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
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




Representatives:
e1x9pA2[A:134-298,A:373-433]
nonrep
Image
Pymol
Jmol Links:
PDB,
SCOP,
CATH, PubMed,
DOI
Penton protein ; ligands: C15 ; X-RAY DIFFRACTION 3.3Å
e1vszN1[N:134-298,N:373-433] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB
e2c9gA1[A:134-298,A:373-433] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
PENTON PROTEIN ; ELECTRON MICROSCOPY
e2c9gB1[B:134-298,B:373-433] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
PENTON PROTEIN ; ELECTRON MICROSCOPY
e2c9gC1[C:134-298,C:373-433] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
PENTON PROTEIN ; ELECTRON MICROSCOPY
e2c9gD1[D:134-298,D:373-433] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
PENTON PROTEIN ; ELECTRON MICROSCOPY
e2c9gE1[E:134-298,E:373-433] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
PENTON PROTEIN ; ELECTRON MICROSCOPY
e1x9tA1[A:134-296,A:375-433] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ligands: C15 ; X-RAY DIFFRACTION 3.5Å
e2bldA1[A:134-296,A:375-433] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB
e2bldB1[B:134-296,B:375-433] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB
e2bldC1[C:134-296,C:375-433] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB
e2bldD1[D:134-296,D:375-433] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB
e2bldE1[E:134-296,E:375-433] Image Pymol Jmol Links: PDB, SCOP, CATH Obsolete PDB
e2c6sA1[A:134-296,A:312-370] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
ADENOVIRUS 2,12 PENTON BASE CHIMERA ; X-RAY DIFFRACTION 3.600Å
e2c6sB1[B:134-296,B:312-370] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
ADENOVIRUS 2,12 PENTON BASE CHIMERA ; X-RAY DIFFRACTION 3.600Å
e2c6sC1[C:134-296,C:312-370] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
ADENOVIRUS 2,12 PENTON BASE CHIMERA ; X-RAY DIFFRACTION 3.600Å
e2c6sD1[D:134-296,D:312-370] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
ADENOVIRUS 2,12 PENTON BASE CHIMERA ; X-RAY DIFFRACTION 3.600Å
e2c6sE1[E:134-296,E:312-370] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
ADENOVIRUS 2,12 PENTON BASE CHIMERA ; X-RAY DIFFRACTION 3.600Å
e2c6sF1[F:134-296,F:312-370] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
ADENOVIRUS 2,12 PENTON BASE CHIMERA ; X-RAY DIFFRACTION 3.600Å
e2c6sG1[G:134-296,G:312-370] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
ADENOVIRUS 2,12 PENTON BASE CHIMERA ; X-RAY DIFFRACTION 3.600Å
e2c6sH1[H:134-296,H:312-370] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
ADENOVIRUS 2,12 PENTON BASE CHIMERA ; X-RAY DIFFRACTION 3.600Å
e2c6sI1[I:134-296,I:312-370] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
ADENOVIRUS 2,12 PENTON BASE CHIMERA ; X-RAY DIFFRACTION 3.600Å
e2c6sJ1[J:134-296,J:312-370] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
ADENOVIRUS 2,12 PENTON BASE CHIMERA ; X-RAY DIFFRACTION 3.600Å
e2c6sK1[K:134-296,K:312-370] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
ADENOVIRUS 2,12 PENTON BASE CHIMERA ; X-RAY DIFFRACTION 3.600Å
e2c6sL1[L:134-296,L:312-370] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
ADENOVIRUS 2,12 PENTON BASE CHIMERA ; X-RAY DIFFRACTION 3.600Å
e2c6sM1[M:134-296,M:312-370] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
ADENOVIRUS 2,12 PENTON BASE CHIMERA ; X-RAY DIFFRACTION 3.600Å
e2c6sN1[N:134-296,N:312-370] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
ADENOVIRUS 2,12 PENTON BASE CHIMERA ; X-RAY DIFFRACTION 3.600Å
e2c6sO1[O:134-296,O:312-370] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
ADENOVIRUS 2,12 PENTON BASE CHIMERA ; X-RAY DIFFRACTION 3.600Å
e2c9fA1[A:134-296,A:373-431] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
PENTON PROTEIN ; ELECTRON MICROSCOPY
e2c9fB1[B:134-296,B:373-431] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
PENTON PROTEIN ; ELECTRON MICROSCOPY
e2c9fC1[C:134-296,C:373-431] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
PENTON PROTEIN ; ELECTRON MICROSCOPY
e2c9fD1[D:134-296,D:373-431] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
PENTON PROTEIN ; ELECTRON MICROSCOPY
e2c9fE1[E:134-296,E:373-431] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
PENTON PROTEIN ; ELECTRON MICROSCOPY
e3iynM1[M:134-296,M:375-433] Image Pymol Jmol Links: PDB, SCOP, CATH
e3izoA1[A:134-296,A:375-433] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e3izoB1[B:134-296,B:375-433] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e3izoC1[C:134-296,C:375-433] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e3izoD1[D:134-296,D:375-433] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e3izoE1[E:134-296,E:375-433] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e3zifM2[M:128-344] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
PENTON PROTEIN ; ELECTRON MICROSCOPY
e4ar2A3[A:134-413] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
L2 PROTEIN III (PENTON BASE) ; X-RAY DIFFRACTION 3.80Å
e4cwuN2[N:134-296,N:375-433] Image Pymol Jmol Links: PDB, SCOP, CATH
e4v4uA1[A:134-296,A:375-433] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
PENTON PROTEIN ; ELECTRON MICROSCOPY
e4v4uB1[B:134-296,B:375-433] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
PENTON PROTEIN ; ELECTRON MICROSCOPY
e4v4uC1[C:134-296,C:375-433] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
PENTON PROTEIN ; ELECTRON MICROSCOPY
e4v4uD1[D:134-296,D:375-433] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
PENTON PROTEIN ; ELECTRON MICROSCOPY
e4v4uE1[E:134-296,E:375-433] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
PENTON PROTEIN ; ELECTRON MICROSCOPY
e6b1tM1[M:134-296,M:377-433] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6cgvN1[N:134-296,N:375-433] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; X-RAY DIFFRACTION 3.8Å
e4aqqA2[A:134-413] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
L2 PROTEIN III (PENTON BASE) ; X-RAY DIFFRACTION 4.75Å
e5tx1N2[N:121-299,N:324-388] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton ; ELECTRON MICROSCOPY
e6hcrz2[z:134-313,z:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcrA1[A:134-313,A:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcrB2[B:134-313,B:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcrC1[C:134-313,C:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcrD2[D:134-313,D:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcrE2[E:134-313,E:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcrF2[F:134-313,F:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcrG2[G:134-313,G:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcrH1[H:134-313,H:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcrI2[I:134-313,I:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcrJ2[J:134-313,J:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcrK1[K:134-313,K:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcrL1[L:134-313,L:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcrM1[M:134-313,M:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcrN1[N:134-313,N:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcrO1[O:134-313,O:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcrP2[P:134-313,P:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcrQ1[Q:134-313,Q:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcrR1[R:134-313,R:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcrS2[S:134-313,S:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcrT2[T:134-313,T:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcrV2[V:134-313,V:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcrW2[W:134-313,W:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcrX2[X:134-313,X:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcrY1[Y:134-313,Y:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcrZ1[Z:134-313,Z:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcra2[a:134-313,a:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcrb1[b:134-313,b:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcrc1[c:134-313,c:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcrd2[d:134-313,d:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcre1[e:134-313,e:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcrf1[f:134-313,f:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcrg1[g:134-313,g:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcrh2[h:134-313,h:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcri1[i:134-313,i:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcrj2[j:134-313,j:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcrk2[k:134-313,k:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcrl1[l:134-313,l:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcrm2[m:134-313,m:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcrn2[n:134-313,n:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcro2[o:134-313,o:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcrp1[p:134-313,p:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcrq2[q:134-313,q:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcrr2[r:134-313,r:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcrs1[s:134-313,s:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcrt2[t:134-313,t:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcru2[u:134-313,u:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcrv1[v:134-313,v:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcrw1[w:134-313,w:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcrx1[x:134-313,x:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcry2[y:134-313,y:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcr11[1:134-313,1:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcr21[2:134-313,2:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcr32[3:134-313,3:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcr42[4:134-313,4:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcr51[5:134-313,5:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcr62[6:134-313,6:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcr71[7:134-313,7:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcr82[8:134-313,8:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6hcr91[9:134-313,9:367-428] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6qi5M2[M:99-311] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6z7qA1[A:132-295,A:315-370] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6z7qB2[B:132-295,B:315-370] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6z7qC1[C:132-295,C:315-370] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6z7qD2[D:132-295,D:315-370] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6z7qE1[E:132-295,E:315-370] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6z7nM2[M:132-377] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e6ybaM2[M:132-292,M:315-370] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e7rd1M1[M:130-302,M:339-394] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e7s78N2[N:134-302,N:374-433] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
e7tauN1[N:121-299,N:325-388] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Penton protein ; ELECTRON MICROSCOPY
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