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X - Possible homology level

H - Homology level

T - Topology level

F - Family level

* - Provisional representative

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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

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

X: cradle loop barrel

Refs: Structure 14, 1489-1498; Current opinion in structural biology 18, 358-365

H: RIFT-related
T: acid protease

126354, 3-crossover-4

T: double psi

152436, 2-crossover-3, 5-crossover-6

T: AbrB

122'1'344'3', 2-crossover-3, 2'-crossover-3'

T: Bacterial fluorinating enzyme-C

1265437, 2-crossover-3, 6-crossover-7

T: FMN-binding split barrel

123654, 3-crossover-4

T: Surface presentation of antigens (SPOA)

123654, 3-crossover-4, swapping

T: Alanine racemase-C

125436, 2-crossover-3, 5-crossover-6

T: Aminomethyltransferase beta-barrel domain

143256, 1-crossover-2, 4-crossover-5

T: PUA domain

12543, 2-crossover-3

F: LON_substr_bdg

PF02190 CL0178

Representatives:

e2aneA1[A:8-117] nonrep Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

ATP-dependent protease La ; X-RAY DIFFRACTION 2.03Å

e8ojhB2[B:44-339] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

; ligands: EDO,ZN ; X-RAY DIFFRACTION 2.720Å

e2aneH1[H:8-116] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

ATP-dependent protease La ; X-RAY DIFFRACTION 2.03Å

e2aneD1[D:8-117] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

ATP-dependent protease La ; X-RAY DIFFRACTION 2.03Å

e2aneG1[G:8-117] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

ATP-dependent protease La ; X-RAY DIFFRACTION 2.03Å

e2aneB1[B:10-117] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

ATP-dependent protease La ; X-RAY DIFFRACTION 2.03Å

e2aneC1[C:10-117] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

ATP-dependent protease La ; X-RAY DIFFRACTION 2.03Å

e2aneF1[F:8-117] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

ATP-dependent protease La ; X-RAY DIFFRACTION 2.03Å

e2aneE1[E:8-117] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

ATP-dependent protease La ; X-RAY DIFFRACTION 2.03Å

e1zboB1[B:2-198] Image Pymol Jmol Links: PDB, SCOP, CATH

hypothetical protein BPP1347 ; X-RAY DIFFRACTION 2.6Å

e3ljcA1[A:7-245] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

ATP-dependent protease La ; X-RAY DIFFRACTION 2.6Å

e4ci2B1[B:47-309] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

PROTEIN CEREBLON ; X-RAY DIFFRACTION 2.95Å

e4ci3B1[B:47-309] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

PROTEIN CEREBLON ; X-RAY DIFFRACTION 3.50Å

e5hxbZ1[Z:48-319] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Protein cereblon ; X-RAY DIFFRACTION 3.600Å

e5hxbC2[C:48-319] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Protein cereblon ; X-RAY DIFFRACTION 3.600Å

e5v3oC2[C:47-319] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Protein cereblon ; X-RAY DIFFRACTION 3.2Å

e6bn7B1[B:44-319] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Protein cereblon ; X-RAY DIFFRACTION 3.49Å

e6bnbB1[B:64-319] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Protein cereblon ; X-RAY DIFFRACTION 6.34Å

e6bn9B1[B:44-319] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Protein cereblon ; X-RAY DIFFRACTION 4.38Å

e6boyB2[B:44-319] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Protein cereblon ; X-RAY DIFFRACTION 3.33Å

e6bn8B2[B:44-319] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Protein cereblon ; X-RAY DIFFRACTION 3.99Å

e6h0gB2[B:42-319] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Protein cereblon ; X-RAY DIFFRACTION 4.170Å

e6h0fB1[B:69-319] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Protein cereblon ; X-RAY DIFFRACTION 3.250Å

e6h0fE1[E:69-319] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Protein cereblon ; X-RAY DIFFRACTION 3.250Å

e6h0fH2[H:69-319] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Protein cereblon ; X-RAY DIFFRACTION 3.250Å

e6h0fK1[K:69-319] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Protein cereblon ; X-RAY DIFFRACTION 3.250Å

e6h0gE1[E:42-319] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Protein cereblon ; X-RAY DIFFRACTION 4.170Å

e6ihgA1[A:5-190] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon protease ; X-RAY DIFFRACTION 2.397Å

e7cayA1[A:5-172] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

ATP-dependent protease ; X-RAY DIFFRACTION 2.800Å

e7nfyA5[A:123-221,A:272-410] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon protease homolog, mitochondrial ; ELECTRON MICROSCOPY

e7nfyB5[B:123-221,B:272-412] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon protease homolog, mitochondrial ; ELECTRON MICROSCOPY

e7nfyC5[C:123-221,C:272-412] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon protease homolog, mitochondrial ; ELECTRON MICROSCOPY

e7nfyD5[D:123-221,D:272-410] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon protease homolog, mitochondrial ; ELECTRON MICROSCOPY

e7nfyE5[E:123-221,E:272-410] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon protease homolog, mitochondrial ; ELECTRON MICROSCOPY

e7nfyF5[F:123-221,F:272-410] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon protease homolog, mitochondrial ; ELECTRON MICROSCOPY

e7ng4A5[A:123-221,A:272-410] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon protease homolog, mitochondrial ; ELECTRON MICROSCOPY

e7ng4B5[B:123-221,B:272-410] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon protease homolog, mitochondrial ; ELECTRON MICROSCOPY

e7ng4C5[C:123-221,C:272-411] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon protease homolog, mitochondrial ; ELECTRON MICROSCOPY

e7ng4D5[D:123-221,D:272-410] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon protease homolog, mitochondrial ; ELECTRON MICROSCOPY

e7ng4E5[E:123-221,E:272-412] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon protease homolog, mitochondrial ; ELECTRON MICROSCOPY

e7ng4F5[F:123-221,F:272-410] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon protease homolog, mitochondrial ; ELECTRON MICROSCOPY

e7ng5A5[A:123-221,A:272-410] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon protease homolog, mitochondrial ; ELECTRON MICROSCOPY

e7ng5B5[B:123-221,B:272-410] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon protease homolog, mitochondrial ; ELECTRON MICROSCOPY

e7ng5C5[C:123-221,C:272-410] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon protease homolog, mitochondrial ; ELECTRON MICROSCOPY

e7ng5D5[D:123-221,D:272-410] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon protease homolog, mitochondrial ; ELECTRON MICROSCOPY

e7ng5E5[E:123-221,E:272-410] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon protease homolog, mitochondrial ; ELECTRON MICROSCOPY

e7ng5F5[F:123-221,F:272-409] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon protease homolog, mitochondrial ; ELECTRON MICROSCOPY

e6vbkA1[A:1-212] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon211 ; ligands: GOL ; X-RAY DIFFRACTION 1.997Å

e6vbkB1[B:1-210] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon211 ; X-RAY DIFFRACTION 1.997Å

e6xk9Z1[Z:46-339] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Protein cereblon ; ligands: ZN ; X-RAY DIFFRACTION 3.64Å

e6xk9C2[C:47-339] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Protein cereblon ; ligands: ZN ; X-RAY DIFFRACTION 3.64Å

e7ngcA5[A:123-221,A:272-410] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon protease homolog, mitochondrial ; ELECTRON MICROSCOPY

e7ngfA5[A:123-221,A:272-411] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon protease homolog, mitochondrial ; ELECTRON MICROSCOPY

e7ngcB2[B:123-221,B:272-412] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon protease homolog, mitochondrial ; ELECTRON MICROSCOPY

e7ngcC2[C:123-221,C:272-412] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon protease homolog, mitochondrial ; ELECTRON MICROSCOPY

e7ngcD2[D:123-221,D:272-412] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon protease homolog, mitochondrial ; ELECTRON MICROSCOPY

e7ngcE2[E:123-221,E:272-412] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon protease homolog, mitochondrial ; ELECTRON MICROSCOPY

e7ngcF2[F:123-221,F:272-412] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon protease homolog, mitochondrial ; ELECTRON MICROSCOPY

e7ngfB2[B:123-221,B:272-412] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon protease homolog, mitochondrial ; ELECTRON MICROSCOPY

e7ngfC2[C:123-221,C:272-412] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon protease homolog, mitochondrial ; ELECTRON MICROSCOPY

e7ngfD2[D:123-221,D:272-412] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon protease homolog, mitochondrial ; ELECTRON MICROSCOPY

e7ngfE2[E:123-221,E:272-412] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon protease homolog, mitochondrial ; ELECTRON MICROSCOPY

e7ngfF2[F:123-221,F:272-412] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon protease homolog, mitochondrial ; ELECTRON MICROSCOPY

e7nglA2[A:123-221,A:272-412] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon protease homolog, mitochondrial ; ELECTRON MICROSCOPY

e7nglB2[B:123-221,B:272-412] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon protease homolog, mitochondrial ; ELECTRON MICROSCOPY

e7nglC2[C:123-221,C:272-412] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon protease homolog, mitochondrial ; ELECTRON MICROSCOPY

e7nglD2[D:123-221,D:272-412] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon protease homolog, mitochondrial ; ELECTRON MICROSCOPY

e7nglE2[E:123-221,E:272-412] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon protease homolog, mitochondrial ; ELECTRON MICROSCOPY

e7nglF2[F:123-221,F:272-412] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon protease homolog, mitochondrial ; ELECTRON MICROSCOPY

e7ngpA2[A:123-221,A:272-412] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon protease homolog, mitochondrial ; ELECTRON MICROSCOPY

e7ngpB2[B:123-221,B:272-412] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon protease homolog, mitochondrial ; ELECTRON MICROSCOPY

e7ngpC2[C:123-221,C:272-412] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon protease homolog, mitochondrial ; ELECTRON MICROSCOPY

e7ngpD2[D:123-221,D:272-412] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon protease homolog, mitochondrial ; ELECTRON MICROSCOPY

e7ngpE2[E:123-221,E:272-412] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon protease homolog, mitochondrial ; ELECTRON MICROSCOPY

e7ngpF2[F:123-221,F:272-412] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon protease homolog, mitochondrial ; ELECTRON MICROSCOPY

e7ngqA2[A:123-221,A:272-412] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon protease homolog, mitochondrial ; ELECTRON MICROSCOPY

e7ngqB2[B:123-221,B:272-412] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon protease homolog, mitochondrial ; ELECTRON MICROSCOPY

e7ngqC2[C:123-221,C:272-412] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon protease homolog, mitochondrial ; ELECTRON MICROSCOPY

e7ngqD2[D:123-221,D:272-412] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon protease homolog, mitochondrial ; ELECTRON MICROSCOPY

e7ngqE2[E:123-221,E:272-412] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon protease homolog, mitochondrial ; ELECTRON MICROSCOPY

e7ngqF2[F:123-221,F:272-412] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon protease homolog, mitochondrial ; ELECTRON MICROSCOPY

e7craA1[A:-1-210] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon protease ; ligands: SO4 ; X-RAY DIFFRACTION 1.7Å

e7lpsB2[B:47-339] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Protein cereblon ; ligands: RN9,ZN ; X-RAY DIFFRACTION 3.78Å

e7cr9A1[A:0-206] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon protease ; X-RAY DIFFRACTION 2.09Å

e7cr9B1[B:0-206] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon protease ; X-RAY DIFFRACTION 2.09Å

e7lpsE2[E:47-339] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Protein cereblon ; ligands: RN9,ZN ; X-RAY DIFFRACTION 3.78Å

e7lpsH2[H:47-339] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Protein cereblon ; ligands: RN9,ZN ; X-RAY DIFFRACTION 3.78Å

e7lpsK2[K:47-339] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Protein cereblon ; ligands: RN9,ZN ; X-RAY DIFFRACTION 3.78Å

e7oxoA2[A:123-221,A:272-412] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon protease homolog, mitochondrial ; ELECTRON MICROSCOPY

e7oxoB2[B:123-221,B:272-412] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon protease homolog, mitochondrial ; ELECTRON MICROSCOPY

e7oxoC2[C:123-221,C:272-412] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon protease homolog, mitochondrial ; ELECTRON MICROSCOPY

e7oxoD2[D:123-221,D:272-412] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon protease homolog, mitochondrial ; ELECTRON MICROSCOPY

e7oxoE2[E:123-221,E:272-412] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon protease homolog, mitochondrial ; ELECTRON MICROSCOPY

e7oxoF2[F:123-221,F:272-412] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lon protease homolog, mitochondrial ; ELECTRON MICROSCOPY

e8d7uB2[B:42-339] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Protein cereblon ; ligands: QFC,ZN ; ELECTRON MICROSCOPY

e8d7vB1[B:42-339] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Protein cereblon ; ligands: QFC,ZN ; ELECTRON MICROSCOPY

e8d7wB2[B:42-339] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Protein cereblon ; ligands: QFC,ZN ; ELECTRON MICROSCOPY

e8d7zB1[B:45-339] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Protein cereblon ; ligands: QFC,ZN ; ELECTRON MICROSCOPY

e8d80B1[B:45-339] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Protein cereblon ; ligands: ZN ; ELECTRON MICROSCOPY

e8d81B1[B:45-339] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Protein cereblon ; ligands: ZN ; ELECTRON MICROSCOPY

e8deyA1[A:71-339] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Protein cereblon ; ligands: ZN ; X-RAY DIFFRACTION 3.700Å

e8deyD2[D:71-339] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Protein cereblon ; ligands: ZN ; X-RAY DIFFRACTION 3.700Å

e7u8fA1[A:69-339] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Protein cereblon ; ligands: ZN ; X-RAY DIFFRACTION 3.150Å

e7u8fD2[D:69-339] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Protein cereblon ; ligands: ZN ; X-RAY DIFFRACTION 3.150Å

e8oizB2[B:44-339] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

; ligands: ZN ; X-RAY DIFFRACTION 2.500Å

e1zboA1[A:2-198] nonrep Image Pymol Jmol Links: PDB, SCOP, CATH

hypothetical protein BPP1347 ; X-RAY DIFFRACTION 2.6Å

contains a C-terminal alpha bundle subdomain

e3m65A1[A:4-209] nonrep Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

ATP-DEPENDENT PROTEASE LA 1 ; X-RAY DIFFRACTION 2.6Å

contains a C-terminal alpha bundle subdomain

e4ci1B1[B:47-320] nonrep Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

PROTEIN CEREBLON ; X-RAY DIFFRACTION 2.98Å

contains a C-terminal alpha-bundle subdomain

e4tz4C1[C:48-319] nonrep Image Pymol Jmol Links: PDB, SCOP, CATH

Protein cereblon ; X-RAY DIFFRACTION 3.010Å

contains a C-terminal alpha bundle subdomain

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.

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