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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

X: Phage tail fiber protein trimerization domain
H: Phage tail fiber protein trimerization domain
T: Phage tail fiber protein trimerization domain
F: BppL_N

PF18338 CL0606

Representatives:

Domain assembly:

e2f0cA2[A:17-62] nonrep Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

PHAGE TP901-1 ORF49 (BPP) , X-RAY DIFFRACTION 1.65Å

e3d8mA2[A:17-62] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Baseplate protein, Receptor binding protein ; X-RAY DIFFRACTION 3.35Å

e4diwA2[A:2-62] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB

e3u6xA2[A:2-62] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 2.6Å

e4hepA2[A:2-62] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 1.75Å

e4diwX2[X:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB

e4diwu2[u:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB

e3u6xB2[B:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 2.6Å

e4diwT2[T:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB

e4diws2[s:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB

e4diwD2[D:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB

e4diw12[1:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB

e3u6xL2[L:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 2.6Å

e3u6xD2[D:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 2.6Å

e3u6xI2[I:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 2.6Å

e4diwV2[V:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB

e4diwj2[j:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB

e4diwp2[p:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB

e4diwi2[i:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB

e4diwv2[v:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB

e4diwn2[n:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB

e4diwJ2[J:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB

e4diwO2[O:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB

e3u6xJ2[J:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 2.6Å

e3u6xG2[G:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 2.6Å

e4diwZ2[Z:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB

e3u6xQ2[Q:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 2.6Å

e4diwS2[S:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB

e4diwF2[F:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB

e4diwa2[a:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB

e4diwN2[N:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB

e3u6xM2[M:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 2.6Å

e4diwy2[y:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB

e4diwL2[L:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB

e4diwm2[m:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB

e4diwb2[b:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB

e4diwC2[C:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB

e3u6xP2[P:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 2.6Å

e4diwE2[E:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB

e3u6xN2[N:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 2.6Å

e3u6xC2[C:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 2.6Å

e4diwP2[P:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB

e4diwg2[g:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB

e4diwQ2[Q:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB

e3u6xK2[K:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 2.6Å

e4diwz2[z:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB

e4diwq2[q:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB

e4diwK2[K:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB

e3u6xO2[O:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 2.6Å

e3u6xH2[H:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 2.6Å

e4diwY2[Y:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB

e4diwr2[r:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB

e4diwH2[H:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB

e4diw22[2:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB

e4diwd2[d:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB

e3u6xE2[E:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 2.6Å

e4diwk2[k:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB

e4diww2[w:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB

e4diwh2[h:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB

e4diwU2[U:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB

e4diwW2[W:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB

e4diwo2[o:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB

e3u6xF2[F:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 2.6Å

e4diwR2[R:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB

e4diwM2[M:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB

e3u6xR2[R:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 2.6Å

e4diwe2[e:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB

e4diwl2[l:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB

e4diwG2[G:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB

e4diwB2[B:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB

e4diwx2[x:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB

e4diwc2[c:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB

e4diwt2[t:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB

e4diwI2[I:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB

e4diwf2[f:1-61] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB

e3hg0A2[A:33-62] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BASEPLATE PROTEIN ; X-RAY DIFFRACTION 2.1Å

e3hg0B2[B:34-62] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BASEPLATE PROTEIN ; X-RAY DIFFRACTION 2.1Å

e3da0C2[C:33-62] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Cleaved chimeric receptor binding protein from bacteriophages TP901-1 and p2 ; X-RAY DIFFRACTION 1.65Å

e4hemA2[A:34-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 1.65Å

e4hemB2[B:34-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 1.65Å

e4hemC1[C:33-62] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 1.65Å

e4v96BA2[BA:2-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 3.8Å

e4v96BB2[BB:2-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 3.8Å

e4v96BC2[BC:2-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 3.8Å

e4v96BD2[BD:2-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 3.8Å

e4v96BE2[BE:2-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 3.8Å

e4v96BF2[BF:2-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 3.8Å

e4v96BG2[BG:2-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 3.8Å

e4v96BH2[BH:2-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 3.8Å

e4v96BI2[BI:2-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 3.8Å

e4v96BJ2[BJ:2-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 3.8Å

e4v96BK2[BK:2-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 3.8Å

e4v96BL2[BL:2-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 3.8Å

e4v96BM2[BM:2-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 3.8Å

e4v96BN2[BN:2-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 3.8Å

e4v96BO2[BO:2-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 3.8Å

e4v96BP2[BP:2-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 3.8Å

e4v96BQ2[BQ:2-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 3.8Å

e4v96BR2[BR:2-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 3.8Å

e4v96BS2[BS:2-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 3.8Å

e4v96BT2[BT:2-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 3.8Å

e4v96BU2[BU:2-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 3.8Å

e4v96BV2[BV:2-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 3.8Å

e4v96BW2[BW:2-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 3.8Å

e4v96BX2[BX:2-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 3.8Å

e4v96BY2[BY:2-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 3.8Å

e4v96BZ2[BZ:2-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 3.8Å

e4v96Ba2[Ba:2-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 3.8Å

e4v96Bb2[Bb:2-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 3.8Å

e4v96Bc2[Bc:2-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 3.8Å

e4v96Bd1[Bd:2-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 3.8Å

e4v96Be2[Be:2-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 3.8Å

e4v96Bf2[Bf:2-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 3.8Å

e4v96Bg2[Bg:2-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 3.8Å

e4v96Bh2[Bh:2-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 3.8Å

e4v96Bi2[Bi:2-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 3.8Å

e4v96Bj2[Bj:2-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 3.8Å

e4v96Bk2[Bk:2-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 3.8Å

e4v96Bl2[Bl:2-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 3.8Å

e4v96Bm2[Bm:2-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 3.8Å

e4v96Bn2[Bn:2-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 3.8Å

e4v96Bo2[Bo:2-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 3.8Å

e4v96Bp2[Bp:2-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 3.8Å

e4v96Bq2[Bq:2-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 3.8Å

e4v96Br2[Br:2-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 3.8Å

e4v96Bs2[Bs:2-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 3.8Å

e4v96Bt2[Bt:2-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 3.8Å

e4v96Bu2[Bu:2-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 3.8Å

e4v96Bv2[Bv:2-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 3.8Å

e4v96Bw2[Bw:2-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 3.8Å

e4v96Bx2[Bx:2-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 3.8Å

e4v96By2[By:2-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 3.8Å

e4v96Bz2[Bz:2-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 3.8Å

e4v96B12[B1:2-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 3.8Å

e4v96B22[B2:2-61] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BPP ; X-RAY DIFFRACTION 3.8Å

Domain assembly:

e2f0cB2[B:17-62] nonrep Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

PHAGE TP901-1 ORF49 (BPP) , X-RAY DIFFRACTION 1.65Å

e2f0cC2[C:17-62] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

PHAGE TP901-1 ORF49 (BPP) , X-RAY DIFFRACTION 1.65Å

Domain assembly:

e2f0cC2[C:17-62] nonrep Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

PHAGE TP901-1 ORF49 (BPP) , X-RAY DIFFRACTION 1.65Å

e2f0cB2[B:17-62] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

PHAGE TP901-1 ORF49 (BPP) , X-RAY DIFFRACTION 1.65Å

e3ejcA2[A:2-62] * nonrep Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BASEPLATE PROTEIN (BPP) ; X-RAY DIFFRACTION 1.85Å

e3hg0C2[C:32-62] * nonrep Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

BASEPLATE PROTEIN ; X-RAY DIFFRACTION 2.1Å

Domain assembly:

e5e7tH1[H:1-57] nonrep Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Major structural protein 1 , X-RAY DIFFRACTION 2.9Å

e5e7tG1[G:2-57] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Major structural protein 1 , X-RAY DIFFRACTION 2.9Å

e5e7tI1[I:1-57] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI

Major structural protein 1 , X-RAY DIFFRACTION 2.9Å

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 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