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
Representatives:
e1i12A1[A:3-159] nonrep Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
GLUCOSAMINE-PHOSPHATE N-ACETYLTRANSFERASE ; ligands: ACO,IMD ; X-RAY DIFFRACTION 1.30Å
e4m3sA1[A:1-160] nonrep Image Pymol Jmol Links: PDB, SCOP, CATH
Uncharacterized protein ; ligands: CL,EPE,SO4 ; X-RAY DIFFRACTION 1.30Å
e5hgzA1[A:1-211] nonrep Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
N-alpha-acetyltransferase 60 ; ligands: ACO,MLA ; X-RAY DIFFRACTION 1.383Å
e1gheA1[A:4-173] nonrep Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
ACETYLTRANSFERASE ; ligands: ACO ; X-RAY DIFFRACTION 1.40Å
e2aj6A1[A:1-118] nonrep Image Pymol Jmol Links: PDB, SCOP, CATH
hypothetical protein MW0638 ; ligands: SO4,UNL ; X-RAY DIFFRACTION 1.50Å
Domain assembly:
Domain assembly:
e2fl4A1[A:1-146] nonrep Image Pymol Jmol Links: PDB, SCOP, CATH
spermine/spermidine acetyltransferase ; X-RAY DIFFRACTION 1.6Å
e2jdcA1[A:2-146] nonrep Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
GLYPHOSATE N-ACETYLTRANSFERASE ; ligands: CAO,SO4 ; X-RAY DIFFRACTION 1.6Å
e5ib0A1[A:1-137] nonrep Image Pymol Jmol Links: PDB, SCOP, CATH
Uncharacterized protein PA4534 ; ligands: ACO,GOL ; X-RAY DIFFRACTION 1.65Å
e1mk4A1[A:0-156] nonrep Image Pymol Jmol Links: PDB, SCOP, CATH
Hypothetical protein yqjY ; X-RAY DIFFRACTION 1.7Å
e1vhsA1[A:0-164] nonrep Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
similar to phosphinothricin acetyltransferase ; X-RAY DIFFRACTION 1.70Å
e1y7rA1[A:1-133] nonrep Image Pymol Jmol Links: PDB, SCOP, CATH
hypothetical protein SA2161 ; ligands: PO4 ; X-RAY DIFFRACTION 1.70Å
e1z4rA1[A:497-658] nonrep Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
GENERAL CONTROL OF AMINO ACID SYNTHESIS PROTEIN 5-LIKE 2 ; ligands: ACO ; X-RAY DIFFRACTION 1.74Å
e1wwzA1[A:1-157] nonrep Image Pymol Jmol Links: PDB, SCOP, CATH
hypothetical protein PH1933 ; ligands: ACO ; X-RAY DIFFRACTION 1.75Å
e1cjwA1[A:30-195] nonrep Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
PROTEIN (SEROTONIN N-ACETYLTRANSFERASE) ; ligands: COT ; X-RAY DIFFRACTION 1.8Å
e1n71A1[A:1-180] nonrep Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
aac(6')-Ii ; ligands: COA ; X-RAY DIFFRACTION 1.80Å
e1vkcA1[A:2-150] nonrep Image Pymol Jmol Links: PDB, SCOP, CATH
putative acetyl transferase ; ligands: IOD ; X-RAY DIFFRACTION 1.89Å
e1y9wA1[A:1-140] nonrep Image Pymol Jmol Links: PDB, SCOP, CATH
Acetyltransferase ; X-RAY DIFFRACTION 1.9Å
e1yvoA1[A:4-172] nonrep Image Pymol Jmol Links: PDB, SCOP, CATH
CONSERVED HYPOTHETICAL PROTEIN ; X-RAY DIFFRACTION 1.9Å
e2g3aA1[A:1-137] nonrep Image Pymol Jmol Links: PDB, SCOP, CATH
acetyltransferase ; X-RAY DIFFRACTION 1.9Å
e1tiqA1[A:2-174] nonrep Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Protease synthase and sporulation negative regulatory protein PAI 1 ; ligands: COA,DTT ; X-RAY DIFFRACTION 1.90Å
e1z4eA1[A:4-153] nonrep Image Pymol Jmol Links: PDB, SCOP, CATH
transcriptional regulator ; X-RAY DIFFRACTION 2.0Å
e2cy2A1[A:1-174] nonrep Image Pymol Jmol Links: PDB, SCOP, CATH
PROBABLE ACETYLTRANSFERASE ; ligands: ACO ; X-RAY DIFFRACTION 2.0Å
e2fe7A1[A:3-158] nonrep Image Pymol Jmol Links: PDB, SCOP, CATH
probable N-acetyltransferase ; X-RAY DIFFRACTION 2.0Å
Domain assembly:
Domain assembly:
e1s3zA1[A:-1-145] nonrep Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
aminoglycoside 6'-N-acetyltransferase ; ligands: COA,NI,RIO,SO4 ; X-RAY DIFFRACTION 2.000Å
e2ganA1[A:1-182] nonrep Image Pymol Jmol Links: PDB, SCOP, CATH
182aa long hypothetical protein ; ligands: EDO,SO4 ; X-RAY DIFFRACTION 2.1Å
e2ae6A1[A:1-161] nonrep Image Pymol Jmol Links: PDB, SCOP, CATH
ACETYLTRANSFERASE, GNAT FAMILY ; ligands: GOL,MG ; X-RAY DIFFRACTION 2.19Å
e1ufhA1[A:2-156] nonrep Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
YYCN protein ; X-RAY DIFFRACTION 2.2Å
e2ge3A1[A:6-169] nonrep Image Pymol Jmol Links: PDB, SCOP, CATH
PROBABLE ACETYLTRANSFERASE ; ligands: ACO ; X-RAY DIFFRACTION 2.25Å
e4hnyD1[D:2-239] nonrep Image Pymol Jmol Links: PDB, SCOP, CATH
N-TERMINAL ACETYLTRANSFERASE A COMPLEX CATALYTIC SUBUNIT ARD1 ; X-RAY DIFFRACTION 2.25Å
e1bo4A1[A:25-161] nonrep Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
PROTEIN (SERRATIA MARCESCENS AMINOGLYCOSIDE-3-N-ACETYLTRANSFERASE) ; ligands: COA,SPD ; X-RAY DIFFRACTION 2.3Å
e4hnxB1[B:2-54,B:79-238] nonrep Image Pymol Jmol Links: PDB, SCOP, CATH
N-terminal acetyltransferase A complex catalytic subunit ARD1 ; ligands: G4P ; X-RAY DIFFRACTION 2.339Å
e1y9kA1[A:1-152] nonrep Image Pymol Jmol Links: PDB, SCOP, CATH
IAA ACETYLTRANSFERASE ; X-RAY DIFFRACTION 2.39Å
e5l7jA2[A:309-459] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
ELP3 family ; ligands: ZN ; X-RAY DIFFRACTION 2.15Å
e5l7lA2[A:310-446] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
ELP3 family, ELP3 family ; ligands: ZN ; X-RAY DIFFRACTION 2.59Å
e2r7hA1[A:18-176] Image Pymol Jmol Links: PDB, SCOP, CATH
Putative D-alanine N-acetyltransferase of GNAT family ; ligands: ETX ; X-RAY DIFFRACTION 1.85Å
e2r7hB1[B:18-176] Image Pymol Jmol Links: PDB, SCOP, CATH
Putative D-alanine N-acetyltransferase of GNAT family ; ligands: ETX ; X-RAY DIFFRACTION 1.85Å
e1b87A1[A:1-180] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
PROTEIN (AMINOGLYCOSIDE N6'-ACETYLTRANSFERASE TYPE 1) ; ligands: ACO ; X-RAY DIFFRACTION 2.7Å
e2bswA1[A:2-146] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
GLYPHOSATE N-ACETYLTRANSFERASE ; ligands: CAO,GOL,SO4 ; X-RAY DIFFRACTION 1.630Å
e1yvkA1[A:5-156] Image Pymol Jmol Links: PDB, SCOP, CATH
hypothetical protein BSU33890 ; ligands: COA ; X-RAY DIFFRACTION 3.0Å
e1n71D1[D:1-180] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
aac(6')-Ii ; ligands: COA,SO4 ; X-RAY DIFFRACTION 1.80Å
e2a4nA1[A:1-180] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
aac(6')-Ii ; ligands: COA,SO4 ; X-RAY DIFFRACTION 2.20Å
e1n71B1[B:1-179] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
aac(6')-Ii ; ligands: COA ; X-RAY DIFFRACTION 1.80Å
e1n71C1[C:1-179] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
aac(6')-Ii ; ligands: COA,SO4 ; X-RAY DIFFRACTION 1.80Å
e2a4nB1[B:1-179] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
aac(6')-Ii ; ligands: COA,SO4 ; X-RAY DIFFRACTION 2.20Å
e1y9kB1[B:1-152] Image Pymol Jmol Links: PDB, SCOP, CATH
IAA ACETYLTRANSFERASE ; X-RAY DIFFRACTION 2.39Å
e1y9kD1[D:1-151] Image Pymol Jmol Links: PDB, SCOP, CATH
IAA ACETYLTRANSFERASE ; X-RAY DIFFRACTION 2.39Å
e1y9kC1[C:2-151] Image Pymol Jmol Links: PDB, SCOP, CATH
IAA ACETYLTRANSFERASE ; X-RAY DIFFRACTION 2.39Å
e1yvkB1[B:5-156] Image Pymol Jmol Links: PDB, SCOP, CATH
hypothetical protein BSU33890 ; ligands: COA ; X-RAY DIFFRACTION 3.0Å
e1yvkC1[C:5-156] Image Pymol Jmol Links: PDB, SCOP, CATH
hypothetical protein BSU33890 ; ligands: COA ; X-RAY DIFFRACTION 3.0Å
e1yvkD1[D:5-156] Image Pymol Jmol Links: PDB, SCOP, CATH
hypothetical protein BSU33890 ; ligands: COA ; X-RAY DIFFRACTION 3.0Å
e2jddA1[A:2-146] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
GLYPHOSATE N-ACETYLTRANSFERASE ; ligands: 3PG,ACO,SO4 ; X-RAY DIFFRACTION 1.600Å
e3w6sA1[A:5-229] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
MPR1 PROTEIN ; ligands: MG,P6G ; X-RAY DIFFRACTION 1.9Å
e3w6sB1[B:5-228] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
MPR1 PROTEIN ; ligands: P6G ; X-RAY DIFFRACTION 1.9Å
e3w6sC1[C:5-228] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
MPR1 PROTEIN ; ligands: P6G ; X-RAY DIFFRACTION 1.9Å
e3w91A1[A:4-229] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
MPR1 PROTEIN ; X-RAY DIFFRACTION 2.1Å
e3w91B1[B:5-228] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
MPR1 PROTEIN ; X-RAY DIFFRACTION 2.1Å
e3w91C1[C:1-228] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
MPR1 PROTEIN ; X-RAY DIFFRACTION 2.1Å
e3w6xA1[A:5-229] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
MPR1 PROTEIN ; ligands: HZP,P6G ; X-RAY DIFFRACTION 2.3Å
e3w6xB1[B:5-229] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
MPR1 PROTEIN ; ligands: HZP,P6G ; X-RAY DIFFRACTION 2.3Å
e3w6xC1[C:5-229] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
MPR1 PROTEIN ; ligands: CL,HZP,P6G ; X-RAY DIFFRACTION 2.3Å
e3w6xE1[E:5-229] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
MPR1 PROTEIN ; ligands: CL,P6G ; X-RAY DIFFRACTION 2.3Å
e3w6xG1[G:5-229] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
MPR1 PROTEIN ; ligands: CL,P6G ; X-RAY DIFFRACTION 2.3Å
e3w6xH1[H:5-229] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
MPR1 PROTEIN ; ligands: CL,P6G ; X-RAY DIFFRACTION 2.3Å
e3w6xI1[I:5-229] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
MPR1 PROTEIN ; ligands: P6G ; X-RAY DIFFRACTION 2.3Å
e3w6xJ1[J:5-229] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
MPR1 PROTEIN ; ligands: P6G ; X-RAY DIFFRACTION 2.3Å
e3w6xL1[L:5-229] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
MPR1 PROTEIN ; ligands: P6G ; X-RAY DIFFRACTION 2.3Å
e3w6xD1[D:5-228] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
MPR1 PROTEIN ; ligands: CL,P6G ; X-RAY DIFFRACTION 2.3Å
e3w6xF1[F:5-228] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
MPR1 PROTEIN ; ligands: CL,HZP,P6G ; X-RAY DIFFRACTION 2.3Å
e3w6xK1[K:5-228] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
MPR1 PROTEIN ; ligands: P6G ; X-RAY DIFFRACTION 2.3Å
e2wpwB2[B:6-157] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
ORF14 ; ligands: ACO ; X-RAY DIFFRACTION 2.38Å
e2reeA2[A:226-358,A:382-424] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
CurA ; ligands: CL,GOL,SO4 ; X-RAY DIFFRACTION 1.950Å
e2wpxA3[A:5-156] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
ORF14 ; ligands: ACO,GOL ; X-RAY DIFFRACTION 2.31Å
e2wpxB3[B:5-156] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
ORF14 ; ligands: ACO,GOL ; X-RAY DIFFRACTION 2.31Å
e2wpwC3[C:7-157] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
ORF14 ; ligands: ACO ; X-RAY DIFFRACTION 2.38Å
e2wpwD3[D:7-157] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
ORF14 ; ligands: ACO ; X-RAY DIFFRACTION 2.38Å
e2reeB2[B:226-358,B:382-424] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
CurA ; ligands: GOL,SO4 ; X-RAY DIFFRACTION 1.950Å
e2refA2[A:222-357,A:382-424] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
CurA ; ligands: ACO ; X-RAY DIFFRACTION 2.750Å
e2refB2[B:222-357,B:382-424] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
CurA ; ligands: ACO ; X-RAY DIFFRACTION 2.750Å
e2wpwA2[A:4-157] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
ORF14 ; ligands: ACO ; X-RAY DIFFRACTION 2.38Å
e1cm0A1[A:492-653] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
P300/CBP ASSOCIATING FACTOR ; ligands: COA ; X-RAY DIFFRACTION 2.3Å
e5gcnA1[A:3-161] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
HISTONE ACETYLTRANSFERASE GCN5 ; ligands: COA ; SOLUTION NMR
e1yghA1[A:99-257] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
PROTEIN (TRANSCRIPTIONAL ACTIVATOR GCN5) ; ligands: GOL ; X-RAY DIFFRACTION 1.90Å
e1m1dA1[A:48-205] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
TGCN5 HISTONE ACETYL TRANSFERASE ; X-RAY DIFFRACTION 2.2Å
e1pu9A1[A:48-205] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
HAT A1 ; ligands: COA ; X-RAY DIFFRACTION 2.3Å
e1m1dC1[C:349-505] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
TGCN5 HISTONE ACETYL TRANSFERASE ; X-RAY DIFFRACTION 2.2Å
e1puaA1[A:49-205] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
HAT A1 ; ligands: COA ; X-RAY DIFFRACTION 2.3Å
e1q2cA1[A:49-205] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
histone acetyltransferase GCN5 ; ligands: COA ; X-RAY DIFFRACTION 2.00Å
e1q2dA1[A:49-205] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
HISTONE ACETYLTRANSFERASE GCN5 ; ligands: COA ; X-RAY DIFFRACTION 2.25Å
e1qsnA1[A:49-205] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
TGCN5 HISTONE ACETYL TRANSFERASE ; ligands: COA ; X-RAY DIFFRACTION 2.000Å
e1qsrA1[A:49-205] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
TGCN5 HISTONE ACETYL TRANSFERASE ; ligands: ACO ; X-RAY DIFFRACTION 2.0Å
e1qstA1[A:49-205] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
TGCN5 HISTONE ACETYL TRANSFERASE ; ligands: EPE ; X-RAY DIFFRACTION 1.7Å
e1cm0B1[B:492-653] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
P300/CBP ASSOCIATING FACTOR ; ligands: COA ; X-RAY DIFFRACTION 2.3Å
e1yghB1[B:99-257] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
PROTEIN (TRANSCRIPTIONAL ACTIVATOR GCN5) ; ligands: GOL ; X-RAY DIFFRACTION 1.90Å
e4nsqA1[A:492-652] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Histone acetyltransferase KAT2B ; ligands: COA ; X-RAY DIFFRACTION 2.31Å
e4nsqB1[B:492-652] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Histone acetyltransferase KAT2B ; ligands: COA ; X-RAY DIFFRACTION 2.31Å
e4nsqC1[C:492-652] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Histone acetyltransferase KAT2B ; ligands: COA ; X-RAY DIFFRACTION 2.31Å
e4nsqD1[D:492-652] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Histone acetyltransferase KAT2B ; ligands: COA ; X-RAY DIFFRACTION 2.31Å
e5e96A1[A:1-116,A:141-179] Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
Aminoglycoside 6'-acetyltransferase ; ligands: EDO,PO4 ; X-RAY DIFFRACTION 2.100Å
e1u6mA1[A:2-190] nonrep Image Pymol Jmol Links: PDB, SCOP, CATH
acetyltransferase, GNAT family ; ligands: SO4 ; X-RAY DIFFRACTION 2.4Å
e1qsmA1[A:7-156] nonrep Image Pymol Jmol Links: PDB, SCOP, CATH, PubMed, DOI
HPA2 HISTONE ACETYLTRANSFERASE ; ligands: ACO ; X-RAY DIFFRACTION 2.400Å
e2fiaA1[A:1-157] nonrep Image Pymol Jmol Links: PDB, SCOP, CATH
acetyltransferase ; X-RAY DIFFRACTION 2.6Å
e2euiA1[A:1-153] nonrep Image Pymol Jmol Links: PDB, SCOP, CATH
Probable acetyltransferase ; X-RAY DIFFRACTION 2.8Å
Pseudo group of domains that do not map to PFam family profiles. Domains inside should not be considered as in one family.
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