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X - Possible homology level

H - Homology level

T - Topology level

F - Family level

* - Provisional representative

Keyword search

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

X: Immunoglobulin-like beta-sandwich
H: Immunoglobulin-related
T: Immunoglobulin/Fibronectin type III/E set domains/PapD-like
F: Ig_2

PF13895 CL0159

Representatives:

e1fnlA1[A:3-86] nonrep Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

LOW AFFINITY IMMUNOGLOBULIN GAMMA FC REGION RECEPTOR III-B ; ligands: HG ; X-RAY DIFFRACTION 1.8Å

e1fnlA2[A:87-175] nonrep Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

LOW AFFINITY IMMUNOGLOBULIN GAMMA FC REGION RECEPTOR III-B ; ligands: HG ; X-RAY DIFFRACTION 1.8Å

e1ugnA1[A:2-97] nonrep Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Leukocyte immunoglobulin-like receptor 1 ; X-RAY DIFFRACTION 1.8Å

e1xauA1[A:11-114] nonrep Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed,

B- AND T-LYMPHOCYTE ATTENUATOR ; ligands: CD ; X-RAY DIFFRACTION 1.8Å

e1uctA1[A:2-100] nonrep Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

IMMUNOGLOBULIN ALPHA FC RECEPTOR ; X-RAY DIFFRACTION 2.1Å

e2oz4A1[A:283-366] nonrep Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

INTERCELLULAR ADHESION MOLECULE 1 ; ligands: NAG ; X-RAY DIFFRACTION 2.7Å

e1iraY2[Y:102-204] nonrep Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

INTERLEUKIN-1 RECEPTOR ; ligands: NAG ; X-RAY DIFFRACTION 2.70Å

e6ewcH1[H:4-97] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Leukocyte immunoglobulin-like receptor subfamily B member 1 ; X-RAY DIFFRACTION 3.200Å

e6ewoD1[D:4-97] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

LIR-1 ; X-RAY DIFFRACTION 2.300Å

e6ewoH2[H:6-97] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

LIR-1 ; X-RAY DIFFRACTION 2.300Å

e6grqA4[A:220-314] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Paired immunoglobulin-like receptor B ; X-RAY DIFFRACTION 3.30Å

e6grqA1[A:25-120] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Paired immunoglobulin-like receptor B ; X-RAY DIFFRACTION 3.30Å

e6grsA4[A:223-317] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Paired immunoglobulin-like receptor B ; X-RAY DIFFRACTION 3.4Å

e6grsB4[B:220-315] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Paired immunoglobulin-like receptor B ; X-RAY DIFFRACTION 3.4Å

e6grsA1[A:29-222] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Paired immunoglobulin-like receptor B ; X-RAY DIFFRACTION 3.4Å

e6grsB1[B:26-120] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Paired immunoglobulin-like receptor B ; X-RAY DIFFRACTION 3.4Å

e6grtA1[A:25-120] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Paired immunoglobulin-like receptor B ; X-RAY DIFFRACTION 4.50Å

e6grtA4[A:220-315] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Paired immunoglobulin-like receptor B ; X-RAY DIFFRACTION 4.50Å

e6grtB1[B:25-222] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Paired immunoglobulin-like receptor B ; ligands: NAG ; X-RAY DIFFRACTION 4.50Å

e6k7oA1[A:2-95] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Leukocyte immunoglobulin-like receptor subfamily B member 4 ; X-RAY DIFFRACTION 3.00Å

e6k7oP1[P:2-95] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Leukocyte immunoglobulin-like receptor subfamily B member 4 ; X-RAY DIFFRACTION 3.00Å

e6k7oR1[R:2-95] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Leukocyte immunoglobulin-like receptor subfamily B member 4 ; X-RAY DIFFRACTION 3.00Å

e6k7oQ1[Q:2-95] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Leukocyte immunoglobulin-like receptor subfamily B member 4 ; X-RAY DIFFRACTION 3.00Å

e6aedA3[A:2-97] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Leukocyte immunoglobulin-like receptor subfamily B member 2 ; X-RAY DIFFRACTION 3.797Å

e6aeeG3[G:2-97] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Leukocyte immunoglobulin-like receptor subfamily B member 1 ; X-RAY DIFFRACTION 3.30Å

e6aeeH3[H:2-97] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Leukocyte immunoglobulin-like receptor subfamily B member 1 ; X-RAY DIFFRACTION 3.30Å

e6k60H1[H:9-97] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Leukocyte immunoglobulin-like receptor subfamily B member 1 ; X-RAY DIFFRACTION 3.149Å

e6k60D1[D:5-97] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Leukocyte immunoglobulin-like receptor subfamily B member 1 ; X-RAY DIFFRACTION 3.149Å

e6zdxB3[B:2-97] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Leukocyte immunoglobulin-like receptor subfamily B member 1 ; X-RAY DIFFRACTION 3.00Å

e7nmuBBB2[BBB:6-92] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Platelet glycoprotein VI ; X-RAY DIFFRACTION 2.498Å

e7nmuAAA1[AAA:9-92] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Platelet glycoprotein VI ; X-RAY DIFFRACTION 2.498Å

e7jz1H3[H:108-229] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

MGC34 heavy chain ; X-RAY DIFFRACTION 3.350Å

e7jz4A1[A:104-233] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

MGD21 heavy chain ; ligands: NAG,PO4 ; X-RAY DIFFRACTION 2.747Å

e7jziA1[A:108-205] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

LAIR1 ectodomain from antibody MGD21 ; X-RAY DIFFRACTION 2.700Å

e7jziC1[C:108-205] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

LAIR1 ectodomain from antibody MGD21 ; X-RAY DIFFRACTION 2.700Å

e7jzkC1[C:108-205] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

LAIR1 ecotodomain from MGD21 antibody ; X-RAY DIFFRACTION 2.450Å

e7jzkA1[A:108-212] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

LAIR1 ecotodomain from MGD21 antibody ; X-RAY DIFFRACTION 2.450Å

e7jz4C2[C:104-233] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

MGD21 heavy chain ; ligands: NAG,PO4 ; X-RAY DIFFRACTION 2.747Å

e7f9lG1[G:25-123] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Leukocyte-associated immunoglobulin-like receptor 1 ; X-RAY DIFFRACTION 2.70Å

e7f9lH1[H:25-123] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Leukocyte-associated immunoglobulin-like receptor 1 ; X-RAY DIFFRACTION 2.70Å

e7f9lI1[I:25-123] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Leukocyte-associated immunoglobulin-like receptor 1 ; X-RAY DIFFRACTION 2.70Å

e7f9lJ1[J:25-123] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Leukocyte-associated immunoglobulin-like receptor 1 ; X-RAY DIFFRACTION 2.70Å

e7f9lK1[K:25-121] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Leukocyte-associated immunoglobulin-like receptor 1 ; X-RAY DIFFRACTION 2.70Å

e7f9lL1[L:26-122] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Leukocyte-associated immunoglobulin-like receptor 1 ; X-RAY DIFFRACTION 2.70Å

e7f9mC1[C:25-123] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Leukocyte-associated immunoglobulin-like receptor 1 ; X-RAY DIFFRACTION 2.90Å

e7f9mD1[D:25-123] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Leukocyte-associated immunoglobulin-like receptor 1 ; X-RAY DIFFRACTION 2.90Å

e7f9nC1[C:25-122] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Leukocyte-associated immunoglobulin-like receptor 1 ; X-RAY DIFFRACTION 3.00Å

e7f9nD1[D:25-121] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Leukocyte-associated immunoglobulin-like receptor 1 ; X-RAY DIFFRACTION 3.00Å

e7r58A1[A:89-183] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Platelet glycoprotein VI ; ligands: GOL ; X-RAY DIFFRACTION 1.90Å

e7r58A2[A:3-88] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Platelet glycoprotein VI ; ligands: CL,GOL,SCN ; X-RAY DIFFRACTION 1.90Å

e8skuR2[R:6-99] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

; ELECTRON MICROSCOPY

e8grxB2[B:25-220] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

; ELECTRON MICROSCOPY

e3wjjC4[C:5-83] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Low affinity immunoglobulin gamma Fc region receptor II-b ; X-RAY DIFFRACTION 2.60Å

e4x4mE3[E:21-102] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

High affinity immunoglobulin gamma Fc receptor I ; X-RAY DIFFRACTION 3.485Å

e2e5eA1[A:21-121] Image Pymol Jmol Links: PDB, SCOP, CATH

Advanced glycosylation end product-specific receptor ; SOLUTION NMR

e4lp4A3[A:20-118] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Advanced glycosylation end product-specific receptor ; ligands: NA ; X-RAY DIFFRACTION 2.400Å

e4lp4B3[B:20-118] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Advanced glycosylation end product-specific receptor ; ligands: NA ; X-RAY DIFFRACTION 2.400Å

e4lp5A8[A:20-118] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Advanced glycosylation end product-specific receptor ; X-RAY DIFFRACTION 3.800Å

e3s59B5[B:22-118] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB

e3s58B5[B:21-118] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB

e4oi7B2[B:21-118] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

ADVANCED GLYCOSYLATION END PRODUCT-SPECIFIC RECEPTOR ; ligands: EDO ; X-RAY DIFFRACTION 3.1Å

e4oi8B2[B:21-118] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

ADVANCED GLYCOSYLATION END PRODUCT-SPECIFIC RECEPTOR ; X-RAY DIFFRACTION 3.1Å

e4of5B2[B:22-118] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Advanced glycosylation end product-specific receptor ; X-RAY DIFFRACTION

e4ofvB2[B:21-118] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Advanced glycosylation end product-specific receptor ; X-RAY DIFFRACTION 3.100Å

e2l7uA1[A:1-105] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Advanced glycosylation end product-specific receptor ; SOLUTION NMR

e2movA1[A:1-105] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

ADVANCED GLYCOSYLATION END PRODUCT-SPECIFIC RECEPTOR ; ligands: IOR ; SOLUTION NMR

e3cjjA2[A:22-118] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

ADVANCED GLYCOSYLATION END PRODUCT-SPECIFIC RECEPTOR ; ligands: ZN ; X-RAY DIFFRACTION 1.85Å

e2mjwA1[A:21-121] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Advanced glycosylation end product-specific receptor ; SOLUTION NMR

e2mjwC1[C:21-121] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Advanced glycosylation end product-specific receptor ; SOLUTION NMR

e4p2yA3[A:21-118] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Advanced glycosylation end product-specific receptor ; ligands: ACT ; X-RAY DIFFRACTION 2.300Å

e2m1kA1[A:21-121] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Advanced glycosylation end product-specific receptor ; SOLUTION NMR

e2m1kC1[C:21-121] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Advanced glycosylation end product-specific receptor ; SOLUTION NMR

e4im8A1[A:22-117] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

ADVANCED GLYCATION END-PRODUCTS RECEPTOR ; X-RAY DIFFRACTION 3.5Å

e3o3uN3[N:371-1119] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Maltose-binding periplasmic protein, Advanced glycosylation end product-specific receptor ; ligands: SO4 ; X-RAY DIFFRACTION 1.49Å

e3s58A2[A:23-118] Image Pymol Jmol Links: PDB, SCOP, CATH

e4of5A1[A:23-121] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Advanced glycosylation end product-specific receptor ; X-RAY DIFFRACTION

e4ofvA1[A:23-121] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Advanced glycosylation end product-specific receptor ; X-RAY DIFFRACTION 3.100Å

e4oi7A1[A:23-121] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

ADVANCED GLYCOSYLATION END PRODUCT-SPECIFIC RECEPTOR ; ligands: EDO ; X-RAY DIFFRACTION 3.1Å

e4oi8A1[A:23-121] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

ADVANCED GLYCOSYLATION END PRODUCT-SPECIFIC RECEPTOR ; X-RAY DIFFRACTION 3.1Å

e4ybhA1[A:21-118] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Advanced glycosylation end product-specific receptor ; ligands: ACT ; X-RAY DIFFRACTION 2.400Å

e6xq1A1[A:20-118] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Advanced glycosylation end product-specific receptor ; ligands: ACT,CL,V74 ; X-RAY DIFFRACTION 1.51Å

e7lmwA1[A:20-118] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Advanced glycosylation end product-specific receptor ; ligands: ACT,Y6P ; X-RAY DIFFRACTION 2.50Å

e7lmwB1[B:20-118] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Advanced glycosylation end product-specific receptor ; ligands: ACT,Y6P ; X-RAY DIFFRACTION 2.50Å

e6xq1B1[B:20-118] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Advanced glycosylation end product-specific receptor ; ligands: ACT,CL,V74 ; X-RAY DIFFRACTION 1.51Å

e6xq3A1[A:20-118] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Advanced glycosylation end product-specific receptor ; ligands: ACT,CL,V6Y ; X-RAY DIFFRACTION 1.70Å

e6xq3B1[B:20-118] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Advanced glycosylation end product-specific receptor ; ligands: ACT,CL,V6Y ; X-RAY DIFFRACTION 1.70Å

e6xq5A1[A:20-118] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Advanced glycosylation end product-specific receptor ; ligands: ACT,CL,V6M ; X-RAY DIFFRACTION 1.80Å

e6xq5B1[B:20-118] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Advanced glycosylation end product-specific receptor ; ligands: ACT,CL,V6M ; X-RAY DIFFRACTION 1.80Å

e6xq6A1[A:20-118] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Advanced glycosylation end product-specific receptor ; ligands: ACT,CL,V6P ; X-RAY DIFFRACTION 1.90Å

e6xq6B1[B:20-118] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Advanced glycosylation end product-specific receptor ; ligands: ACT,CL,V6P ; X-RAY DIFFRACTION 1.90Å

e6xq7A1[A:20-118] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Advanced glycosylation end product-specific receptor ; ligands: ACT,V6V ; X-RAY DIFFRACTION 1.80Å

e6xq7B1[B:20-118] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Advanced glycosylation end product-specific receptor ; ligands: ACT,CL,V6V ; X-RAY DIFFRACTION 1.80Å

e6xq8A1[A:20-118] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Advanced glycosylation end product-specific receptor ; ligands: ACT,V6M,V6P ; X-RAY DIFFRACTION 1.82Å

e6xq8B1[B:20-118] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Advanced glycosylation end product-specific receptor ; ligands: ACT,CL,V6M,V6P ; X-RAY DIFFRACTION 1.82Å

e6xq9A1[A:20-118] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Advanced glycosylation end product-specific receptor ; ligands: ACT,V6M,V6S ; X-RAY DIFFRACTION 2.30Å

e6xq9B1[B:20-118] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Advanced glycosylation end product-specific receptor ; ligands: ACT,V6M,V6S ; X-RAY DIFFRACTION 2.30Å

e7lmlA1[A:20-118] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Advanced glycosylation end product-specific receptor ; ligands: ACT,CL,Y6S ; X-RAY DIFFRACTION 2.14983Å

e7lmlB1[B:20-118] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Advanced glycosylation end product-specific receptor ; ligands: ACT,CL,Y6S ; X-RAY DIFFRACTION 2.14983Å

e6yaxAAA2[AAA:131-219] Image Pymol Jmol Links: PDB, SCOP, CATH

Low affinity immunoglobulin gamma Fc region receptor II-c ; ligands: NAG,PG4 ; X-RAY DIFFRACTION 2.80Å

e7tzgC1[C:172-261] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Lymphocyte activation gene 3 protein ; ligands: NAG ; X-RAY DIFFRACTION 3.710Å

Previous

e1e07A3[A:203-286] nonrep Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

CARCINOEMBRYONIC ANTIGEN ; SOLUTION SCATTERING

e1e07A5[A:381-464] nonrep Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

CARCINOEMBRYONIC ANTIGEN ; SOLUTION SCATTERING

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.

X: Glycosyl hydrolase domain-like

some similarity with Ig fold

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