Evolutionary classification of protein domain structures

alpha arraysalpha-helix arrays with mainly perpendicular helices

X: Acanthaporin

X: Protein 2b

X: Aminoglycoside adenyltransferase AadA C-terminal domain

X: IcmW

X: Peptidase inhibitors family I29

X: CRISPR-associated endonuclease Cpf1 PI (PAM-interacting) domain

X: Cas5fv helical domain

X: ICP4 DNA-binding domain

X: Enhancer of polycomb-like protein 1 (Epl1) N-terminal domain

X: RDS3 complex subunit 10

X: Oxalate biosynthetic component 1 (Obc1) cap domain

X: Glycosyl transferase TarS linker domain

X: Immunomodulating metalloprotease IMPa helical domain

X: Mimivirus sulfhydryl oxidase R596 ORFan domain

X: SOCS box-like

X: Dcp2 box A domain

X: BH2638-like

X: Hypothetical protein YqbG-like

X: EF2947-like

X: Monopolin complex subunit MAM1

X: Csd1/Csd2 helical domain

X: RbcX-like

X: Melanoregulin

X: SP0561-like

X: Phage replication organizer domain

X: DdrO C-terminal domain

X: beta-catenin-interacting protein ICAT

X: Eukaryotic initiation factor 4f subunit eIF4g, eIF4e-binding domain

X: HAND domain of the nucleosome remodeling ATPase ISWI

X: KRAB domain (Kruppel-associated box, Pfam 01352)

X: N-terminal, cytoplasmic domain of anti-sigma factors

X: Replisome organizer (g39p helicase loader/inhibitor protein)

X: TAF(II)230 TBP-binding fragment

X: CRIB domain

X: Nuclear receptor coactivator CBP/p300 ibid domain

X: Nuclear receptor coactivator ACTR

X: Triger factor/SurA peptide-binding domain-like

X: BSD domain

X: Toxin A (TcdA) helical domain

X: Enzyme I of the PEP:sugar phosphotransferase system HPr-binding (sub)domain

X: Hepatitis B viral capsid (hbcag)

X: Pre-protein crosslinking domain of SecA

X: Tetrahydrodipicolinate-N-succinlytransferase, N-terminal 3-helical domain

X: VHP, Villin headpiece domain

X: Chemotaxis receptor methyltransferase CheR, N-terminal domain

X: Chemosensory protein Csp2

X: a domain of protein A6KY75

X: Kinetoplastid membrane protein 11

X: Domains of FliG

X: Type III secretion system domain-like

X: Quinohemoprotein amine dehydrogenase C chain

X: Ribosomal protein L19 (L19e) N-terminal domain

X: HMG-box

X: C-terminus of TFIIE alpha

X: PABP domain-like

X: Zinc transporter ZIP4 N-terminal domain

X: SPP1 phage GP23.1

X: KorB C-terminal domain-like

X: Middle domain in transcriptional anti-activator ExsD

X: Negative regulator RsdA N-terminal domain

X: RNA polymerase sigma factor rpoD N-terminal domain

X: Myosin-binding motif (m-domain) C-terminal subdomain

X: Mitochondrial 54S ribosomal protein L2

X: Small, acid-soluble spore protein C

X: HTH

X: C-terminal domain of Malic enzyme

X: Twin-arginine translocation pathway signal

X: S15/NS1 RNA-binding domain

X: Glycogen debranching enzyme (GDE) insertion domain

X: Dimerization domain of Sgt2

X: RPB6/omega subunit-like

X: helical bundle in Bacillus stearothermophilus-like DNA polymerase I

X: inserted helical bundle subdomain in T7 RNA polymerase

X: Eukaryotic translation initiation factor 3 subunit 1

X: Staphylococcal peroxidase inhibitor

X: Catalytic cysteine domain in ubiquitin-activating enzyme

X: HHA-like

X: Methane monooxygenase hydrolase gamma subunit-like

X: T4 Bacteriophage Helicase Uvsw.1

X: Helical bundle domain in YebC-like proteins

X: Alpha-helical domain in eukaryotic DNA topoisomerase I, N-terminal DNA-binding fragment

X: Superantigen MAM C-terminal domain

X: Emsy N terminal (ENT) domain-like

X: RPA2825-like

X: TerB-like

X: C-terminal domain of Hypothetical protein MPN330-like

X: SHQ1 C-terminal domain-like

X: C-terminal helical domain in Atu1540-like proteins

X: BART

X: Asl3597

X: Helical box domain of E3 ubiquitin-protein ligase HECW1

X: HopAB effectors Pto-binding domain-related

X: RNA polymerase-associated protein Gp33

X: Intramolecular chaperone domain in virus tail spike protein

X: Golgi phosphoprotein 3

X: Uncharacterized protein BVU_3817 C-terminal domain

X: Rap1 C-terminal domain

X: N-terminal domain in putative methyltransferase PG_1098

X: N-terminal domain in MogR repressor

X: Thymine dioxygenase JBP1 DNA-binding domain-like

X: RecQL4 helicase N-terminal domain

X: Uncharacterized protein encoded by cryptic prophage

X: Peroxisomal biogenesis factor 14 N-terminal domain

X: Pfam family PF09836 C-terminal domain

X: Pfam family PF09836 N-terminal domain

X: HSDR subunit helical domain

X: beta-herpesvirus envelope glycoprotein L (gL) N-terminal domain

X: Uncharacterized protein AF_2093 N-terminal domain

X: T4 RNA ligase

X: Dimerization domain in caprin-1 and PAN3

X: C-terminal domain of Lmo2642 protein

X: Iron-regulated surface determinant protein H linker domain

X: Helical domain in PB2

X: Uncharacterized protein aq_1974

X: 60S acidic ribosomal protein P1/P2

X: Cell-shape determining Csd6 N-terminal dimerization domain

X: Protelomerase stirrup domain

X: DNA repair protein RAD4 beta-hairpin domain

X: DUF3349

X: Virus VPg protein

X: Macrodomain Ter protein MatP

X: Nucleophosmin DNA-binding domain

X: HhH/H2TH

X: DNA polymerase III finger domain

X: Insertion domain of glycoside hydrolase family 149 (GH149)

X: Insertion region of FTHFS domain

X: Antitermination protein Q helical domain

X: Nitrogenase gamma subunit N-terminal domain

X: N-terminal helical domain in Poxvirus poly(A) polymerase catalytic subunit

X: lambda integrase-N-like

X: uncharacterized protein BT_1490 C-terminal domain

X: Protelomerase muzzle domain

X: Helical bundle domain in elongation factor 3A

X: Helical insertion domain in magnesium chelatase catalytic subunit

X: Nogo-66

X: Filamentous archaeal viruses coat proteins

X: N-terminal domain of N-acetylglucosaminyltransferase-V

X: Protein C'

X: Helical domain in 5'->3' exoribonucleases

X: DNA-binding domain in UvrA

X: MRG domain

X: PWI domain-like

X: L-aspartase middle domain-like

X: L-aspartase N-terminal domain-like

X: L-aspartase C-terminal domain-like

X: Protein arginine N-methyltransferase 3 helical domain

X: RuvA-C

X: AvrRxo1-ORF2

X: DnaD domain

X: Primosome protein DnaB middle domain

X: PG0816-like

X: Capsid assembly protein VP3

X: Hypothetical protein MTH393

X: Repressor activator protein 1 (RAP1) helical bundle domain

X: YAP1 redox domain

X: Peripheral subunit-binding domain of 2-oxo acid dehydrogenase complex

X: Alpha helical domain of ribonucleotide reductases

X: Fertilization protein

X: LEM/SAP HeH motif-like

X: attachment domain of fiber adhesin

X: DNA-binding domain of EIN3-like

X: DNA polymerase III theta subunit-like

X: inserted helical subdomain in bacterial RNA-polymerase beta-prime subunit

X: Porin B (PorB)

X: Bromodomain-containing protein 4 ET domain

X: PHAX RNA-binding domain

X: SP1917-like

X: MJ1004, C-terminal domain

X: MshE c-di-GMP-binding domain

X: tRNA delta(2)-isopentenylpyrophosphate transferase helical insertion domain

X: Potassium-transporting ATPase KdpC subunit

X: EF-hand

X: Jann4075-like

X: PBS linker domain of phycobilisome linker polypeptide

X: C-terminal helical domain in tRNA modifying enzyme GidA

X: Calcium binding protein 40 (CBP40) N-terminal domain

X: Neutral trehalase N-terminal domain

X: Uteroglobin-like

X: Uncharacterized protein CD1104.2

X: Annexin

X: Guanido kinase-N

X: Repressor of bacterial conjugation FinO

X: DnaB helicase N-terminal domain-related

X: Transcription factor STAT-4 N-domain

X: N-terminal domain of segregation and condensation protein A, ScpA

X: YgfY-like (DUP399, Pfam03937)

X: Orange carotenoid protein, N-terminal domain

X: AhpD-like

X: KaiA/RbsU domain-like

X: YoaC-like

X: WY-domain in RXLR effectors

X: ATR1 N-terminal domain

X: Serum amyloid A-1 protein

X: Methionine synthase domain-like

X: Protein of Unknown Function YPO2564

X: Hypothetical protein

X: Serine acetyltransferase N-terminal domain

X: Nucleoside phosphorylase/phosphoribosyltransferase-N

X: yeast protein YOR252W

X: HP0721

X: ERP29 C domain-like

X: C-terminal alpha domain in Alpha-Glycerophosphate Oxidase

X: Uncharacterized protein CV_1783

X: D-ornithine aminomutase S component-related

X: Non-structural protein 3

X: Retroviral matrix proteins

X: T4 endonuclease V

X: Insertion subdomain in DsbA-like

X: Insert all-alpha domain in prim-pol

X: Calcium-binding protein

X: Archaeal protein SSO6904

X: Saposin-like

X: Cytoplasmic metal binding domain of VIT1

X: Globin-like

X: N-terminal domain of viral protein A26

X: Uncharacterized protein ABAYE3142

X: Toxins' membrane translocation domains

X: BID domain of Bartonella effector protein (Bep)

X: AopB

X: Phospholipid translocation channel MlaA

X: RNA-binding domain of telomerase

X: Presenilin family intramembrane aspartate proteases

X: alpha-helical ferredoxin-like

H: alpha-helical ferredoxin

T: alpha-helical ferredoxin

F: Fer4_10

PF13237 CL0344

Representatives:

e1kf6B1[B:106-243] nonrep Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

FUMARATE REDUCTASE IRON-SULFUR PROTEIN ; ligands: CE1,F3S,HQO,SF4 ; X-RAY DIFFRACTION 2.7Å

e1kf6N1[N:106-243] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

FUMARATE REDUCTASE IRON-SULFUR PROTEIN ; ligands: F3S,HQO,SF4 ; X-RAY DIFFRACTION 2.7Å

e1kfyB1[B:106-243] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

FUMARATE REDUCTASE IRON-SULFUR PROTEIN ; ligands: BRS,CE1,F3S,SF4 ; X-RAY DIFFRACTION 3.6Å

e1kfyN1[N:106-243] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

FUMARATE REDUCTASE IRON-SULFUR PROTEIN ; ligands: BRS,F3S,SF4 ; X-RAY DIFFRACTION 3.6Å

e1l0vB1[B:106-243] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

FUMARATE REDUCTASE IRON-SULFUR PROTEIN ; ligands: CE1,F3S,MQ7,SF4 ; X-RAY DIFFRACTION 3.3Å

e1l0vN1[N:106-243] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

FUMARATE REDUCTASE IRON-SULFUR PROTEIN ; ligands: F3S,MQ7,SF4 ; X-RAY DIFFRACTION 3.3Å

e2b76B1[B:106-243] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Fumarate reductase iron-sulfur protein ; ligands: F3S,SF4 ; X-RAY DIFFRACTION 3.3Å

e2b76N1[N:106-243] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Fumarate reductase iron-sulfur protein ; ligands: F3S,SF4 ; X-RAY DIFFRACTION 3.3Å

e3cirB1[B:106-243] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Fumarate reductase iron-sulfur subunit ; ligands: F3S,SF4 ; X-RAY DIFFRACTION 3.65Å

e3cirN1[N:106-243] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Fumarate reductase iron-sulfur subunit ; ligands: F3S,SF4 ; X-RAY DIFFRACTION 3.65Å

e3p4pB1[B:106-243] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Fumarate reductase iron-sulfur protein ; ligands: F3S,SF4 ; X-RAY DIFFRACTION 2.8Å

e3p4pN1[N:106-243] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Fumarate reductase iron-sulfur protein ; ligands: F3S,SF4 ; X-RAY DIFFRACTION 2.8Å

e3p4qB1[B:106-243] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

FUMARATE REDUCTASE IRON-SULFUR PROTEIN ; ligands: F3S,SF4 ; X-RAY DIFFRACTION 3.35Å

e3p4qN1[N:106-243] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

FUMARATE REDUCTASE IRON-SULFUR PROTEIN ; ligands: F3S,SF4 ; X-RAY DIFFRACTION 3.35Å

e3p4rB1[B:106-243] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Fumarate reductase iron-sulfur subunit ; ligands: F3S,SF4 ; X-RAY DIFFRACTION 2.700Å

e3p4rN1[N:106-243] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Fumarate reductase iron-sulfur subunit ; ligands: F3S,SF4 ; X-RAY DIFFRACTION 2.700Å

e3p4sB1[B:106-243] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Fumarate reductase iron-sulfur subunit ; ligands: F3S,SF4 ; X-RAY DIFFRACTION 3.1Å

e3p4sN1[N:106-243] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Fumarate reductase iron-sulfur subunit ; ligands: F3S,SF4 ; X-RAY DIFFRACTION 3.1Å

e4kx6B1[B:106-243] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Fumarate reductase (Anaerobic), Fe-S subunit ; ligands: F3S,MQ7,SF4 ; X-RAY DIFFRACTION 2.95Å

e4kx6N1[N:106-243] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Fumarate reductase (Anaerobic), Fe-S subunit ; ligands: F3S,MQ7,SF4 ; X-RAY DIFFRACTION 2.95Å

e5vpnB2[B:106-243] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Fumarate reductase iron-sulfur subunit ; ligands: F3S,SF4 ; X-RAY DIFFRACTION 4.22Å

e5vpnF2[F:106-243] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Fumarate reductase iron-sulfur subunit ; ligands: F3S,SF4 ; X-RAY DIFFRACTION 4.22Å

e6awfB1[B:106-241] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Fumarate reductase iron-sulfur subunit ; ligands: F3S,SF4 ; X-RAY DIFFRACTION 3.35Å

e6awfF1[F:106-240] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Fumarate reductase iron-sulfur subunit ; ligands: F3S,SF4 ; X-RAY DIFFRACTION 3.35Å

e6lumB2[B:133-260] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Succinate dehydrogenase subunit B ; ligands: F3S,HEM,PEV,SF4 ; ELECTRON MICROSCOPY

e6lumK2[K:133-260] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Succinate dehydrogenase subunit B ; ligands: F3S,HEM,PEV,SF4 ; ELECTRON MICROSCOPY

e6lumQ1[Q:133-260] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Succinate dehydrogenase subunit B ; ligands: F3S,HEM,PEV,SF4 ; ELECTRON MICROSCOPY

F: Fer4_20

F: Fer4_17

F: Fer4_8

F: Fer4_9

F: Unmapped domains

Pseudo group of domains that do not map to PFam family profiles. Domains inside should not be considered as in one family.

H: Hypothetical protein HPAG1_0444 helical domain

X: 4Fe-4S binding domain in Dna2

X: Magnetochrome domain

X: Cytochrome c-like

X: DEATH domain

X: RUN domain

X: Helical domain in PH0156-like proteins

X: Helical domain in class 2 OLD protein

X: C-terminal domain of DEAH helicase DHX37

X: C-terminal domain of hRpn13

X: C-terminal helical domain of proline 3-hydroxylase

X: Uncharacterized protein

X: Legumain prodomain

X: PB2 '627' domain-related

X: OrfY

X: DNA polymerase III clamp loader subunits, C-terminal domain

X: Helical domain in Orf11

X: PGBD-like

X: Uncharacterized protein yihD

X: Uncharacterized protein VV2_0175

X: F-box domain

X: Histone-like

X: Activation-binding domain of RNA polymerase II mediator

X: IcmS

X: Heterogeneous nuclear ribonucleoprotein Q acidic domain

X: Origin recognition complex subunit 3 helical insert domain

X: SidC C-terminal domain

X: Ribosomal protein S7

X: Dipeptidyl-peptidase 2 helical domain

X: N-terminal domain in some Dicers

X: RNase III catalytic domain-like

X: CdiA C-terminal nuclease domain

X: Giardia Dicer helical domain bridging RNase IIIa and RNase IIIb

X: SWIB/MDM2 domain

X: Hypothetical protein At3g22680

X: Hypothetical protein MG354

X: Invasion protein A (SipA) , C-terminal actin binding domain

X: LigA subunit of an aromatic-ring-opening dioxygenase LigAB

X: Scaffolding protein gpD of bacteriophage procapsid

X: YcfC-like

X: Glycolipid transfer protein, GLTP

X: YgfB-like

X: SopE-like GEF domain

X: SopD C-terminal domain

X: Di-copper centre-containing domain

X: Cytochrome P450

X: Nuclear receptor ligand-binding domain

X: 6-phosphogluconate dehydrogenase C-terminal domain-like

X: Ribonuclease 3 N-terminal domain

X: Bacterial chaperone lipoprotein (PulS_OutS)

X: Mitochondrial calcium uniporter (MCU)

X: Transducin (alpha subunit), insertion domain

X: Helical insertion of YcjX stress protein

X: helical domain in Api92-like proteins

X: Sec7 domain

X: Ypt/Rab-GAP domain of gyp1p-like

X: helical domain in flagellar biosynthesis protein flhA

X: BEACH domain

X: BRCA2 helical domain

X: Variable surface antigen VlsE

X: alpha-helical domain in 2-methylcitrate dehydratase PrpD

X: Alpha-helical domain in membrane penetration protein mu1

X: Lipase chaperone LifO-like

X: Phosphoprotein C-terminal domain

X: Jann2411-like

X: ATP12-like

X: lvD/EDD N-terminal domain-like

X: FtsH protease domain-like

X: AGR C 984p-like

X: PTPA-like

X: GUN4-like

X: Rv1873-like

X: C-terminal domain in hypothetical protein lpg2210

X: UraD-like

X: Sec63 N-terminal subdomain-like

X: MG296-like

X: YfbU-like, C-terminal subdomain

X: Acyl-CoA dehydrogenase N-terminal domain-like

X: 14 kDa protein of cytochrome bc1 complex (Ubiquinol-cytochrome c reductase)

X: C-terminal helical domain of RNA helicase

X: ORF12 from Lactococcus lactis phage p2

X: Putative triphosphoribosyl-dephospho-coA synthase

X: Uncharacterized protein CV0237

X: Uncharacterized protein yqbN

X: 60S ribosomal protein rpL36 (L36e)

X: Viral structural protein 5

X: Novel E3 ligase (NEL)

X: Coronavirus main proteinase (3Cl-pro, putative coronavirus nsp2) C-terminal domain

X: C-terminal domain of the type III effector Xcv3220 (XopL)

X: Protein Wnt-8

X: C-terminal domains of CstF-64

X: Lettuce necrotic yellow virus phosphoprotein C-terminal domain

X: Flax-rust effector AvrM

X: DP domain

X: DNA mimic protein DMP19

X: Matrix protein 2-1 core domain

X: Virion protein UL25

X: Unknown function protein VPA0580

X: RNA silencing suppressor p21 C-terminal domain

X: Pilus-presented adhesin helical insertion domain

X: Phosphoinositide phosphatase insertion helical domain

X: Phosphoinositide phosphatase C-terminal helical domain

X: Hsc70-interacting protein dimerization domain

X: CCM3/GCKIII dimerization domain

X: Insertion domain in lpg1103-like

X: Phosphomannose isomerase helical insertion domain

X: Histone RNA hairpin-binding protein RNA-binding domain

X: Nitrile hydratase subunit beta N-termial domain

X: Hsp90 co-chaperone CDC37 middle domain

X: Hsp90 co-chaperone CDC37 C-terminal domain

X: F420-reducing hydrogenase subunit beta

X: Nucleoporin NUP120 helical domain

X: Poly(ADP-ribose) glycohydrolase helical domain

X: EDS1-PAD4 (EP) domain

X: SidM Rab1-activation domain

X: Phosphodiesterase 4 upstream conserved regions (UCR)

X: Sir2 N-terminal domain

X: N-terminal helical domain in restriction-modification system methylation subunit-like

X: Nitrogenase vanadium-iron protein delta chain

X: Transmembrane domain of envelope protein E

X: Host-nuclease inhibitor protein Gam

X: C-terminal 4Fe-4S binding domain of ribosomal protein S2-related protein

X: Yst0336-like

X: Helical domain in EC869 CdiA

X: C-terminal domain of Dbr1

X: N-terminal domain of lytM

X: C-terminal domain of Npl4

X: C-terminal domain of Hit1

X: Uncharacterized protein lpg1960

X: inserted region in the C-terminal domain of the archeal LeuRS

X: N-terminal domain of hexon-associated protein (IIIa)

X: N-terminal domain of large tumor antigen

X: Protein A6 N-terminal domain

X: Assembly domain of GTP-binding protein

X: ELMO domain

X: C-terminal domain of USP25

X: GPI-anchored protein

X: Replicase polyprotein 1a N-terminal helical domain

X: AnkH, cap domain

alpha bundlesalpha-helix bundles with mainly parallel helices

alpha superhelicesrepeating alpha-helix hairpins form a superhelix

alpha duplicates or obligate multimersalpha duplicates or monomers associate together to form a compact domain

alpha complex topologyalpha domain with complex and unique topology that cannot be described as array or bundle or superhelix

beta barrelssingle beta-sheet folded upon itself to form a barrel

beta meanderssingle beta-sheet with mainly meander topology

beta sandwichestwo beta-sheets stacked together to form a sandwich

beta duplicates or obligate multimersbeta duplicates or monomers associate together to form a compact domain

beta complex topologybeta domains with complex and unique topology that cannot be described as barrel or sandwich or meander

a+b two layersone alpha-helix layer and one beta-sheet layer

a+b three layersone mainly antiparallel beta-sheet layer sandwiched between two alpha-helix layers

a+b four layerstwo beta-sheet layers sandwiched between two alpha-helix layers

a+b complex topologyalpha and beta domain with complex and unique topology that cannot be described in layers

a+b duplicates or obligate multimersalpha and beta duplicates or monomers associated together to form a compact domain

a/b barrelsrepeating beta-alpha units form a barrel

a/b three-layered sandwichesrepeating beta-alpha units form a sandwich with a mainly parallel beta-sheet layer stacked between two alpha-helix layers

mixed a+b and a/balpha and beta domain consists of both a+b and a/b regions

few secondary structure elementsstabilized by cofactors or disulfides

extended segmentsextended, non-globular segments, frequently bind to other proteins to form complexes

special