSF SWGPETHGHA KPRSYSENAG TTLSAGDLAF GGKTSAPSKR
610 620 630 640 650
NTKKAESGKN ANAEVPSTTE DAEKNQKIMQ WIIEGEKEIS RHRKAGHGSS
660 670 680 690 700
GLRKQQAHES SRPLSIERPG AVHPWVSAQL RNSVQPSHLF IQDPTMPPNP
710 720 730 740 750
APNPLTQLEE ARRRLEEEEK RANKLPSKQR YVQAVMQRGR TCVRPACAPV
760 770 780 790 800
LSVVPAVSDL ELSETETKSQ RKAGGGSAPP CDSIVVAYYF CGEPIPYRTL
810 820 830 840 850
VRGRAVTLGQ FKELLTKKGS YRYYFKKVSD EFDCGVVFEE VREDEAVLPV
860
FEEKIIGKVE KVD
Computationally mapped potential isoform sequencesi
There are 3 potential isoforms mapped to this entry.BLASTAlignShow allAdd to basketE9QMJ8 | E9QMJ8_MOUSE | Axin-1 | Axin1 | 868 | Annotation score: | ||
Q14DJ8 | Q14DJ8_MOUSE | Axin-1 | Axin1 | 832 | Annotation score: | ||
F6SKQ8 | F6SKQ8_MOUSE | Axin-1 | Axin1 | 155 | Annotation score: |
Sequence cautioni
Experimental Info
Feature key | Position(s) | DescriptionActions | Graphical view | Length |
---|---|---|---|---|
Sequence conflicti | 589 | A → P in AAC53285 (PubMed:9230313).Curated | 1 | |
Sequence conflicti | 787 | A → G in AAC53285 (PubMed:9230313).Curated | 1 | |
Sequence conflicti | 846 | A → P in AAC53285 (PubMed:9230313).Curated | 1 |
Alternative sequence
Feature key | Position(s) | DescriptionActions | Graphical view | Length |
---|---|---|---|---|
Alternative sequenceiVSP_000452 | 731 – 766 | Missing in isoform 2. 1 PublicationAdd BLAST | 36 |
Sequence databases
Select the link destinations: EMBLi GenBanki DDBJi Links Updated | AF009011 mRNA Translation: AAC53285.1 Different initiation. AC126438 Genomic DNA No translation available. AC140047 Genomic DNA No translation available. |
RefSeqi | NP_033863.2, NM_009733.2 |
Genome annotation databases
GeneIDi | 12005 |
KEGGi | mmu:12005 |
Keywords - Coding sequence diversityi
Alternative splicingSimilar proteinsi
Cross-referencesi
Sequence databases
Select the link destinations: EMBLi GenBanki DDBJi Links Updated | AF009011 mRNA Translation: AAC53285.1 Different initiation. AC126438 Genomic DNA No translation available. AC140047 Genomic DNA No translation available. |
RefSeqi | NP_033863.2, NM_009733.2 |
3D structure databases
Select the link destinations: PDBei RCSB PDBi PDBji Links Updated | PDB entry | Method | Resolution (Å) | Chain | Positions | PDBsum |
3UTM | X-ray | 2.00 | C | 1-80 | [»] | |
SMRi | O35625 | |||||
ModBasei | Search... | |||||
PDBe-KBi | Search... |
Protein-protein interaction databases
BioGRIDi | 198287, 34 interactors |
ComplexPortali | CPX-103, Beta-catenin destruction core complex, variant 1 CPX-448, Beta-catenin destruction core complex, variant 2 CPX-453, Beta-catenin destruction core complex, variant 5 CPX-456, Beta-catenin destruction core complex, variant 6 |
CORUMi | O35625 |
DIPi | DIP-42637N |
ELMi | O35625 |
IntActi | O35625, 29 interactors |
MINTi | O35625 |
STRINGi | 10090.ENSMUSP00000073974 |
Chemistry databases
ChEMBLi | CHEMBL4295996 |
PTM databases
iPTMneti | O35625 |
PhosphoSitePlusi | O35625 |
Proteomic databases
MaxQBi | O35625 |
PaxDbi | O35625 |
PRIDEi | O35625 |
ProteomicsDBi | 273638 [O35625-1] 273639 [O35625-2] |
Genome annotation databases
GeneIDi | 12005 |
KEGGi | mmu:12005 |
Organism-specific databases
CTDi | 8312 |
MGIi | MGI:1096327, Axin1 |
Phylogenomic databases
eggNOGi | KOG3589, Eukaryota |
InParanoidi | O35625 |
OrthoDBi | 1481971at2759 |
Enzyme and pathway databases
Reactomei | R-MMU-195253, Degradation of beta-catenin by the destruction complex R-MMU-196299, Beta-catenin phosphorylation cascade R-MMU-201681, TCF dependent signaling in response to WNT R-MMU-4641257, Degradation of AXIN R-MMU-4641262, Disassembly of the destruction complex and recruitment of AXIN to the membrane R-MMU-5689880, Ub-specific processing proteases |
Miscellaneous databases
BioGRID-ORCSi | 12005, 4 hits in 54 CRISPR screens |
ChiTaRSi | Axin1, mouse |
PROi | PR:O35625 |
RNActi | O35625, protein |
SOURCEi | Search... |
Family and domain databases
CDDi | cd11582, Axin_TNKS_binding, 1 hit |
DisProti | DP02456 |
Gene3Di | 1.10.196.10, 2 hits 3.10.20.380, 1 hit |
IDEALi | IID50192 |
InterProi | View protein in InterPro IPR043581, Axin-like IPR029797, AXIN1 IPR014936, Axin_b-cat-bd IPR032101, Axin_TNKS-bd IPR001158, DIX IPR038207, DIX_dom_sf IPR016137, RGS IPR036305, RGS_sf IPR024066, RGS_subdom1/3 IPR029071, Ubiquitin-like_domsf |
PANTHERi | PTHR46102, PTHR46102, 1 hit PTHR46102:SF3, PTHR46102:SF3, 1 hit |
Pfami | View protein in Pfam PF16646, AXIN1_TNKS_BD, 1 hit PF08833, Axin_b-cat_bind, 1 hit PF00778, DIX, 1 hit PF00615, RGS, 1 hit |
PRINTSi | PR01301, RGSPROTEIN |
SMARTi | View protein in SMART SM00021, DAX, 1 hit SM00315, RGS, 1 hit |
SUPFAMi | SSF48097, SSF48097, 1 hit SSF54236, SSF54236, 1 hit |
PROSITEi | View protein in PROSITE PS50841, DIX, 1 hit PS50132, RGS, 1 hit |
ProtoNeti | Search... |
MobiDBi | Search... |
Entry informationi
Entry namei | AXIN1_MOUSE | |
Accessioni | O35625Primary (citable) accession number: O35625 | |
Entry historyi | Integrated into UniProtKB/Swiss-Prot: | December 1, 2000 |
Last sequence update: | October 3, 2012 | |
Last modified: | April 7, 2021 | |
This is version 198 of the entry and version 3 of the sequence. See complete history. | ||
Entry statusi | Reviewed (UniProtKB/Swiss-Prot) | |
Annotation program | Chordata Protein Annotation Program |
Miscellaneousi
Keywords - Technical termi
3D-structure, Reference proteomeDocuments
- MGD cross-references
Mouse Genome Database (MGD) cross-references in UniProtKB/Swiss-Prot - PDB cross-references
Index of Protein Data Bank (PDB) cross-references