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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

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

X: HPr-like
H: HPr-like
T: HPr-like
F: PTS-HPr

PF00381

Representatives:

e1cm3A1[A:1-85] nonrep Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

HISTIDINE-CONTAINING PROTEIN ; X-RAY DIFFRACTION 1.6Å

e1pchA1[A:2-89] nonrep Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

PHOSPHOCARRIER PROTEIN ; ligands: SO4 ; X-RAY DIFFRACTION 1.80Å

e1ptfA1[A:1-87] nonrep Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

HISTIDINE-CONTAINING PHOSPHOCARRIER PROTEIN HPR ; X-RAY DIFFRACTION

e1mo1D1[D:1-87] Image Pymol Jmol Links: PDB, SCOP, CATH

Hpr-like protein crh ; ligands: GOL,SO4 ; X-RAY DIFFRACTION 1.80Å

e1qr5A1[A:1-87] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed,

PHOSPHOCARRIER PROTEIN HPR ; SOLUTION NMR

e1qfrA1[A:1-87] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

PHOSPHOCARRIER PROTEIN HPR ; SOLUTION NMR

e1fu0A1[A:1-87] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

PHOSPHOCARRIER PROTEIN HPR ; X-RAY DIFFRACTION 1.90Å

e1ka5A1[A:1-87] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

PHOSPHOCARRIER PROTEIN HPR ; SOLUTION NMR

e2ak7B1[B:1-86] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

HPR-LIKE PROTEIN CRH ; ligands: SO4 ; X-RAY DIFFRACTION 2.0Å

e1kkmH1[H:2-87] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

PHOSPHOCARRIER PROTEIN HPR ; ligands: CA,PO4 ; X-RAY DIFFRACTION 2.80Å

e1sphB1[B:2-87] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

HISTIDINE-CONTAINING PHOSPHOCARRIER PROTEIN HPR ; X-RAY DIFFRACTION

e2oenL1[L:2-87] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

PHOSPHOCARRIER PROTEIN HPR ; X-RAY DIFFRACTION 3.17Å

e2nzuL1[L:2-87] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

PHOSPHOCARRIER PROTEIN HPR ; ligands: SO4 ; X-RAY DIFFRACTION 2.5Å

e1mo1C1[C:1-87] Image Pymol Jmol Links: PDB, SCOP, CATH

Hpr-like protein crh ; ligands: GOL,SO4 ; X-RAY DIFFRACTION 1.80Å

e1mu4A1[A:1-86] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

HPr-like protein crh ; ligands: SO4 ; X-RAY DIFFRACTION 1.8Å

e1rzrY1[Y:2-87] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

PHOSPHOCARRIER PROTEIN HPR ; X-RAY DIFFRACTION 2.8Å

e1fu0B1[B:101-187] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

PHOSPHOCARRIER PROTEIN HPR ; X-RAY DIFFRACTION 1.90Å

e1mu4B1[B:1-87] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

HPr-like protein crh ; ligands: SO4 ; X-RAY DIFFRACTION 1.8Å

e2hprA1[A:2-87] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

HISTIDINE-CONTAINING PHOSPHOCARRIER PROTEIN HPR ; ligands: SO4 ; X-RAY DIFFRACTION 2.0Å

e1kklH1[H:3-87] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

PHOSPHOCARRIER PROTEIN HPR ; X-RAY DIFFRACTION 2.80Å

e1rzrT1[T:2-87] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

PHOSPHOCARRIER PROTEIN HPR ; X-RAY DIFFRACTION 2.8Å

e2hidA1[A:2-87] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed,

HISTIDINE CONTAINING PROTEIN ; SOLUTION NMR

e1rzrL1[L:2-87] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

PHOSPHOCARRIER PROTEIN HPR ; X-RAY DIFFRACTION 2.8Å

e1kklJ1[J:1-87] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

PHOSPHOCARRIER PROTEIN HPR ; X-RAY DIFFRACTION 2.80Å

e1sphA1[A:2-87] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

HISTIDINE-CONTAINING PHOSPHOCARRIER PROTEIN HPR ; X-RAY DIFFRACTION

e1rzrS1[S:2-87] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

PHOSPHOCARRIER PROTEIN HPR ; X-RAY DIFFRACTION 2.8Å

e1jemA1[A:2-87] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed,

HISTIDINE CONTAINING PROTEIN ; SOLUTION NMR

e1mo1A1[A:1-87] Image Pymol Jmol Links: PDB, SCOP, CATH

Hpr-like protein crh ; ligands: GOL,SO4 ; X-RAY DIFFRACTION 1.80Å

e1kkmJ1[J:2-87] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

PHOSPHOCARRIER PROTEIN HPR ; ligands: CA,PO4 ; X-RAY DIFFRACTION 2.80Å

e2nzvL1[L:2-87] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

PHOSPHOCARRIER PROTEIN HPR ; ligands: SO4 ; X-RAY DIFFRACTION 3.0Å

e1kkmI1[I:2-87] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

PHOSPHOCARRIER PROTEIN HPR ; ligands: CA,PO4 ; X-RAY DIFFRACTION 2.80Å

e1kklI1[I:2-87] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

PHOSPHOCARRIER PROTEIN HPR ; X-RAY DIFFRACTION 2.80Å

e2ak7A1[A:1-86] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

HPR-LIKE PROTEIN CRH ; ligands: SO4 ; X-RAY DIFFRACTION 2.0Å

e1mo1B1[B:1-87] Image Pymol Jmol Links: PDB, SCOP, CATH

Hpr-like protein crh ; ligands: GOL,SO4 ; X-RAY DIFFRACTION 1.80Å

e1ggrB1[B:301-385] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

PHOSPHOCARRIER PROTEIN HPR ; SOLUTION NMR

e1j6tB1[B:301-385] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Phosphocarrier protein HPr ; SOLUTION NMR

e1vrcC1[C:201-285] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Phosphocarrier protein HPr ; SOLUTION NMR

e1opdA1[A:1-85] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

HISTIDINE-CONTAINING PROTEIN ; ligands: SO4 ; X-RAY DIFFRACTION

e1vrcD1[D:201-285] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Phosphocarrier protein HPr ; SOLUTION NMR

e3ezeB1[B:301-385] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

PROTEIN (PHOSPHOTRANSFERASE SYSTEM, HPR) ; ligands: PO3 ; SOLUTION NMR

e1cm2A1[A:1-85] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

HISTIDINE-CONTAINING PROTEIN ; X-RAY DIFFRACTION 1.8Å

e1pfhA1[A:1-85] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

PHOSPHO-HPR ; SOLUTION NMR

e2jelP1[P:1-85] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

HISTIDINE-CONTAINING PROTEIN ; ligands: SO4 ; X-RAY DIFFRACTION 2.5Å

e2rlzB1[B:1-85] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

HPr-like protein crh ; SOLID-STATE NMR

e1zvvP1[P:1-84] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

HPr-like protein crh ; ligands: IOD ; X-RAY DIFFRACTION 2.98Å

e1hdnA1[A:1-85] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

HISTIDINE-CONTAINING PHOSPHOCARRIER PROTEIN HPR ; SOLUTION NMR

e2rlzA1[A:1-85] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

HPr-like protein crh ; SOLID-STATE NMR

e1zvvJ1[J:1-84] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

HPr-like protein crh ; X-RAY DIFFRACTION 2.98Å

e3ezaB1[B:1-85] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

HISTIDINE-CONTAINING PHOSPHOCARRIER PROTEIN HPR ; SOLUTION NMR

e1zvvW1[W:1-84] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

HPr-like protein crh ; X-RAY DIFFRACTION 2.98Å

e1pohA1[A:1-85] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed,

HISTIDINE-CONTAINING PHOSPHOCARRIER PROTEIN HPR ; ligands: SO4 ; X-RAY DIFFRACTION

e3ezbB1[B:301-385] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

PROTEIN (PHOSPHOCARRIER PROTEIN HPR) ; SOLUTION NMR

e1k1cA1[A:2-85] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

catabolite repression HPr-like protein ; SOLUTION NMR

e3oqmS1[S:2-88] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

PHOSPHOCARRIER PROTEIN HPR ; X-RAY DIFFRACTION 2.96Å

e3oqoS1[S:2-88] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

PHOSPHOCARRIER PROTEIN HPR ; ligands: SO4 ; X-RAY DIFFRACTION 2.97Å

e3le5A1[A:1-87] Image Pymol Jmol Links: PDB, SCOP, CATH

PHOSPHOTRANSFERASE SYSTEM, HPR-RELATED PROTEINS ; X-RAY DIFFRACTION 2.0Å

e2xdfC1[C:601-685] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

PHOSPHOCARRIER PROTEIN HPR ; SOLUTION SCATTERING

e3ihsA1[A:-2-82] Image Pymol Jmol Links: PDB, SCOP, CATH

PHOSPHOCARRIER PROTEIN HPR ; X-RAY DIFFRACTION 1.15Å

e2lrkD1[D:301-385] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

PHOSPHOCARRIER PROTEIN HPR ; SOLUTION NMR

e1txeA1[A:1-88] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Phosphocarrier protein HPr ; SOLUTION NMR

e2fepS1[S:2-88] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

PHOSPHOCARRIER PROTEIN HPR ; ligands: SO4 ; X-RAY DIFFRACTION 2.45Å

e1y4yA1[A:2-88] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Phosphocarrier protein HPr ; ligands: SO4 ; X-RAY DIFFRACTION 2.0Å

e1y4yB1[B:2-88] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Phosphocarrier protein HPr ; ligands: SO4 ; X-RAY DIFFRACTION 2.0Å

e1y4yC1[C:2-88] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Phosphocarrier protein HPr ; ligands: SO4 ; X-RAY DIFFRACTION 2.0Å

e1y50A1[A:2-88] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Phosphocarrier protein HPr ; ligands: SO4 ; X-RAY DIFFRACTION 2.0Å

e1y51A1[A:2-88] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Phosphocarrier protein HPr ; ligands: SO4 ; X-RAY DIFFRACTION 1.64Å

e1y51B1[B:2-88] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Phosphocarrier protein HPr ; ligands: SO4 ; X-RAY DIFFRACTION 1.64Å

e1y51C1[C:2-88] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Phosphocarrier protein HPr ; ligands: SO4 ; X-RAY DIFFRACTION 1.64Å

e3ccdA1[A:1-85] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Phosphocarrier protein HPr ; ligands: SO4 ; X-RAY DIFFRACTION 1.00Å

e3ccdB1[B:1-85] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Phosphocarrier protein HPr ; ligands: SO4 ; X-RAY DIFFRACTION 1.00Å

e2xdfD1[D:601-685] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

PHOSPHOCARRIER PROTEIN HPR ; SOLUTION SCATTERING

e3ihsB1[B:-1-82] Image Pymol Jmol Links: PDB, SCOP, CATH

PHOSPHOCARRIER PROTEIN HPR ; X-RAY DIFFRACTION 1.15Å

e3le1A1[A:1-87] Image Pymol Jmol Links: PDB, SCOP, CATH

Phosphotransferase system, HPr-related proteins ; ligands: CD ; X-RAY DIFFRACTION 1.51Å

e3le1B1[B:1-85] Image Pymol Jmol Links: PDB, SCOP, CATH

Phosphotransferase system, HPr-related proteins ; ligands: CD ; X-RAY DIFFRACTION 1.51Å

e3le3A1[A:1-88] Image Pymol Jmol Links: PDB, SCOP, CATH

Phosphotransferase system, HPr-related proteins ; X-RAY DIFFRACTION 1.86Å

e3le3B1[B:1-88] Image Pymol Jmol Links: PDB, SCOP, CATH

Phosphotransferase system, HPr-related proteins ; X-RAY DIFFRACTION 1.86Å

e3le3C1[C:1-87] Image Pymol Jmol Links: PDB, SCOP, CATH

Phosphotransferase system, HPr-related proteins ; X-RAY DIFFRACTION 1.86Å

e3le5B1[B:1-87] Image Pymol Jmol Links: PDB, SCOP, CATH

PHOSPHOTRANSFERASE SYSTEM, HPR-RELATED PROTEINS ; X-RAY DIFFRACTION 2.0Å

e3lfgA1[A:1-88] Image Pymol Jmol Links: PDB, SCOP, CATH

Phosphotransferase system, HPr-related proteins ; X-RAY DIFFRACTION 1.58Å

e3lfgB1[B:1-89] Image Pymol Jmol Links: PDB, SCOP, CATH

Phosphotransferase system, HPr-related proteins ; X-RAY DIFFRACTION 1.58Å

e3lfgC1[C:1-88] Image Pymol Jmol Links: PDB, SCOP, CATH

Phosphotransferase system, HPr-related proteins ; X-RAY DIFFRACTION 1.58Å

e3lnwA1[A:1-86] Image Pymol Jmol Links: PDB, SCOP, CATH

Phosphotransferase system, HPr-related proteins ; X-RAY DIFFRACTION 2.30Å

e3lnwB1[B:1-86] Image Pymol Jmol Links: PDB, SCOP, CATH

Phosphotransferase system, HPr-related proteins ; X-RAY DIFFRACTION 2.30Å

e3lnwC1[C:1-86] Image Pymol Jmol Links: PDB, SCOP, CATH

Phosphotransferase system, HPr-related proteins ; X-RAY DIFFRACTION 2.30Å

e3oqmD1[D:2-88] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

PHOSPHOCARRIER PROTEIN HPR ; X-RAY DIFFRACTION 2.96Å

e3oqnS1[S:2-88] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

PHOSPHOCARRIER PROTEIN HPR ; X-RAY DIFFRACTION 3.3Å

e3oqnD1[D:2-88] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

PHOSPHOCARRIER PROTEIN HPR ; X-RAY DIFFRACTION 3.3Å

e3oqoD1[D:2-88] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

PHOSPHOCARRIER PROTEIN HPR ; ligands: SO4 ; X-RAY DIFFRACTION 2.97Å

e2lrlD1[D:301-385] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

PHOSPHOCARRIER PROTEIN HPR ; ligands: PO3 ; SOLUTION NMR

e4xwjB1[B:1-83] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Phosphocarrier protein HPr ; X-RAY DIFFRACTION 2.0Å

e5t17A1[A:1-85] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Phosphocarrier protein NPr ; SOLUTION NMR

e5t1nA1[A:1-85] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Phosphocarrier protein NPr ; SOLUTION NMR

e5t1oA1[A:1-85] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Phosphocarrier protein NPr ; SOLUTION SCATTERING

e5ya0C1[C:1-85] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Phosphocarrier protein HPr ; ligands: HEZ,PO4 ; X-RAY DIFFRACTION 2.7Å

e5ya0D1[D:1-85] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Phosphocarrier protein HPr ; ligands: HEZ,PO4 ; X-RAY DIFFRACTION 2.7Å

e5ya1C1[C:1-85] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Phosphocarrier protein HPr ; ligands: HEZ,PO4 ; X-RAY DIFFRACTION 2.7Å

e5ya1D1[D:1-85] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Phosphocarrier protein HPr ; ligands: HEZ,PO4 ; X-RAY DIFFRACTION 2.7Å

e5ya2C1[C:1-85] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Phosphocarrier protein HPr ; ligands: HEZ,PO4 ; X-RAY DIFFRACTION 2.701Å

e5ya2D1[D:1-85] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Phosphocarrier protein HPr ; ligands: HEZ,PO4 ; X-RAY DIFFRACTION 2.701Å

e6kcrB1[B:1-85] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Phosphocarrier protein HPr ; X-RAY DIFFRACTION 3.5Å

e6kcrD1[D:1-85] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Phosphocarrier protein HPr ; X-RAY DIFFRACTION 3.5Å

e7ff5A1[A:1-84] Image Pymol Jmol Links: PDB, SCOP, CATH

Phosphocarrier, HPr family ; ligands: SO4 ; X-RAY DIFFRACTION 2.37Å

e7ff5B1[B:1-84] Image Pymol Jmol Links: PDB, SCOP, CATH

Phosphocarrier, HPr family ; ligands: SO4 ; X-RAY DIFFRACTION 2.37Å

e7ff5C1[C:1-84] Image Pymol Jmol Links: PDB, SCOP, CATH

Phosphocarrier, HPr family ; ligands: SO4 ; X-RAY DIFFRACTION 2.37Å

e7x7hB1[B:0-84] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

HPr family phosphocarrier protein ; X-RAY DIFFRACTION 2.00Å

e7x7hD1[D:0-84] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

HPr family phosphocarrier protein ; X-RAY DIFFRACTION 2.00Å

X: LuxS, MPP, ThrRS/AlaRS common domain

looks like an elaborated ferredoxin

X: ClpS-like

contains a HTH motif

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