Evolutionary classification of protein domain structures

alpha arraysalpha-helix arrays with mainly perpendicular helices

alpha bundlesalpha-helix bundles with mainly parallel helices

alpha superhelicesrepeating alpha-helix hairpins form a superhelix

X: Bifunctional inhibitor/lipid-transfer protein/seed storage 2S albumin-like

X: Hypothetical protein SF216

X: Indoleamine 2,3-dioxygenase N-terminal subdomain

X: Repetitive alpha hairpins

H: Glutathione S-transferase (GST)-C

H: alpha/alpha toroid

H: Ankyrin repeat

H: Pseudo ankyrin repeat

H: ARM repeat

H: RPAP3 C-terminal domain-like

H: Nuclear pore complex component Nup133/Nup170/Nup157 C-terminal domains

H: adenylylcyclase associated protein, CAP-N

H: Ras GEF

H: Cytochrome c oxidase subunit E

H: Arp2/3 complex 16 KDa subunit ARPC5

H: Hypothetical protein ST1625

H: MgtE N-terminal domain-like

H: TROVE domain-like

H: Translin

H: C-terminal domain of Ku80

H: Proteasome activator BLM10

H: Immunity Factor for SPN

H: Nucleoporin Nup84/Nup107

H: Coatomer subunit alpha C-terminal domain

H: Nucleoporin NUP85/Nucleoporin NUP145 C-terminal domain

H: Survival of motor neuron protein-interacting protein 1

H: C-terminal domain in vacuolar protein sorting-associated protein 54

H: Helical domain in dedicator of cytokinesis protein 9

H: GPCR-autoproteolysis inducing domain subdomain A

H: BACK domain

H: EssB extracellular domain

H: Chloroplast inner membrane protein TIC110

H: Alkylsulfatase SdsA1 linker domain

H: TIR domain-containing adapter molecule 1 N-terminal domain

H: 26S proteasome subunit Rpn2 N-terminal domain

T: 26S proteasome subunit Rpn2 N-terminal domain

F: RPN2_N

PF21505 CL0020

F: RPN1_RPN2_N

PF17781 CL0020

Representatives:

e4cr2Z2[Z:49-365] * nonrep Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S PROTEASOME REGULATORY SUBUNIT RPN1 ; ELECTRON MICROSCOPY

e5gjqZ1[Z:106-356] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e4cr3Z3[Z:49-365] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S PROTEASOME REGULATORY SUBUNIT RPN1 ; ELECTRON MICROSCOPY

e4cr4Z2[Z:49-365] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S PROTEASOME REGULATORY SUBUNIT RPN1 ; ELECTRON MICROSCOPY

e5a5bZ1[Z:49-365] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S PROTEASOME REGULATORY SUBUNIT RPN1 ; ELECTRON MICROSCOPY

e3jcoZ2[Z:99-365] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome regulatory subunit RPN1 ; ELECTRON MICROSCOPY

e3jcpZ2[Z:99-365] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome regulatory subunit RPN1 ; ELECTRON MICROSCOPY

e5gjrZ1[Z:106-356] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e5gjrAC3[AC:106-356] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e5t0gf2[f:1-197] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e5t0hf2[f:1-197] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e5t0if2[f:1-197] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e5t0jf2[f:1-197] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e5t0cAf2[Af:133-134,Af:164-356] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e5t0cBf2[Bf:133-134,Bf:164-356] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e5mpdZ1[Z:1-366] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome regulatory subunit RPN1 ; ELECTRON MICROSCOPY

e5mpcZ2[Z:1-366] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome regulatory subunit RPN1 ; ELECTRON MICROSCOPY

e5wviZ2[Z:49-365] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome regulatory subunit RPN1 ; ELECTRON MICROSCOPY

e5wvkZ3[Z:49-365] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome regulatory subunit RPN1 ; ELECTRON MICROSCOPY

e5ln3Z3[Z:58-356] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e5vhjf2[f:70-103,f:106-356] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e5vhpf2[f:70-103,f:106-356] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e5vhsf1[f:70-103,f:106-356] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e5vhff1[f:6-55,f:58-356] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e5vhhf1[f:6-55,f:58-356] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e5vhif2[f:6-55,f:58-356] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e5vhmf1[f:6-55,f:58-356] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e5vhnf1[f:6-55,f:58-356] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e5vhof1[f:6-55,f:58-356] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e5vhqf1[f:6-55,f:58-356] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e5vhrf1[f:6-55,f:58-356] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e6epcZ1[Z:1-357] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e6epdZ3[Z:1-357] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e6epfZ3[Z:1-357] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e5vfpf2[f:6-356] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e5vfqf2[f:6-356] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e5vfrf2[f:6-356] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e5vfsf1[f:6-356] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e5vftf1[f:6-356] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e5vfuf1[f:6-356] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e6fvuZ1[Z:1-366] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome regulatory subunit RPN1 ; ELECTRON MICROSCOPY

e6fvvZ1[Z:1-366] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome regulatory subunit RPN1 ; ELECTRON MICROSCOPY

e6fvxZ2[Z:1-366] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome regulatory subunit RPN1 ; ELECTRON MICROSCOPY

e6fvyZ3[Z:1-366] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome regulatory subunit RPN1 ; ELECTRON MICROSCOPY

e6msef2[f:1-357] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e6msgf1[f:1-357] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e6mshf2[f:4-357] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e6msjf3[f:1-357] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e6mskf2[f:1-357] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e6msbf2[f:1-357] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e6msdf3[f:1-357] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e6j2cZ2[Z:49-365] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome regulatory subunit RPN1 ; ELECTRON MICROSCOPY

e6j2qZ3[Z:49-365] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome regulatory subunit RPN1 ; ELECTRON MICROSCOPY

e6j2xZ3[Z:49-365] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome regulatory subunit RPN1 ; ELECTRON MICROSCOPY

e6j2nZ2[Z:49-365] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome regulatory subunit RPN1 ; ELECTRON MICROSCOPY

e6j30Z2[Z:49-365] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome regulatory subunit RPN1 ; ELECTRON MICROSCOPY

e5mpbZ2[Z:1-366] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome regulatory subunit RPN1 ; ELECTRON MICROSCOPY

e5mpeZ2[Z:1-366] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome regulatory subunit RPN1 ; ELECTRON MICROSCOPY

e5l4kZ3[Z:1-357] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e6fvtZ1[Z:1-366] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome regulatory subunit RPN1 ; ELECTRON MICROSCOPY

e6fvwZ1[Z:1-366] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome regulatory subunit RPN1 ; ELECTRON MICROSCOPY

e6wjdf1[f:1-357] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e6wjnf1[f:6-356] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e7qo5Z2[Z:1-366] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome regulatory subunit RPN1 ; ELECTRON MICROSCOPY

e7qo3Z2[Z:1-366] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome regulatory subunit RPN1 ; ELECTRON MICROSCOPY

e7qo4Z1[Z:1-366] Image Pymol Jmol Links: PDB, SCOP, CATH DOI

26S proteasome regulatory subunit RPN1 ; ELECTRON MICROSCOPY

e7qo6Z1[Z:1-366] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome regulatory subunit RPN1 ; ELECTRON MICROSCOPY

e7w37f2[f:1-357] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e7w38f2[f:1-357] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e7w39f1[f:1-357] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e7w3af1[f:1-357] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e7w3bf1[f:1-357] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e7w3cf2[f:1-357] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e7w3ff2[f:1-357] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e7w3gf2[f:1-357] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e7w3hf2[f:1-357] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e7w3if1[f:1-357] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e7w3jf1[f:1-357] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e7w3kf1[f:1-357] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e7w3mf2[f:1-357] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e8amzZ1[Z:42-358] Image Pymol Jmol Links: PDB, SCOP, CATH

26S proteasome non-ATPase regulatory subunit 2 homolog ; ELECTRON MICROSCOPY

e8cvtf1[f:6-356] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e7qy7f2[f:6-356] Image Pymol Jmol Links: PDB, SCOP, CATH

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e7qyaf2[f:6-356] Image Pymol Jmol Links: PDB, SCOP, CATH

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e7qxnf1[f:1-357] Image Pymol Jmol Links: PDB, SCOP, CATH

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e7qxpf1[f:1-357] Image Pymol Jmol Links: PDB, SCOP, CATH

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e7qxuf1[f:1-357] Image Pymol Jmol Links: PDB, SCOP, CATH

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e7qxwf1[f:1-357] Image Pymol Jmol Links: PDB, SCOP, CATH

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e7qxxf1[f:1-357] Image Pymol Jmol Links: PDB, SCOP, CATH

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

e7qybf1[f:1-357] Image Pymol Jmol Links: PDB, SCOP, CATH

26S proteasome non-ATPase regulatory subunit 2 ; ELECTRON MICROSCOPY

H: Proteasome/cyclosome (PC) repeat

H: Protein transport protein SEC39

H: Anion channel SLAC1-related

H: Telomere length regulation protein TEL2

H: transcription anti-terminator antagonist UpxZ

H: DNA polymerase alpha-binding protein Ctf4 C-terminal domain

H: Ribosomal protein S12 methylthiotransferase accessory factor YcaO C-terminal domain

H: E3 ubiquitin-protein ligase SHPRH first helical domain

H: Helical insertion in sensor domain of histidine kinase VC_A0565

H: Anaphase-promoting complex subunit 1 first helical domain

H: Anaphase-promoting complex subunit 1 second helical domain

H: Helical domain in TOPLESS related protein 2 (TPR2)

H: Helical C-terminal domain in magnesium chelatase catalytic subunit

H: Taz1 helical domain

H: Helical domain in acetyl-CoA carboxylase

H: Pre-mRNA-splicing factor 38A

H: TssA helical domains

H: FRIGIDA flowering-time regulator

H: Peptidoglycan deacetylase Bd3279 N-terminal domain

H: C-terminal tetramerization domain of Utp1/Utp21/Utp12/Utp13

H: Immunity protein CdiI

H: Uncharacterized protein LPG1670

H: Sterol regulatory element-binding protein 1 (Sre1) C-terminal domain

H: DNA repair protein Rev1 C-terminal domain

H: Uncharacterized protein PF2048.1

H: Intraflagellar transport protein 80 (IFT80) C-terminal domain

H: AFF4 C-terminal homology domain

X: C-terminal domain of SidJ

X: N-terminal domain of P-granule protein

X: Cdc45-Binding Domain in Sld3/Treslin

X: Putative 3-oxoacyl-(acyl-carrier-protein) synthase N-terminal domain

X: Helical domain in conserved hypothetical protein Rv3899c

X: RidL repeats

X: Mitochondrial malonyl-CoA decarboxylase helical domain

X: Apoptotic protease-activating factor 1 (Apaf-1) helical domain

X: UL37 N-terminal half

X: Taf5 N-terminal domain-like

X: Cytochrome c oxidase subunit I-like

X: C-terminal domain of alpha and beta subunits of F1 ATP synthase

X: 1-deoxy-D-xylulose-5-phosphate reductoisomerase-C

X: BH3980-like

X: alpha-helical domain in siroheme synthase middle domains-like

X: Peptide N-methyltransferase C-terminal helical domain

X: Alpha-helical domain in virulence-associated V antigen

X: Middle domain of Hypothetical protein MPN330

X: NLRC4 helical domain HD2

X: Mitochondrial mTERF-like

X: Effector protein SidK

X: Surface cell antigen Sca2 helical repeats

X: N-terminal fragment of dynein heavy chain

X: Linker domain of cytoplasmic dynein heavy chain

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