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

looks like an elaborated ferredoxin



Representatives:
e1j98A1[A:4-157]
nonrep
Image
Pymol
Jmol Links:
PDB,
SCOP,
CATH, PubMed,
DOI
AUTOINDUCER-2 PRODUCTION PROTEIN LUXS ; ligands: ZN ; X-RAY DIFFRACTION 1.20Å
e2fqtA1[A:4-157] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
S-RIBOSYLHOMOCYSTEINE LYASE ; ligands: CO,H1D,SO4 ; X-RAY DIFFRACTION 1.79Å
e1jqwA1[A:8-157] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Autoinducer-2 production protein luxS ; ligands: HCS,ZN ; X-RAY DIFFRACTION 2.3Å
e1j6xA1[A:5-151] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
AUTOINDUCER-2 PRODUCTION PROTEIN LUXS ; ligands: MET,ZN ; X-RAY DIFFRACTION 2.38Å
e2fqoA1[A:4-157] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
S-RIBOSYLHOMOCYSTEINE LYASE ; ligands: CO,HYI,SO4 ; X-RAY DIFFRACTION 1.87Å
e1jviA1[A:4-157] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Autoinducer-2 production protein luxS ; ligands: HCS,RHC,SO4,ZN ; X-RAY DIFFRACTION 2.2Å
e1ie0A1[A:4-157] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
AUTOINDUCER-2 PRODUCTION PROTEIN LUXS ; ligands: GOL,ZN ; X-RAY DIFFRACTION 1.6Å
e1j6xB1[B:5-151] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
AUTOINDUCER-2 PRODUCTION PROTEIN LUXS ; ligands: MET,ZN ; X-RAY DIFFRACTION 2.38Å
e1vgxA1[A:8-156] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
S-ribosylhomocysteinase ; ligands: ZN ; X-RAY DIFFRACTION 1.90Å
e1vjeB1[B:7-156] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Autoinducer-2 production protein LuxS ; ligands: MSE,ZN ; X-RAY DIFFRACTION 1.64Å
e1vjeA1[A:8-156] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Autoinducer-2 production protein LuxS ; ligands: MSE,ZN ; X-RAY DIFFRACTION 1.64Å
e1innB1[B:7-156] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
AUTOINDUCER-2 PRODUCTION PROTEIN LUXS ; ligands: MET,ZN ; X-RAY DIFFRACTION 1.80Å
e1vgxB1[B:6-156] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
S-ribosylhomocysteinase ; ligands: ZN ; X-RAY DIFFRACTION 1.90Å
e1vh2A1[A:7-158] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
S-RIBOSYLHOMOCYSTEINASE ; ligands: ZN ; X-RAY DIFFRACTION 2.0Å
e1joeB1[B:9-156] Image Pymol Jmol Links: PDB, SCOP, CATH
AUTOINDUCER-2 PRODUCTION PROTEIN ; ligands: HG,ZN ; X-RAY DIFFRACTION 2.30Å
e1joeA1[A:9-156] Image Pymol Jmol Links: PDB, SCOP, CATH
AUTOINDUCER-2 PRODUCTION PROTEIN ; ligands: HG,ZN ; X-RAY DIFFRACTION 2.30Å
e1joeC1[C:9-156] Image Pymol Jmol Links: PDB, SCOP, CATH
AUTOINDUCER-2 PRODUCTION PROTEIN ; ligands: HG,ZN ; X-RAY DIFFRACTION 2.30Å
e1joeD1[D:9-156] Image Pymol Jmol Links: PDB, SCOP, CATH
AUTOINDUCER-2 PRODUCTION PROTEIN ; ligands: HG,ZN ; X-RAY DIFFRACTION 2.30Å
e1j6vA1[A:7-157] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
AUTOINDUCER-2 PRODUCTION PROTEIN LUXS ; ligands: ZN ; X-RAY DIFFRACTION 2.10Å
e1innA1[A:6-156] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
AUTOINDUCER-2 PRODUCTION PROTEIN LUXS ; ligands: MET,ZN ; X-RAY DIFFRACTION 1.80Å
e1j6wB1[B:3-162] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
AUTOINDUCER-2 PRODUCTION PROTEIN LUXS ; ligands: MET,ZN ; X-RAY DIFFRACTION 2.10Å
e1yclA1[A:4-157] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
S-ribosylhomocysteinase ; ligands: CO,KRI,SO4 ; X-RAY DIFFRACTION 1.8Å
e4xchA1[A:12-160] Image Pymol Jmol Links: PDB, SCOP, CATH
S-ribosylhomocysteine lyase ; ligands: ZN ; X-RAY DIFFRACTION 1.9Å
e4xchB1[B:12-160] Image Pymol Jmol Links: PDB, SCOP, CATH
S-ribosylhomocysteine lyase ; ligands: ZN ; X-RAY DIFFRACTION 1.9Å
e4xchC1[C:12-160] Image Pymol Jmol Links: PDB, SCOP, CATH
S-ribosylhomocysteine lyase ; ligands: ZN ; X-RAY DIFFRACTION 1.9Å
e4xchD1[D:12-160] Image Pymol Jmol Links: PDB, SCOP, CATH
S-ribosylhomocysteine lyase ; ligands: ZN ; X-RAY DIFFRACTION 1.9Å
e5e68B1[B:3-174] Image Pymol Jmol Links: PDB, SCOP, CATH
S-ribosylhomocysteine lyase ; ligands: MET,PAV,ZN ; X-RAY DIFFRACTION 1.58Å
e5v2wA1[A:3-169] Image Pymol Jmol Links: PDB, SCOP, CATH
S-ribosylhomocysteine lyase ; ligands: ZN ; X-RAY DIFFRACTION 2.30Å
e5v2wB1[B:3-174] Image Pymol Jmol Links: PDB, SCOP, CATH
S-ribosylhomocysteine lyase ; ligands: ZN ; X-RAY DIFFRACTION 2.30Å

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